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Introduction: Cold stress is the primary factor that limits the growth and development of Kobresia pygmaea in the Tibetan Plateau, China. Chitosan (CTS) has been recognized for its ability to enhance agricultural production and tolerance to stress. Methods: This study examined the effect of treating seedlings under cold stress with chitosan. Results and Discussion: The results demonstrated that cold stress inhibited the growth of seedlings and adversely affected the photosynthetic capacity [net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum efficiency of photosystem II (Fv/Fm), quantum yield of photosystem II (φ PSII), electron transport rate (ETR), and non-light-induced non-photochemical fluorescence quenching Y(NPQ)] and destroyed PSII and the chloroplast structure. Under regular temperatures, low concentrations of CTS (0.005% and 0.01%) inhibited the soluble protein content, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activity, and photosynthetic capacity. However, the application of 0.015% CTS increased the levels of soluble sugar, fructose, and protein, as well as those of the levels of ions, such as iron and magnesium, chlorophyll, photosynthetic capacity, and the activities of Rubisco, superoxide dismutase, and phenylalanine amino-lyase (PAL). Under cold stress, treatment with CTS decreased the contents of starch and sucrose; improved the contents of fructose, soluble protein, and antioxidants, such as ascorbic acid and glutathione; and enhanced the photosynthesis capacity and the activities of Rubisco, chitinase, and PAL. Exogenous CTS accelerated the development of the vascular bundle, mitigated the damage to chloroplast structure induced by cold, and promoted the formation of well-organized thylakoids and grana lamellae. Additionally, CTS upregulated the expression of genes related to cold tolerance in K. pygmaea , such as KpBSK2 / KpERF / KpDRE326. These findings indicate that CTS enhances the cold tolerance in K. pygmaea by improving development of the vascular bundle, increasing the accumulation of solutes and antioxidants, regulating the transformation of carbohydrates, repairing the chloroplast structure, and maintaining the photosynthetic capacity and Rubisco activity. [ABSTRACT FROM AUTHOR]

We honor Professor Hartmut Karl Lichtenthaler, a versatile pioneer of photosynthesis research, plant physiology, isoprenoid biochemistry, and stress physiology of plants, for his groundbreaking and creative contributions to plant science. His innovative research on the chemical composition, ultrastructure, and function of chloroplasts and his detection of the major methylerythritol 4-phosphate (MEP) isoprenoid biosynthetic pathway in plants is key to our current understanding of the physiology and biochemistry of photosynthesis systems. His ingenious use of the powerful laser-induced chlorophyll a fluorescence imaging has helped us better understand the stress response processes in plant leaves. In this tribute, we present a summary of Lichtenthalerꞌs career, significant scientific contributions, editorial engagement, promotion of international cooperation, many honors, and awards, as well as his devotion to hiking and mountaineering.

Background and Aims: Avicennia marina, a pioneer recretohalophyte mangrove species living in intertidal wetlands, has high salinity tolerance. To understand the mechanism of salt adaptability, the seedlings of A. marina were treated with different salinities. We hypothesized that A. marina would demonstrate adaptive mechanisms at both physiological and molecular levels to tolerate tidal salinity through ion selectivity and chloride homeostasis. Methods: In this study, the combination of growth, chlorophyll fluorescence analysis, electron microscopy, electrophysiological and molecular approaches were employed to investigate the mechanism of salt adaptability of A. marina seedlings. Results: 400 mM NaCl promoted chloroplast development, and chlorophyll fluorescence Fv/Fm, Fv/Fo, and qP decreased with increasing NaCl concentration, while ETR remained stable. NaCl contributed to increased Na+ and Cl− content in roots, leaves and exudates of salt glands, while relative high Cl− was stored in the roots and more Na+ in the leaves. Flux measurements of Na+, Cl−, K+, H+, and NO3− in the leaf salt glands and the root tips treated with 0 and 400 mM NaCl indicated the presence of an ion selectivity that was suppressed by specific Na+/H+ antiporter inhibitor amiloride, PM H+-ATPase inhibitor vanadate, and Na+:K+:2Cl− cotransporter inhibitor bumetanide. Further analysis showed that the expressions of chloride transport-related homolog genes CLCc, CLCf, and CCC1 were significantly up-regulated, whereas CLCd was down-regulated under salt treatment. Conclusions: In conclusion, the chloride homeostasis regulated by salt ion secretion selectivity and transport-associated genes in leaf and root serves a crucial role in the salt tolerance of A. marina. [ABSTRACT FROM AUTHOR]

IntroductionCold stress is the primary factor that limits the growth and development of Kobresia pygmaea in the Tibetan Plateau, China. Chitosan (CTS) has been recognized for its ability to enhance agricultural production and tolerance to stress.MethodsThis study examined the effect of treating seedlings under cold stress with chitosan.Results and DiscussionThe results demonstrated that cold stress inhibited the growth of seedlings and adversely affected the photosynthetic capacity [net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), maximum efficiency of photosystem II (Fv/Fm), quantum yield of photosystem II (φPSII), electron transport rate (ETR), and non-light-induced non-photochemical fluorescence quenching Y(NPQ)] and destroyed PSII and the chloroplast structure. Under regular temperatures, low concentrations of CTS (0.005% and 0.01%) inhibited the soluble protein content, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activity, and photosynthetic capacity. However, the application of 0.015% CTS increased the levels of soluble sugar, fructose, and protein, as well as those of the levels of ions, such as iron and magnesium, chlorophyll, photosynthetic capacity, and the activities of Rubisco, superoxide dismutase, and phenylalanine amino-lyase (PAL). Under cold stress, treatment with CTS decreased the contents of starch and sucrose; improved the contents of fructose, soluble protein, and antioxidants, such as ascorbic acid and glutathione; and enhanced the photosynthesis capacity and the activities of Rubisco, chitinase, and PAL. Exogenous CTS accelerated the development of the vascular bundle, mitigated the damage to chloroplast structure induced by cold, and promoted the formation of well-organized thylakoids and grana lamellae. Additionally, CTS upregulated the expression of genes related to cold tolerance in K. pygmaea, such as KpBSK2/KpERF/KpDRE326. These findings indicate that CTS enhances the cold tolerance in K. pygmaea by improving development of the vascular bundle, increasing the accumulation of solutes and antioxidants, regulating the transformation of carbohydrates, repairing the chloroplast structure, and maintaining the photosynthetic capacity and Rubisco activity.

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Water deficit is the major stress factor magnified by climate change that causes the most reductions in plant productivity. Knowledge of photosystem II (PSII) response mechanisms underlying crop vulnerability to drought is critical to better understanding the consequences of climate change on crop plants. Salicylic acid (SA) application under drought stress may stimulate PSII function, although the exact mechanism remains essentially unclear. To reveal the PSII response mechanism of celery plants sprayed with water (WA) or SA, we employed chlorophyll fluorescence imaging analysis at 48 h, 96 h, and 192 h after watering. The results showed that up to 96 h after watering, the stroma lamellae of SA-sprayed leaves appeared dilated, and the efficiency of PSII declined, compared to WA-sprayed plants, which displayed a better PSII function. However, 192 h after watering, the stroma lamellae of SA-sprayed leaves was restored, while SA boosted chlorophyll synthesis, and by ameliorating the osmotic potential of celery plants, it resulted in higher relative leaf water content compared to WA-sprayed plants. SA, by acting as an antioxidant under drought stress, suppressed phototoxicity, thereby offering PSII photoprotection, together with enhanced effective quantum yield of PSII photochemistry (ΦPSII) and decreased quantity of singlet oxygen (1O2) generation compared to WA-sprayed plants. The PSII photoprotection mechanism induced by SA under drought stress was triggered by non-photochemical quenching (NPQ), which is a strategy to protect the chloroplast from photo-oxidative damage by dissipating the excess light energy as heat. This photoprotective mechanism, triggered by NPQ under drought stress, was adequate in keeping, especially in high-light conditions, an equal fraction of open PSII reaction centers (qp) as of non-stress conditions. Thus, under water deficit stress, SA activates a regulatory network of stress and light energy partitioning signaling that can mitigate, to an extent, the water deficit stress on PSII functioning. [ABSTRACT FROM AUTHOR]

