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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., 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.)

Although excess ammoniacal-nitrogen (NH 4 + -N) results in the disturbance of various important biochemical and physiological processes, a detailed study on the effects of NH 4 -N on physiological parameters in Hydrilla verticillata (L.f.) Royle, a submerged macrophyte were investigated, including the contents of photosynthetic pigments, soluble sugars, net photosynthesis and respiration, glutamine synthetase (GS) and glutamate synthase (GOGAT) activities, chloroplast ultrastructure, chloroplast reactive oxygen species (ROS) accumulation and protein levels. Our results showed that the net photosynthetic rate and pigment content reached maximum values when the plants were treated with 1 and 2 mg L + -N stress on the photosynthesis and global changes in protein levels in submerged macrophytes is still lacking. Here, the changes of excess NH 4 + -N on physiological parameters in Hydrilla verticillata (L.f.) Royle, a submerged macrophyte were investigated, including the contents of photosynthetic pigments, soluble sugars, net photosynthesis and respiration, glutamine synthetase (GS) and glutamate synthase (GOGAT) activities, chloroplast ultrastructure, chloroplast reactive oxygen species (ROS) accumulation and protein levels. Our results showed that the net photosynthetic rate and pigment content reached maximum values when the plants were treated with 1 and 2 mg L -1 NH 4 + -N as a control, ROS generation in chloroplasts significantly increased in the presence of more than 2 mg L 4 + -N. Consistently, the damages caused by over-accumulated ROS were observed in chloroplast ultrastructure, showing a loose thylakoid membranes and swollen grana/stroma lamellae. Furthermore, through proteomic analysis, we identified 91 differentially expressed protein spots. Among them, six proteins involved in photosynthesis decreased in abundance in response to excess NH -1 . This decrease might be caused by ROS accumulation. Compared that in 0.02 mg L -1 NH 4 + -N as a control, ROS generation in chloroplasts significantly increased in the presence of more than 2 mg L -1 