This study focuses on optimizing chlorophyll extraction techniques, in which leaf discs are cut from places on the leaf blade to enhance chlorophyll concentration in sesame (Sesamum indicum L.) leaves. Thirty sesame genotypes, categorized into light green (LG), middle green (MG), and deep green (DG) pigment groups based on leaf coloration, were selected from a larger pool of field-grown accessions. The investigation involved determining optimal Soil Plant Analysis Development (SPAD) value index measurements, quantifying pigment concentrations, exploring extraction solvents, and selecting suitable leaf disk positions. Significant variations in chlorophyll content were observed across genotypes, greenness categories, and leaf disk positions. The categorization of genotypes into DG, MG, and LG groups revealed a correlation between leaf appearance and chlorophyll content. The study highlighted a consistent relationship between carotenoids and chlorophyll, indicating their role in adaptation to warm environments. An examination of leaf disk positions revealed a significant chlorophyll gradient along the leaf blade, emphasizing the need for standardized protocols. Chlorophyll extraction experiments identified DMSO and 96% ethanol, particularly in those incubated for 10 min at 85 °C, as effective choices. This recommendation considers factors like cost-effectiveness, time efficiency, safety, and environmental regulations, ensuring consistent and simplified extraction processes. For higher chlorophyll extraction, focusing on leaf tips and the 75% localization along the sesame leaf blade is suggested, as this consistently yields increased chlorophyll content. Furthermore, our examination revealed significant anatomical variations in the internal structure of the mesophyll tissue leaves between deep green and light green sesame plants, primarily linked to chloroplast density and pigment-producing structures. Our findings, therefore, provide insightful knowledge of chlorophyll gradients and encourage the use of standardized protocols that enable researchers to refine their experimental designs for precise and comparable chlorophyll measurements. The recommended solvent choices ensure reliable outcomes in plant physiology, ecology, and environmental studies. [ABSTRACT FROM AUTHOR]

Photosystem II (PSII) functions were investigated in basil (Ocimum basilicum L.) plants sprayed with 1 mM salicylic acid (SA) under non-stress (NS) or mild drought-stress (MiDS) conditions. Under MiDS, SA-sprayed leaves retained significantly higher (+36%) chlorophyll content compared to NS, SA-sprayed leaves. PSII efficiency in SA-sprayed leaves under NS conditions, evaluated at both low light (LL, 200 μmol photons m−2 s−1) and high light (HL, 900 μmol photons m−2 s−1), increased significantly with a parallel significant decrease in the excitation pressure at PSII (1-qL) and the excess excitation energy (EXC). This enhancement of PSII efficiency under NS conditions was induced by the mechanism of non-photochemical quenching (NPQ) that reduced singlet oxygen (1O2) production, as indicated by the reduced quantum yield of non-regulated energy loss in PSII (ΦNO). Under MiDS, the thylakoid structure of water-sprayed leaves appeared slightly dilated, and the efficiency of PSII declined, compared to NS conditions. In contrast, the thylakoid structure of SA-sprayed leaves did not change under MiDS, while PSII functionality was retained, similar to NS plants at HL. This was due to the photoprotective heat dissipation by NPQ, which was sufficient to retain the same percentage of open PSII reaction centers (qp), as in NS conditions and HL. We suggest that the redox status of the plastoquinone pool (qp) under MiDS and HL initiated the acclimation response to MiDS in SA-sprayed leaves, which retained the same electron transport rate (ETR) with control plants. Foliar spray of SA could be considered as a method to improve PSII efficiency in basil plants under NS conditions, at both LL and HL, while under MiDS and HL conditions, basil plants could retain PSII efficiency similar to control plants. [ABSTRACT FROM AUTHOR]

Oligosaccharides, as a wide type of polysaccharide, have a broad antimicrobial spectrum and promote development as plant growth stimulants. To investigate the regulation effects of different oligosaccharides on the dynamic changes of chlorophyll content, leaf fluorescence, root activity and morphology, and chloroplast ultrastructure, as well as the yields and yield components of strawberry and cucumber, typical greenhouse experiments were conducted over two years (2021–2022). The experimental plants were foliar sprayed with tap water (CK), chitosan oligosaccharide (CSOS), and mixed oligosaccharides (MixOS) five times before flowering. The conventional management (CM) was conducted as a conventional control. The findings of the present study suggest that the application of MixOS has the greatest regulation effects on delayed leaf senescence, well-developed roots, and higher fruit productions of strawberry and cucumber. Exogenous MixOS resulted in significant increases in SPAD values, maximum photochemical efficiency (Fv/Fm), and photochemical quenching coefficiency (qP); they were increased by 1.94–28.96%, 5.41–33.89%, and 9.93–62.07%, compared to the CSOS, CM, and CK treatments, respectively. The orderly and steady structure of thylakoids in the chloroplast, and the randomly distributed starch grains, could be clearly observed in the MixOS treatment, while the non-photochemical quenching (NPQ) was correspondingly reduced by 19.04–45.92%. Meanwhile, the remarkable promotion of root activity and root surface morphology indicators (i.e., root length, surface area, average diameter, and volume) could be observed when exposed to the MixOS treatments, and the total yields of strawberry and cucumber were all increased by 12.40–25.57%. These findings suggest that the mixed oligosaccharides mainly promote the coordinated growth of root and shoot, which leads to the improved yields of strawberry and cucumber. [ABSTRACT FROM AUTHOR]

Understanding the light adaptation of plants is critical for conservation. Platycrater arguta, an endangered deciduous shrub endemic to East Asia, possesses high ornamental and phylogeographic value. However, the weak environmental adaptability of P. arguta species has limited its general growth and conservation. To obtain a deeper understanding of the P. arguta growth conditions, we examined the leaf morphology and physiology via anatomical and chloroplast ultrastructural analyses following exposure to different natural light intensities (full light, 40%, and 10%). The findings indicated that P. arguta seedings in the 10% light intensity had significantly improved leaf morphological characteristics and specific leaf area compared to those exposed to other intensities. The net photosynthetic rate, chlorophyll (Chl) content, photosynthetic nitrogen use efficiency (PNUE), and photosynthetic phosphorus use efficiency (PPUE) exhibited marked increases at a 10% light intensity compared to both 40% light and full light intensities, whereas the light compensation point and dark respiration levels reached their lowest values under the 10% light condition. With reduced light, leaf thickness, palisade tissue, spongy tissue, and stomatal density significantly decreased, whereas the stomatal length, stomatal width, and stomatal aperture were significantly elevated. When exposed to 10% light intensity, the ultrastructure of chloroplasts was well developed, chloroplasts and starch grain size, the number of grana, and thylakoids all increased significantly, while the number of plastoglobules was significantly reduced. Relative distance phenotypic plasticity index analysis exhibited that P. arguta adapts to varying light environments predominantly by adjusting PPUE, Chl b, PNUE, chloroplast area, and the activity of PSII reaction centers. We proposed that P. arguta efficiently utilizes low light to reconfigure its energy metabolism by regulating its leaf structure, photosynthetic capacity, nutrient use efficiency, and chloroplast development. [ABSTRACT FROM AUTHOR]

Colored-leaf poplar is increasingly popular due to its great ornamental values and application prospects. However, the photosynthetic characteristics of these colored-leaf cultivars have not been well understood. In this study, the photosynthetic differences between green-leaf poplar Populus deltoids Linn. "2025" (L2025) and colored-leaf cultivars 'Zhonghong poplar' (ZHP), 'Quanhong poplar' (QHP), and 'Caihong poplar' (CHP) were investigated on several levels, including chloroplast ultrastructure observation, photosynthetic physiological characteristics, and expression analysis of key genes. The results showed that the photosynthetic performance of ZHP was basically consistent with that of L2025, while the ranges of light energy absorption and efficiency of light energy utilization decreased to different degrees in CHP and QHP. A relatively low water use efficiency and high dark respiration rate were observed in QHP, suggesting a relatively weak environmental adaptability. The differences in chloroplast structure in different colored-leaf poplars were further observed by transmission electron microscopy. The disorganization of thylakoid in CHP was considered an important reason, resulting in a significant decrease in chlorophyll content compared with other poplar cultivars. Interestingly, CHP exhibited extremely high photosynthetic electron transport activity and photochemical efficiency, which were conductive to maintaining its relatively high photosynthetic performance. The actual quantum yield of PSII photochemistry of ZHP was basically the same as that of QHP, while the relatively high photosynthetic performance indexes in ZHP suggested a more optimized photosynthetic apparatus, which was crucial for the improvement of photosynthetic efficiency. The differential expressions of a series of key genes in different colored-leaf poplars provided a reasonable explanation for anthocyanin accumulation and specific photosynthetic processes. [ABSTRACT FROM AUTHOR]

The present study aims to gain insights into the response mechanisms of drought stress tolerance among two contrasting melon (Cucumis melo L.) genotypes. Drought stress was imposed by polyethylene glycol (10%) for 7 days and various physiochemical and molecular characteristics were analyzed on different days of drought stress treatment. Results revealed that the drought-sensitive genotype (MG-II) was significantly affected by drought stress, as evidenced from the elevation in hydrogen peroxide (H2O2), malondialdehyde content (MDA), and electrolyte leakage (EC). Furthermore, drought stress significantly hindered the vegetative growth, chlorophyll fluorescence, photosynthetic pigments, and leaf gas exchange characteristics of MG-II genotypes. In contrast, the drought-resistant genotype (MG-I) exhibited a robust response to drought stress, characterized by marked upregulation in the antioxidant enzyme genes and activities, which in turn resulted in a decrease in oxidative damage and improved vegetative growth and photosynthetic functions. Additionally, transmission electron microscopy (TEM) revealed that the oxidative damage triggered by drought stress was more severe in the MG-II genotype, which exhibited an irregular chloroplast shape compared to the MG-I. These findings may potentially enhance our comprehension of coping strategies involved in drought stress tolerance and provide materials for future melon breeding and molecular studies. [ABSTRACT FROM AUTHOR]

Oligosaccharides, as a wide type of polysaccharide, have a broad antimicrobial spectrum and promote development as plant growth stimulants. To investigate the regulation effects of different oligosaccharides on the dynamic changes of chlorophyll content, leaf fluorescence, root activity and morphology, and chloroplast ultrastructure, as well as the yields and yield components of strawberry and cucumber, typical greenhouse experiments were conducted over two years (2021–2022). The experimental plants were foliar sprayed with tap water (CK), chitosan oligosaccharide (CSOS), and mixed oligosaccharides (MixOS) five times before flowering. The conventional management (CM) was conducted as a conventional control. The findings of the present study suggest that the application of MixOS has the greatest regulation effects on delayed leaf senescence, well-developed roots, and higher fruit productions of strawberry and cucumber. Exogenous MixOS resulted in significant increases in SPAD values, maximum photochemical efficiency (Fv/Fm), and photochemical quenching coefficiency (qP); they were increased by 1.94–28.96%, 5.41–33.89%, and 9.93–62.07%, compared to the CSOS, CM, and CK treatments, respectively. The orderly and steady structure of thylakoids in the chloroplast, and the randomly distributed starch grains, could be clearly observed in the MixOS treatment, while the non-photochemical quenching (NPQ) was correspondingly reduced by 19.04–45.92%. Meanwhile, the remarkable promotion of root activity and root surface morphology indicators (i.e., root length, surface area, average diameter, and volume) could be observed when exposed to the MixOS treatments, and the total yields of strawberry and cucumber were all increased by 12.40–25.57%. These findings suggest that the mixed oligosaccharides mainly promote the coordinated growth of root and shoot, which leads to the improved yields of strawberry and cucumber.

This study focuses on optimizing chlorophyll extraction techniques, in which leaf discs are cut from places on the leaf blade to enhance chlorophyll concentration in sesame (Sesamum indicum L.) leaves. Thirty sesame genotypes, categorized into light green (LG), middle green (MG), and deep green (DG) pigment groups based on leaf coloration, were selected from a larger pool of field-grown accessions. The investigation involved determining optimal Soil Plant Analysis Development (SPAD) value index measurements, quantifying pigment concentrations, exploring extraction solvents, and selecting suitable leaf disk positions. Significant variations in chlorophyll content were observed across genotypes, greenness categories, and leaf disk positions. The categorization of genotypes into DG, MG, and LG groups revealed a correlation between leaf appearance and chlorophyll content. The study highlighted a consistent relationship between carotenoids and chlorophyll, indicating their role in adaptation to warm environments. An examination of leaf disk positions revealed a significant chlorophyll gradient along the leaf blade, emphasizing the need for standardized protocols. Chlorophyll extraction experiments identified DMSO and 96% ethanol, particularly in those incubated for 10 min at 85 °C, as effective choices. This recommendation considers factors like cost-effectiveness, time efficiency, safety, and environmental regulations, ensuring consistent and simplified extraction processes. For higher chlorophyll extraction, focusing on leaf tips and the 75% localization along the sesame leaf blade is suggested, as this consistently yields increased chlorophyll content. Furthermore, our examination revealed significant anatomical variations in the internal structure of the mesophyll tissue leaves between deep green and light green sesame plants, primarily linked to chloroplast density and pigment-producing structures. Our findings, therefore, provide insightful knowledge of chlorophyll gradients and encourage the use of standardized protocols that enable researchers to refine their experimental designs for precise and comparable chlorophyll measurements. The recommended solvent choices ensure reliable outcomes in plant physiology, ecology, and environmental studies.

Elymus nutans Griseb. is a dominant forage in the Qinghai–Tibetan Plateau. However, the combined cold and drought (CD) stress is a major problem inhibiting its growth, development, and yield. Here, the responses of morphological, photosynthetic, osmoregulation levels, and signal transduction under cold, drought, and CD stress were explored. Both cold- and drought-stressed plants showed varying degrees of damage. In addition, CD stress led to more severe damage than single stress, especially in total biomass, photosynthetic capacity, and electron transfer efficiency. The total biomass, net photosynthetic rate, and maximal quantum yield of photosystem II (PSII) photochemistry reduced by 61.47%, 95.80%, and 16.06% in comparison with the control, respectively. Meanwhile, CD stress was accompanied by lower chlorophyll contents, down-regulated expression level of key photosynthetic enzymes (EnRbcS, EnRbcL, and EnRCA), stomatal closure, disrupted chloroplast ultrastructure, and reduced starch content. Furthermore, CD stress induced some adaptability responses in cold- and drought-tolerant E. nutans seedlings. The combined stress provoked alterations in both cold- and drought-related transcription factors and responsive genes. EnCBF12, EnCBF9, EnCBF14, and EnCOR14α were significantly up-regulated under cold or drought stress, and the transcript level of EnCBF3 and EnCBF12 was even 2.94 and 12.59 times higher than control under CD treatment, which indicated the key role of transcription factors activation in coping with CD stress. In addition, the content of soluble sugar, reducing sugar, proline, glycine betaine, and other osmolytes was significantly improved under CD stress. Therefore, we demonstrated that exposure to CD stress led to severe morphological and photosynthetic damage and revealed the acclimation to the cold and drought stress combination via osmotic adjustment and transcription factors activation in the Tibetan wild E. nutans. [ABSTRACT FROM AUTHOR]

As sessile organisms, plants face a wide range of abiotic stresses, with salinity being a significant condition affecting their growth, development, and productivity, particularly in arid and semi-arid regions. This study focused on understanding how salinity impacts Jatropha curcas, an important oilseed plant for the production of biodiesel. By examining the anatomy and ultrastructure of stomata and chloroplasts, we investigated the effects of prolonged salinity stress on J. curcas. This stress led to changes in the stomatal density, stomatal index, and ostiole aperture, which can cause an imbalance of water conductivity in the xylem. Through transmission electron microscopy, we explored the subcellular organization of J. curcas chloroplasts and their contribution to plant photosynthetic efficiency, providing insights into their role in this process. Notably, increases in salinity resulted in a significant increase in starch granule accumulation, leading to impaired granal and stromal grana lamellae, destroying this ultrastructure. Our findings indicate that the anatomy and ultrastructure of chloroplasts play a crucial role in influencing photosynthetic efficiency. Moreover, impaired hydraulic conductivity due to salinity and a lesser osmotic potential in vessels may cause a reduced source-to-sink relationship, which increases starch accumulation in the chloroplast and influences the ultrastructure of the chloroplast. This study offers a new perspective on the structure and function of chloroplasts in J. curcas, presenting innovative opportunities to develop strategies that enhance the production of biofuel in areas with high soil salinity. [ABSTRACT FROM AUTHOR]

Lead nitrate has reports of significantly inhibiting plant growth. Early exploration of the genotypic difference for lead nitrate stress in tobacco has started. The presented study had eight tobacco genotypes subjected to 200 µM lead nitrate (Pb [NO3]2) stress in a hydroponic culture. Lead stress treatment to plants for 14 days had data recording at three times intervals of stressed plants. Assessing photosynthetic and antioxidant enzymes' activities was in a time series order of one day, seven days, and 14 days. One-day, seven-day, and fourteen-day-old seedlings gained treatment of 200 µM lead nitrate stress and control. Soil Plant Analysis Development (SPAD) values for most genotypes decreased, while oxidant and anti-oxidant enzymes increased activity. Chlorophyll-a, chlorophyll-b, and total chlorophyll evaluated after lead nitrate toxicity showed reduced activity in studied tobacco genotypes compared with control as time passed. All chlorophyll contents, i.e., chlorophyll a, b, and total chlorophyll, declined with a longer span in lead nitrate solution. Genotype QVA-20 could benefit lead-salt tolerance and susceptible genotype 'long chang' cigarette based on chlorophyll content and SPAD values. Chlorophyll a capacity decreased as lead exposure to plants increased, but chlorophyll b increased in all genotypes on the 15th day. The MDA (malondialdehyde) content increased in all tobacco genotypes with increased lead nitrate exposure. Meanwhile, SOD (superoxide dismutase) contents decreased in genotypes RG-8, E1, and X6 with increased time, but POD (peroxidase) contents increased in all genotypes on the 14th day. Genotypes RG-8, E1, and X6 proved considerably tolerant of lead toxicity at 200 µM. [ABSTRACT FROM AUTHOR]

The light-sensitive albino tea plant can produce pale-yellow shoots with high levels of amino acids which are suitable to process high-quality tea. In order to understand the mechanism of the albino phenotype formation, the changes in the physio-chemical characteristics, chloroplast ultrastructure, chlorophyll-binding proteins, and the relevant gene expression were comprehensively investigated in the leaves of the light-sensitive albino cultivar 'Huangjinya' ('HJY') during short-term shading treatment. In the content of photosynthetic pigments, the ultrastructure of the chloroplast, and parameters of the photosynthesis in the leaves of 'HJY' could be gradually normalized along with the extension of the shading time, resulting in the leaf color transformed from pale yellow to green. BN-PAGE and SDS-PAGE revealed that function restoration of the photosynthetic apparatus was attributed to the proper formation of the pigment-protein complexes on the thylakoid membrane that benefited from the increased levels of the LHCII subunits in the shaded leaves of 'HJY', indicating the low level of LHCII subunits, especially the lack of the Lhcb1 might be responsible for the albino phenotype of the 'HJY' under natural light condition. The deficiency of the Lhcb1 was mainly subject to the strongly suppressed expression of the Lhcb1.x which might be modulated by the chloroplast retrograde signaling pathway GUN1 (GENOMES UNCOUPLED 1)-PTM (PHD type transcription factor with transmembrane domains)-ABI4 (ABSCISIC ACID INSENSITIVE 4). [ABSTRACT FROM AUTHOR]

Leaves are the most important photosynthetic organs in most woody plants, but chloroplasts are also found in organs optimized for other functions. However, the actual photosynthetic efficiency of these chloroplasts is still unclear. We analyzed bark and wood chloroplasts of Fraxinus ornus L. saplings. Optical and spectroscopic methods were applied to stem samples and compared with leaves. A sharp light gradient was detected along the stem radial direction, with blue light mainly absorbed by the outer bark, and far-red-enriched light reaching the underlying xylem and pith. Chlorophylls were evident in the xylem rays and the pith and showed an increasing concentration gradient toward the bark. The stem photosynthetic apparatus showed features typical of acclimation to a low-light environment, such as larger grana stacks, lower chlorophyll a/b and photosystem I/II ratios compared with leaves. Despite likely receiving very few photons, wood chloroplasts were photosynthetically active and fully capable of generating a light-dependent electron transport. Our data provide a comprehensive scenario of the functional features of bark and wood chloroplasts in a woody species and suggest that stem photosynthesis is coherently optimized to the prevailing micro-environmental conditions at the bark and wood level. [ABSTRACT FROM AUTHOR]

The aim of this study was to examine the effect of the modified light spectrum of glass containing red luminophore on the performance of the photosynthetic apparatus of two types of lettuce cultivated in soil in a greenhouse. Butterhead and iceberg lettuce were cultivated in two types of greenhouses: (1) covered with transparent glass (control) and (2) covered with glass containing red luminophore (red). After 4 weeks of culture, structural and functional changes in the photosynthetic apparatus were examined. The presented study indicated that the red luminophore used changed the sunlight spectrum, providing an adequate blue:red light ratio, while decreasing the red:far-red radiation ratio. In such light conditions, changes in the efficiency parameters of the photosynthetic apparatus, modifications in the chloroplast ultrastructure, and altered proportions of structural proteins forming the photosynthetic apparatus were observed. These changes led to a decrease of CO2 carboxylation efficiency in both examined lettuce types. [ABSTRACT FROM AUTHOR]

Plants evolved in the presence of the Earth's magnetic field (or geomagnetic field, GMF). Variations in MF intensity and inclination are perceived by plants as an abiotic stress condition with responses at the genomic and metabolic level, with changes in growth and developmental processes. The reduction of GMF to near null magnetic field (NNMF) values by the use of a triaxial Helmholtz coils system was used to evaluate the requirement of the GMF for Lima bean (Phaseolus lunatus L.) photosynthesis and reactive oxygen species (ROS) production. The leaf area, stomatal density, chloroplast ultrastructure and some biochemical parameters including leaf carbohydrate, total carbon, protein content and δ13C were affected by NNMF conditions, as were the chlorophyll and carotenoid levels. RubisCO activity and content were also reduced in NNMF. The GMF was required for the reaction center's efficiency and for the reduction of quinones. NNMF conditions downregulated the expression of the MagR homologs PlIScA2 and PlcpIScA, implying a connection between magnetoreception and photosynthetic efficiency. Finally, we showed that the GMF induced a higher expression of genes involved in ROS production, with increased contents of both H2O2 and other peroxides. Our results show that, in Lima bean, the GMF is required for photosynthesis and that PlIScA2 and PlcpIScA may play a role in the modulation of MF-dependent responses of photosynthesis and plant oxidative stress. [ABSTRACT FROM AUTHOR]

Drought hampers agricultural production by constraining crop growth and development. Nevertheless, there has been limited exploration regarding the effect of biochar coating in enhancing seed germination under drought conditions and understanding its underlying mechanisms. To fill this gap and clarify the pathway to drought resistance, the current research investigated the protective effectiveness of BC on seedling establishment and subsequent growth of rice under drought conditions. Results showed that BC notably elevated emergence rate (5.5%), shoot length (27.4%), root length (33.4%), plant height (19.6/10.3%), leaf area (69.8/71.7%), and plant biomass (85.7/67.9%) after 15/30 days under drought conditions compared to the control. Biochar coating facilitated the maintenance of a stable chloroplast structure, reduced chlorophyll degradation, and sustained cell expansion. This contributed to the improvement of stomatal characteristics on both adaxial and abaxial leaf surfaces during drought stress, encompassing enhancements in stomatal density and aperture. The preservation of stomatal opening led to an increased photosynthetic capacity, thereby fostering elevated photosynthetic activity and heightened plant biomass under stressful conditions. Simultaneously, BC treatment significantly diminished the production of reactive oxygen species, preserved cell membrane integrity, and augmented the accumulation of osmotic protectants. These outcomes signify that biochar coating mitigates the deleterious impacts of drought stress on photosynthesis, stomatal aperture, chloroplast ultrastructure, osmotic regulation, and redox homeostasis in plants through specific water and nutrient regulation. Consequently, this enhances the tolerance and growth of rice under drought stress. • Seed coating with biochar (BC) has emerged as a sustainable solution for crop production and resistance to water shortage. • BC promoted seed germination, stand establishment and subsequent growth of rice plants under drought conditions. • BC improved photosynthetic performance under drought by improving stomatal density and aperture and photosynthetic pigments. • Ultrastructural analysis revealed that BC stabilized the chloroplast structure and protected cell walls under water stress. [ABSTRACT FROM AUTHOR]

Objective: In the future, the stress of enhanced UV-B radiation on the Earth will first affect the photosynthesis of plants, including mangoes. Therefore, it is necessary to study the effects of enhanced UV-B radiation on the photosynthesis of mangoes. Methods: 'Tainong No 1' mango trees in the field were selected as the experimental material and divided into 2 groups: one group was shined under 96 kJ·m−2·d−1 UV-B lamps for artificially simulated treatment of enhanced UV-B radiation, and the other group was shined under sunshine directly as the control (CK). The main photosynthetic physiological indicators were measured with conventional methods, and the expression levels of the genes encoding large and small subunits of the Rubisco enzyme were measured with fluorescent qPCR. The changes in stomatal morphology and chloroplast structure were observed with scanning electron microscopy and transmission electron microscopy. Results: The content of malondialdehyde (MDA) and the relative conductivity in the leaves of the treatment tended to be significantly higher than those of the CK. The net photosynthetic rate (Pn) of the treatment tended to decrease and be lower than that of CK. The dynamics of intercellular CO2 concentration (Ci) of the treatment and CK changed differently from each other but generally tended to decrease, and that of the treatment tended to be significantly higher than that of CK. The stomatal conductance (Gs) of the treatment and CK both generally decreased, and that of the treatment was always significantly lower than that of CK. The contents of chlorophyll a, chlorophyll b and total chlorophyll and the ratio of chlorophyll a/b of the treatment were lower than those of CK, while the carotenoid content showed the opposite trend. The stomata and the surface of leaves of the treatment were sunken and damaged, respectively. The palisade tissue, spongy tissue and upper epidermis thickened more, and the total thickness significantly increased. Meanwhile, the ratio of palisade tissue to spongy tissue decreased. During treatment, the chloroplasts were swollen and shortened, the number of chloroplasts was reduced, the starch grains were degraded, and the grana lamella were distorted, loosely arranged and blurred. The expression of the genes encoding the Rubisco large subunit (rbcL) in the treatment was significantly inhibited, while that encoding the Rubisco small subunit (rbcS) decreased first and increased later. In conclusion, 96 kJ·m−2·d−1 enhanced UV-B radiation treatment caused damage to the leaf cell membrane system. This led to stomatal limitation of photosynthesis by destroying the stomatal structure and nonstomatal limitation of photosynthesis by damaging the submicrostructure of the chloroplasts and downregulating the expression of rbcL. The leaves may resist the photosynthetic damage caused by enhanced UV-B radiation by upregulating rbcS expression as much as possible. [ABSTRACT FROM AUTHOR]

Crop production and growth are severely affected by salt stress. Nevertheless, the bio-fertilizer vermicompost (VC) can be participated as a potent inhibitor of salinity on plant growth and crop production by regulating photosynthetic efficiency. We investigated the effect of VC on photosynthetic performance of salt-stressed broad bean (Vicia faba L. Aspani cultivar). Seeds were grown in soil mixture; clay and sand in ratio 1:2 by volume with five different volumetric ratios of VC; 0, 2.5, 5, 10 and 15% irrigated with either water and/or 200 mM NaCl. Leaf area, Na and K contents, chlorophylls, photosystem II efficiency, Rubisco content, soluble sugars, chloroplasts' organization and proteomics were analyzed. The imposed stress decrease leaf area, chlorophyll contents, maximum quantum efficiency (Fv/Fm), Rubisco content, increase soluble sugars and damage chloroplasts organization. Salinity upregulated glucose-1-phosphate adenylyl transferase, ribulose bisphosphate carboxylase large subunit and chloroplastic peptidyl-prolyl cis–trans isomerase. The increased leaf area, chlorophyll a, b and carotenoids, maximum quantum efficiency of photosystem II, Rubisco content, improving the degeneration of thylakoid lamellae and lessening plastoglobuli number in thylakoid membranes are the major benefits attained with vermicompost treatments under salt stress. Analysis of proteomic revealed that VC upregulated chloroplastic ferredoxin–NADP reductase, plastocyanin, polyphenol oxidase, peptidyl-prolyl cis–trans isomerase, alpha-glucan phosphorylase H isozyme and maturase expression under salt stress. The results suggest that VC controls protein expression at the level of transcriptional and translational which may conserve photosynthetic components and prevent salt-induced harmful effects in broad bean plants. [ABSTRACT FROM AUTHOR]

Key message: The species did not show a response pattern to flooding. Andira anthelmia and Vernonanthura discolor invested in plastic responses, while Guarea guidonia established a balance between integration and phenotypic plasticity. Dense ombrophilous forests are tropical phytophysiognomies that make up the vegetation mosaic of the Brazilian Atlantic Forest. These forests occur in humid regions and often contain flooded areas that impose obstacles to plant colonization. Some species such as Guarea guidonia (Meliaceae), Andira anthelmia (Fabaceae), and Vernonanthura discolor (Asteraceae) can tolerate these flooding conditions. However, little is known about the acclimatization of these species to flooding. For this reason, morphoanatomical and physiological analyses were performed on the leaves of five individuals of each species selected from a flooded and non-flooded site. The results showed that the species presented thicker leaves and higher specific leaf mass values under flooding conditions. However, it was observed that the thickening of G. guidonia and V. discolor is mainly influenced by the palisade parenchyma thickness, while in A. anthelmia thickening was more closely related to the spongy parenchyma thickness. Greater thickening of the cuticle and epidermis and greater density of stomata were also observed in the flooded site. The chlorophyll a and b and carotenoid contents were significantly lower in the flooded site. Chloroplasts exhibited higher amounts of starch grain, lipid drops, and plastoglobules in the flooded site. Regarding the quantum yield of photosystems II, only A. anthelmia showed a reduction in Fv/Fm values in the flooded site. Plasticity and phenotypic integration analyses made it possible to conclude that the acclimatization of A. anthelmia and V. discolor was mainly mediated by plastic adjustments. At the same time, G. guidonia presented greater phenotypic integration. [ABSTRACT FROM AUTHOR]

The vital signaling molecule 5-Aminolevulinic acid (ALA) plays critical roles in signal transduction and biological modulation under abiotic stresses. In this study, we explored the effects of exogenous ALA on low-light (LL) stress-induced photosynthesis and antioxidant system damage in tall fescue (Festuca arundinacea Schreb.) seedlings. LL stress decreased morphological index values and chlorophyll contents, while also reduced net photosynthetic rate (Pn) and the maximum quantum yield of photosystem II photochemistry (F v / F m). Notably, these restrictions were substantially alleviated by exogenous ALA. Moreover, the contents of chlorophyll and its synthetic precursors were significantly increased after ALA treatment. Meanwhile, ALA observably enhanced expression level of FaCHLG , FaHEMA , FaPOR , and FaCAO , which encode the chlorophyll precursors biosynthesis enzymes. Exogenous ALA repaired the damage to the chloroplast ultrastructure caused by LL stress and promoted the formation of ordered thylakoids and grana lamella. ALA also improved Rubisco activity and expression level of the photosynthetic enzyme genes FaRuBP , FaPRK , and FaGADPH. Additionally, application of exogenous ALA decreased relative electrolytic leakage and the accumulation of malondialdehyde (MDA), hydrogen peroxide (H 2 O 2), and superoxide radicals (O 2 ∙-), and increased the gene expression levels and activity of antioxidant enzymes. The ratios of ascorbic acid (AsA) to dehydroascorbic acid (DHA) and reduced glutathione (GSH) to oxidized glutathione (GSSG) were also increased significantly by application of ALA. Furthermore, all responses could be reversed by treatment with levulinic acid (LA). Thus, these results indicated that ALA protects tall fescue from LL stress through scavenging ROS, improving photosynthetic enzyme activity levels, increasing photosynthetic pigments contents, repairing chloroplast damage, and enhancing the photosynthesis rate. • ALA repaired the damage to the chloroplast ultrastructure caused by low-light (LL) stress. • ALA activated enzymic antioxidant system and AsA-GSH cycle to remove excess ROS. • ALA promoted the chlorophyll biosynthesis pathway to enhancing photosynthetic pigment contents. • ALA enhanced photosynthetic performance to keep a high photosynthesis level under LL stress. [ABSTRACT FROM AUTHOR]

Nanotechnologies provide a great platform for researching nanoparticles effects on living organisms including plants. This work shows the stimulating effect of seed priming with gold nanoparticles (AuNPs) on photosynthetic apparatus of Triticum aestivum seedlings. It was found using inductively coupled plasma-atomic emission and mass spectrometry that AuNPs (the average diameter of 15.3 nm, concentration of 20 μg ml−1) penetrated into the seeds, but were not found in seedling leaves. Ultrastructural changes in chloroplasts were found using transmission electron microscopy in plants grown from treated seeds: increases in the size of plastids, starch grains, grana in chloroplasts, and the number of thylakoids in grana. The intensity of photosynthesis, the content of chlorophylls, and the portion of unsaturated fatty acids in the composition of total leaf lipids were increased in treated AuNPs plants. This study demonstrates that revealed changes determined the increased tolerance of wheat to low temperature. The adaptive significance of these changes, possible mechanisms of the AuNPs effects on plants and future perspectives of study are discussed. This is the first report showing nanopriming with AuNPs as a new method to study the mechanisms of stress tolerance. • Priming with AuNPs is a trigger of wheat chloroplasts ultrastructural reorganization. • Seed priming with AuNPs increases photosynthesis and chlorophylls content of wheat. • Fatty acids composition in wheat leaves changed after AuNPs treatment. • Seed priming with AuNPs increases cold tolerance of wheat plants. [ABSTRACT FROM AUTHOR]

Nanjing 5718 is a rice variety with good eating quality approved by Jiangsu province in 2019 and was confirmed as super rice by the Ministry of Agriculture and Rural affairs in 2021. Studying its yield composition characteristics, photosynthetic characteristics, and physiological basis can be helpful to investigate photosynthetic traits of super rice variety, improve its photo- synthetic performance through genetic improvement, and provide the theoretical basis for high-yield breeding and cultivation of japonica rice. In this study, the parents of Nanjing 5718 and Huaidao 5, a widely popularized rice variety with the same growth period type, as the control, dry weight of aboveground of plant, chlorophyll contents, photosynthetic rates, and photochemical characteristics of photosystem II (PSII), core antenna protein expression, photosynthetic enzyme activities, and chloroplast ultrastructure were investigated in Nanjing 5718 from full expansion of flag leaves at the beginning of booting to 35 days after flowering. The results showed the pigment contents of the leaves in Nanjing 5718 were higher, which were close to male parent Yanjing 608. The net photosynthetic rates, dry weight, and PSII electron transfer activities of flag leaves at the late growth stage were significantly higher in Nanjing 5718 than those in parents and Huaidao 5. The light energy conversion performance of PSII was superior. The core antenna protein CP43 and CP47 were more stable under strong light and high temperature, and their adjustment ability of Nanjing 5718 was better than that of parents and Huaidao 5. In addition, the activities of RuBP carboxylase in flag leaves were higher, the contents of photosynthetic products were higher, the chloroplast structure was more stable, the senescence characteristics appeared later, and the chloroplast decay rates were slower in Nanjing 5718, compared with parents and Huaidao 5. The results indicated that high photosynthetic performance of flag leaves was the basis for the formation of high yield characteristics of super rice Nanjing 5718 with large panicles. The great activity and function of photosystem proteins were main factors of improving leaf photosynthesis, and the stability of chloroplast structure could provide powerful support for high photosynthetic efficiency of leaves. [ABSTRACT FROM AUTHOR]

To date, only a few submerged plants have been reported to perform C 4 and CAM. Ottelia cordata is a heteroblastic aquatic plant developing both submerged and floating leaves throughout its life cycle. Previous research found that, besides HCO 3 - use, the submerged leaves of O. cordata can also perform C 4 metabolism. However, it remains unclear how the HCO 3 - use or the C 4 pathway, and the anatomical structure, respond to varying CO 2 environments. Therefore, we examined the anatomical structures and carbon-concentrating mechanisms in O. cordata submerged leaves under high (HC) and low CO 2 (LC) conditions. Our results revealed the leaf consists of an upper and lower layer of epidermal cells, separated by large air spaces and two layers of mesophyll cells, without the presence of Kranz anatomy. Both epidermal and mesophyll cells contained chloroplasts, but starch grains were larger in the mesophyll chloroplasts than in the epidermal cells. Additionally, the area of the upper epidermal cells, mesophyll cells, air spaces, chloroplast, and starch grains significantly increased under HC. Moreover, the ability to utilize HCO 3 - was stronger under LC. The activity of photosynthetic enzymes, kinetics of O 2 evolution, and δ 13 C confirmed the C 4 pathway under both HC and LC. However, the organic acid results indicated that CAM was not operational in either HC or LC. In summary, our findings suggested that the ability to use HCO 3 - and a C 4 -like metabolism may occur in the submerged leaves of O. cordata, despite the absence of Kranz anatomy, across both HC and LC environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Masson SAS. All rights reserved.)

Abstract Background Melatonin played an essential role in numerous vital life processes of animals and captured the interests of plant biologists because of its potent role in plants as well. As far as its possible contribution to photoperiodic processes, melatonin is believed to act as a growth regulator and a direct free radical scavenger/indirect antioxidant. The objective of this study to identify a precise melatonin concentration for a particular application method to improve plant growth requires identification and clarification. Methods This work establishes unique findings by optimizing melatonin concentration in alleviating the detrimental effects of drought stress in maize. Maize plants were subjected to drought stress (40–45% FC) after treatments of melatonin soil drenching at different concentrations (50, 100, and 150 µM) to consider the changes of growth attribute, chlorophyll contents, photosynthetic rate, relative water content (RWC), chloroplast ultrastructure, endogenous hormonal mechanism, and grain yield. Results Our results showed that the application of melatonin treatments remarkably improved the plant growth attributes, chlorophyll contents, photosynthetic rate, RWC, hormonal mechanism, and grain yield plant−1 under drought conditions at a variable rate. Conclusion Our current findings hereby confirmed the mitigating potential of melatonin application 100 µM for drought stress by maintaining plant growth, hormone content, and grain yield of maize. We conclude that the application of melatonin to maize is effective in reducing drought stress tolerance. Graphical Abstract

Elymus nutans Griseb. is a dominant forage in the Qinghai–Tibetan Plateau. However, the combined cold and drought (CD) stress is a major problem inhibiting its growth, development, and yield. Here, the responses of morphological, photosynthetic, osmoregulation levels, and signal transduction under cold, drought, and CD stress were explored. Both cold- and drought-stressed plants showed varying degrees of damage. In addition, CD stress led to more severe damage than single stress, especially in total biomass, photosynthetic capacity, and electron transfer efficiency. The total biomass, net photosynthetic rate, and maximal quantum yield of photosystem II (PSII) photochemistry reduced by 61.47%, 95.80%, and 16.06% in comparison with the control, respectively. Meanwhile, CD stress was accompanied by lower chlorophyll contents, down-regulated expression level of key photosynthetic enzymes (EnRbcS, EnRbcL, and EnRCA), stomatal closure, disrupted chloroplast ultrastructure, and reduced starch content. Furthermore, CD stress induced some adaptability responses in cold- and drought-tolerant E. nutans seedlings. The combined stress provoked alterations in both cold- and drought-related transcription factors and responsive genes. EnCBF12, EnCBF9, EnCBF14, and EnCOR14α were significantly up-regulated under cold or drought stress, and the transcript level of EnCBF3 and EnCBF12 was even 2.94 and 12.59 times higher than control under CD treatment, which indicated the key role of transcription factors activation in coping with CD stress. In addition, the content of soluble sugar, reducing sugar, proline, glycine betaine, and other osmolytes was significantly improved under CD stress. Therefore, we demonstrated that exposure to CD stress led to severe morphological and photosynthetic damage and revealed the acclimation to the cold and drought stress combination via osmotic adjustment and transcription factors activation in the Tibetan wild E. nutans.

Phosphate (Pi) deficiency is a common phenomenon in agricultural production and limits plant growth. Recent work showed that long-term Pi deficiency caused the inhibition of photosynthesis and inefficient electron transport. However, the underlying mechanisms are still unknown. In this study, we used the physiological, histochemical, and transcriptomic methods to investigate the effect of low-Pi stress on photosynthetic gas exchange parameters, cell membrane lipid, chloroplast ultrastructure, and transcriptional regulation of key genes in melon seedlings. The results showed that Pi deficiency significantly downregulated the expression of aquaporin genes, induced an increase in ABA levels, and reduced the water content and free water content of melon leaves, which caused physiological drought in melon leaves. Therefore, gas exchange was disturbed. Pi deficiency also reduced the phospholipid contents in leaf cell membranes, caused the peroxidation of membrane lipids, and destroyed the ultrastructure of chloroplasts. The transcriptomic analysis showed that 822 differentially expressed genes (DEGs) were upregulated and 1254 downregulated by Pi deficiency in leaves. GO and KEGG enrichment analysis showed that DEGs significantly enriched in chloroplast thylakoid membrane composition (GO:0009535), photosynthesis-antenna proteins (map00196), and photosynthesis pathways (map00195) were downregulated by Pi deficiency. It indicated that Pi deficiency regulated photosynthesis-related genes at the transcriptional level, thereby affecting the histochemical properties and physiological functions, and consequently causing the reduced light assimilation ability and photosynthesis efficiency. It enriches the mechanism of photosynthesis inhibition by Pi deficiency. [ABSTRACT FROM AUTHOR]

Malus spectabilis 'Duojiao' is a spontaneous delayed-green leaf color mutant of M. spectabilis 'Riversii' and has chloroplasts with irregularly arranged vesicles and indistinct stromal lamellae. The yellow leaves of mutant have less chlorophyll (Chl), carotenoids, and flavonoids. Measurement of photosynthetic gas exchange indicated that the mutant has lower photosynthetic activity than 'Riversii' plants. Transcriptome sequencing with the Illumina platform was used to characterize differences in gene expression between the leaves of plants with yellow and green colors and elucidate the molecular mechanisms responsible for variation in leaf color in ornamental crabapple. In the comparison group of mutant yellow leaves and the maternal green leaves, 1848 differentially significant expressed genes (DEGs) were annotated by transcriptomic analysis. Many DEGs and transcription factors were identified related to chloroplast development, Chl synthesis and degradation, photosynthesis, carotenoid biosynthesis, flavonoid biosynthesis and other pathways related to plant leaf color formation. Among these, the Chl biosynthesis-related coproporphyrinogen gene, oxidative decarboxylase gene, and Chl a oxygenase gene were down-regulated, indicating that Chl biosynthesis was blocked. GLK1, which regulates chloroplast development, was down-regulated in yellow leaves. Parallel experiments showed that the content of the Chl synthesis precursors, protoporphyrinogen IX, chlorophyllide a, and chlorophyllide b and the activity of chlorophyllogen III oxidase and chlorophyllide a oxygenase in the yellow leaves of 'Duojiao' were lower than those in the green leaves of 'Riversii'. Thus, leaf color formation is greatly affected by Chl metabolism and chloroplast development. The reliability of the RNA-sequencing data was confirmed by quantitative real-time PCR analysis with 12 selected DEGs. [ABSTRACT FROM AUTHOR]

Iris tectorum Maxim. is an important plant that plays a very crucial role in the ecological welfare of wetlands. In this study, the effects of different intensities of UV-B radiation on the growth, photosynthetic pigment content, chlorophyll fluorescence characteristics, chloroplast ultrastructure, and gas exchange parameters of Iris tectorum Maxim. were studied. The results showed that enhanced UV-B radiation had a significant influence on the above-mentioned parameters of iris. Compared with the control, enhanced UV-B radiation caused certain damage to the leaf appearance. With the increasing intensity of radiation, the apparent damage degree became more serious. Enhanced UV-B radiation significantly decreased leaf chlorophyll contents, and the effect accumulated with the exposure time. Enhanced UV-B radiation increased Fo, significantly increased the non-photochemical quenching coefficient NPQ, reduced PSII and Qp, and significantly decreased the Fm, Fv/Fm, and Fv/Fo in leaves. The effect of UV-B radiation on PSII destruction of Iris tectorum Maxim. increased as the radiation intensity increased and the exposure time prolonged. The chloroplast structure was damaged under the enhanced UV-B radiation. More specifically, thylakoid lamellae were distorted, swelling and even blurred, and a large number of starch granules appeared. The effect of the high intensity of radiation on chloroplast ultrastructure was greater than that of lower intensity. Enhanced UV-B radiation reduced significantly the net photosynthetic rate, stomatal conductance, and transpiration rate, and the degree of degradation increased with the increasing irradiation intensity. However, the intercellular CO2 content increased, which suggests that the main reason for the decrease of photosynthetic rate was the non-stomatal factors. [ABSTRACT FROM AUTHOR]

Copyright of Shipin Kexue/ Food Science is the property of Food Science Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Compared with only the salt-treated plants, all of these growth parameters of Si-treated plants were improved in both cotton genotypes, indicating a positive effect of Si on enhancing salt tolerance of cotton. Keywords: salinity; silicon; chloroplast ultrastructure; antioxidant enzymes; photosynthetic performance EN salinity silicon chloroplast ultrastructure antioxidant enzymes photosynthetic performance N.PAG N.PAG 20 08/29/22 20220801 NES 220801 1. Since plant roots only absorb mono silicic acid (Si (OH) SB 4 sb , pH < 9), and Si in the soil is mainly in the form of silicate or aluminum silicate, exogenous Si as fertilizer is applied despite the abundant Si in soil [[11], [21]]. The application of the Si fertilizer markedly lowered the K-point fluorescence value of the salt-stressed cotton seedling (Figure 9D and Figure 10E), indicating that Si can alleviate the damage of oxygen-evolving complexes caused by salt stress to a certain extent, and relieve the suppression of the photosynthetic electron production and transport due to salt stress [[44]]. [Extracted from the article]

The grey mangrove, Avicennia marina, is frequently threatened by extreme salinity resulting from the reduced tidal influence and high water evaporation in warm regions throughout the world. This study assessed the effects of high salinity (900 mM NaCl) on A. marina seedlings under controlled conditions after 30 days of treatment. Plant dry weight and the net photosynthetic rate slightly reduced by the high salinity. Leaf water status, the intrinsic water use efficiency and internal CO2 concentration were enhanced. Sodium and chloride were preferentially accumulated in roots and stems. Thicknesses of the hypodermis, palisade mesophyll, vessel diameter, vessel wall, and palisade mesophyll cell layers increased under high salinity. The entire lamina and the spongy mesophyll thicknesses maintained invariant. Chloroplasts from palisade mesophyll cells were adequately preserved; grana stacks were visible, intergranal lamellae and thylakoids were visible and linear, and starch grains were large. In contrast, some of the spongy mesophyll chloroplasts were swollen and damaged. Our results showed that the facultative halophyte A. marina has a significant ability to protect leaf anatomy, palisade mesophyll chloroplasts ultrastructure and photosynthesis process under high salinity, which profoundly contributes to its high salt tolerance. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan Agricultural Sciences is the property of Editorial Board of Journal of Henan Agricultural Sciences and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this study was to examine the effect of the modified light spectrum of glass containing red luminophore on the performance of the photosynthetic apparatus of two types of lettuce cultivated in soil in a greenhouse. Butterhead and iceberg lettuce were cultivated in two types of greenhouses: (1) covered with transparent glass (control) and (2) covered with glass containing red luminophore (red). After 4 weeks of culture, structural and functional changes in the photosynthetic apparatus were examined. The presented study indicated that the red luminophore used changed the sunlight spectrum, providing an adequate blue:red light ratio, while decreasing the red:far-red radiation ratio. In such light conditions, changes in the efficiency parameters of the photosynthetic apparatus, modifications in the chloroplast ultrastructure, and altered proportions of structural proteins forming the photosynthetic apparatus were observed. These changes led to a decrease of CO2 carboxylation efficiency in both examined lettuce types.

Short-term assessment of adverse effects is essential for populations exposed to higher risk of environmental pollution. This study presents the time course of physiological and morphological changes attributed to cadmium, emphasizing age-linked differences in the susceptibility of photosynthetic apparatus of Spirodela polyrhiza fronds exposed to different cadmium concentrations. A four-frond colony represented by mother, daughter, and granddaughter plants was exposed to cadmium concentrations for 6, 24, and 72 h to establish its effect on different generations of the great duckweed. The duration of cadmium exposure accounted for the most variation in chlorophyll content as the most influential variable, and after 72 h, frond responsiveness was a function of cadmium concentration. Carotenoid contents behaved slightly differently in fronds of different ages, with the oldest mother frond exhibiting accelerated senescence. Chlorophyll fluorescence measurements showed that cadmium affects different photosynthetic electron transport segments relative to the frond's chloroplast structure level. Photosynthesis of mother fronds exposed to low cadmium and daughter fronds exposed to high cadmium was determined by the functionality of primary electron acceptance at the PSII level. Mother plants exposed to higher cadmium concentrations were characterized by closed and inactive reaction centers, dissipated energy outflux, and inhibited photosynthesis. Young fronds exposed to low and high cadmium concentrations were characterized by increased non-reducing reaction centers and thermal phase reduction, with activated dissipative mechanisms at high cadmium concentrations. Cadmium-induced changes in the ultrastructure of chloroplasts were visible after 6 h of exposure to lowest concentrations, with gradual degradation of the thylakoid system as the fronds aged. Younger fronds responded to cadmium more dynamically through molecular, physiological, and anatomical changes and tolerated a more reduced electron transport chain under given conditions than older fronds. [ABSTRACT FROM AUTHOR]

Photosynthesis is crucial for the survival of all living biota, playing a key role in plant productivity by generating the carbon skeleton that is the primary component of all biomolecules. Salinity stress is a major threat to agricultural productivity and sustainability as it can cause irreversible damage to photosynthetic apparatus at any developmental stage. However, the capacity of plants to become photosynthetically active under adverse saline conditions remains largely untapped. This study addresses this discrepancy by exploring the current knowledge on the impact of salinity on chloroplast operation, metabolism, chloroplast ultrastructure, and leaf anatomy, and highlights the dire consequences for photosynthetic machinery and stomatal conductance. We also discuss enhancing photosynthetic capacity by modifying and redistributing electron transport between photosystems and improving photosystem stability using genetic approaches, beneficial microbial inoculations, and root architecture changes to improve salt stress tolerance under field conditions. Understanding chloroplast operations and molecular engineering of photosynthetic genes under salinity stress will pave the way for developing salt-tolerant germplasm to ensure future sustainability by rehabilitating saline areas. • Plant capacity to become photosynthetically active under salinity remains largely untapped. • Modifying electron transport and photosystem stability improve photosynthesis under salinity. • Using beneficial microbial and root architecture changes enhance salt tolerance. • Engineering of photosynthetic genes may help developing salt-tolerant plant genotypes. [ABSTRACT FROM AUTHOR]

Short-term assessment of adverse effects is essential for populations exposed to higher risk of environmental pollution. This study presents the time course of physiological and morphological changes attributed to cadmium, emphasizing age-linked differences in the susceptibility of photosynthetic apparatus of Spirodela polyrhiza fronds exposed to different cadmium concentrations. A four-frond colony represented by mother, daughter, and granddaughter plants was exposed to cadmium concentrations for 6, 24, and 72 h to establish its effect on different generations of the great duckweed. The duration of cadmium exposure accounted for the most variation in chlorophyll content as the most influential variable, and after 72 h, frond responsiveness was a function of cadmium concentration. Carotenoid contents behaved slightly differently in fronds of different ages, with the oldest mother frond exhibiting accelerated senescence. Chlorophyll fluorescence measurements showed that cadmium affects different photosynthetic electron transport segments relative to the frond's chloroplast structure level. Photosynthesis of mother fronds exposed to low cadmium and daughter fronds exposed to high cadmium was determined by the functionality of primary electron acceptance at the PSII level. Mother plants exposed to higher cadmium concentrations were characterized by closed and inactive reaction centers, dissipated energy outflux, and inhibited photosynthesis. Young fronds exposed to low and high cadmium concentrations were characterized by increased non-reducing reaction centers and thermal phase reduction, with activated dissipative mechanisms at high cadmium concentrations. Cadmium-induced changes in the ultrastructure of chloroplasts were visible after 6 h of exposure to lowest concentrations, with gradual degradation of the thylakoid system as the fronds aged. Younger fronds responded to cadmium more dynamically through molecular, physiological, and anatomical changes and tolerated a more reduced electron transport chain under given conditions than older fronds.

One of the major detrimental factors of the global rice production is salt stress, which limits it up to 50%. In this study, we compared the morphophysiological and biochemical responses of indigenous salt-tolerant 'Korgut' and salt-sensitive 'Jaya' rice (Oryza sativa L.) varieties by pot culture in controlled climatic conditions. Decreased plant growth and biomass with the increase in salinity were recorded in the 'Jaya' variety compared to those of 'Korgut'. Net photosynthesis rate (PN), transpiration rate (E), stomatal conductance (gs), internal CO2 concentration (Ci), photochemical quenching, and lower quantum efficiency of PSII system (Fv/Fm ratio) were recorded reduced in 'Jaya' compared to those of 'Korgut' as response to salinity stress. Unlike 'Korgut' that thrived well under increased salinity levels, higher concentration (160 mmol/L) of NaCl caused a decrease in the number of thylakoids. In addition, swelling of the thylakoids was observed in 'Jaya'in response to higher salt stress. The tolerance of 'Korgut' plants was mainly due to relatively lesser accumulation of Na+ and Cl- and higher accumulation of K+. 'Korgut' showed relatively higher antioxidant capacity, lower osmotic stress (proline), and oxidative damage (lipid peroxidation) compared to salt-sensitive variety 'Jaya'. Our data suggests that 'Korgut' plants preserve ion and water homeostasis and diminish oxidative stress resulting from more significant antioxidant enzymes, which enables better sustainable growth overcoming salinity stress, contrary to salt-sensitive 'Jaya' variety. These findings can support crop development in terms of salt tolerance in rice crops by the method of molecular genetics. [ABSTRACT FROM AUTHOR]

In recent years, with the global climate change, the intensity, frequency and duration of drought have increased significantly, which has become the main limiting factor for agricultural development in many areas. Glycine betaine (GB) is an effective stress-resistant substance. In this experiment, the effects of the genetic engineering of GB synthesis on photosynthetic apparatus of tobacco under drought stress were studied using transgenic tobacco (T) accumulating GB and wild-type tobacco (K326, WT). Potted tobaccos were subjected to drought stress (controlled irrigation, 25 °C ± 1 °C, a relative humidity: 75–80%) for 9 days, photosynthetic gas exchange parameters, chlorophyll a fluorescence, structure of chloroplast and thylakoid membrane, and protein function of thylakoid membrane were examined under different drought stress time (days). The results showed that T tobacco could accumulate GB and the accumulated GB improved the resistance of the photosynthetic apparatus to drought stress. Under drought stress, the damage of chloroplast and thylakoid lamellae in T tobacco was less than that in WT tobacco, the accumulation of GB in T tobacco could maintain the stability of thylakoid membrane, improved the unsaturated fatty acid index (IUFA) of thylakoid membrane lipid, increased the contents of digalactosyl diacylglycerol (DGDG) and phosphatidylglycerol (PG), and decreased the ratio of monogalactosyl diaylglycerol (MGDG) to DGDG. In addition, under drought stress, the accumulation of GB in T tobacco alleviated the photo-inhibition of PSII, and the increase of xanthophyll cycle de-epoxidation may be one of the reasons for the enhancement of PSII function. [ABSTRACT FROM AUTHOR]

Abstract Background Glycine soja is a halophytic soybean native to saline soil in Yellow River Delta, China. Photosystem I (PSI) performance and the interaction between photosystem II (PSII) and PSI remain unclear in Glycine soja under salt stress. This study aimed to explore salt adaptability in Glycine soja in terms of photosystems coordination. Results Potted Glycine soja was exposed to 300 mM NaCl for 9 days with a cultivated soybean, Glycine max, as control. Under salt stress, the maximal photochemical efficiency of PSII (Fv/Fm) and PSI (△MR/MR0) were significantly decreased with the loss of PSI and PSII reaction center proteins in Glycine max, and greater PSI vulnerability was suggested by earlier decrease in △MR/MR0 than Fv/Fm and depressed PSI oxidation in modulated 820 nm reflection transients. Inversely, PSI stability was defined in Glycine soja, as △MR/MR0 and PSI reaction center protein abundance were not affected by salt stress. Consistently, chloroplast ultrastructure and leaf lipid peroxidation were not affected in Glycine soja under salt stress. Inhibition on electron flow at PSII acceptor side helped protect PSI by restricting electron flow to PSI and seemed as a positive response in Glycine soja due to its rapid recovery after salt stress. Reciprocally, PSI stability aided in preventing PSII photoinhibition, as the simulated feedback inhibition by PSI inactivation induced great decrease in Fv/Fm under salt stress. In contrast, PSI inactivation elevated PSII excitation pressure through inhibition on PSII acceptor side and accelerated PSII photoinhibition in Glycine max, according to the positive and negative correlation of △MR/MR0 with efficiency that an electron moves beyond primary quinone and PSII excitation pressure respectively. Conclusion Therefore, photosystems coordination depending on PSI stability and rapid response of PSII acceptor side contributed to defending salt-induced oxidative stress on photosynthetic apparatus in Glycine soja. Photosystems interaction should be considered as one of the salt adaptable mechanisms in this halophytic soybean.

Abstract Background The optimized illumination of plants using light-emitting diodes (LEDs) is beneficial to their photosynthetic performance, and in recent years, LEDs have been widely used in horticultural facilities. However, there are significant differences in the responses of different crops to different wavelengths of light. Thus, the influence of artificial light on photosynthesis requires further investigation to provide theoretical guidelines for the light environments used in industrial crop production. In this study, we tested the effects of different LEDs (white, W; blue, B; green, G; yellow, Y; and red, R) with the same photon flux density (300 μmol/m2·s) on the growth, development, photosynthesis, chlorophyll fluorescence characteristics, leaf structure, and chloroplast ultrastructure of Welsh onion (Allium fistulosum L.) plants. Results Plants in the W and B treatments had significantly higher height, leaf area, and fresh weight than those in the other treatments. The photosynthetic pigment content and net photosynthetic rate (P n) in the W treatment were significantly higher than those in the monochromatic light treatments, the transpiration rate (E) and stomatal conductance (G s) were the highest in the B treatment, and the intercellular CO2 concentration (C i) was the highest in the Y treatment. The non-photochemical quenching coefficient (NPQ) was the highest in the Y treatment, but the other chlorophyll fluorescence characteristics differed among treatments in the following order: W > B > R > G > Y. This includes the maximum photochemical efficiency of photosystem II (PSII) under dark adaptation (Fv/Fm), maximum photochemical efficiency of PSII under light adaptation (Fv′/Fm′), photochemical quenching coefficient (qP), actual photochemical efficiency (ΦPSII), and apparent electron transport rate (ETR). Finally, the leaf structure and chloroplast ultrastructure showed the most complete development in the B treatment. Conclusions White and blue light significantly improved the photosynthetic efficiency of Welsh onions, whereas yellow light reduced the photosynthetic efficiency.

Background: Melatonin played an essential role in numerous vital life processes of animals and captured the interests of plant biologists because of its potent role in plants as well. As far as its possible contribution to photoperiodic processes, melatonin is believed to act as a growth regulator and a direct free radical scavenger/indirect antioxidant. The objective of this study to identify a precise melatonin concentration for a particular application method to improve plant growth requires identification and clarification. Methods: This work establishes unique findings by optimizing melatonin concentration in alleviating the detrimental effects of drought stress in maize. Maize plants were subjected to drought stress (40–45% FC) after treatments of melatonin soil drenching at different concentrations (50, 100, and 150 µM) to consider the changes of growth attribute, chlorophyll contents, photosynthetic rate, relative water content (RWC), chloroplast ultrastructure, endogenous hormonal mechanism, and grain yield. Results: Our results showed that the application of melatonin treatments remarkably improved the plant growth attributes, chlorophyll contents, photosynthetic rate, RWC, hormonal mechanism, and grain yield plant−1 under drought conditions at a variable rate. Conclusion: Our current findings hereby confirmed the mitigating potential of melatonin application 100 µM for drought stress by maintaining plant growth, hormone content, and grain yield of maize. We conclude that the application of melatonin to maize is effective in reducing drought stress tolerance. [ABSTRACT FROM AUTHOR]

• Application of Spermidine and Brassinosteroid on maize seedling under waterlogging stress. • Spermidine and Brassinosteroid boosted maize seedling tolerance to waterlogging stress. • Through regulation of root anatomy and enhanced antioxidant defense systems. • By protecting the leaf photosynthetic machinery and chloroplast structure. Frequent flooding and waterlogging adversely impair maize production in China mainly; maize seedlings are extremely sensitive to waterlogging stress at early growth stages. Therefore, improving the resistance of maize seedlings under waterlogging stress is essential for maize production. This study investigated the effects of exogenous spermidine (Spd) and brassinolide (BRs) application on maize seedling adaptation to severe waterlogging. Maize cultivar Xingken-6 (XK-6) was used and treated with Spd (1.5 mg L−1) and BRs (1.0 mmol L−1) under 14-days waterlogging treatments at three-leaf (V3) and fifth-leaf (V5) stages. We found that waterlogging stress decreased overall maize seedling growth by increasing oxidative damage due to reactive oxygen species (ROS) accumulation, decreased photosynthetic capacity, chlorophyll concentration, and significantly damaged chloroplast structure and root anatomy. Spd and BRs treatments effectively relieved impairment of waterlogging by increasing root dry matter (DM), shoot DM, root length, root volume, number of living cortical cells in seminal roots, and net photosynthetic rate. On the other hand, Spd and BRs decreased root aerenchyma area and ROS production across growth stages. Our results demonstrated that Spd and BRs enhanced maize seedling tolerance to waterlogging stress by simultaneously regulating root anatomical structures, photosynthetic machinery, and antioxidant defense systems. [ABSTRACT FROM AUTHOR]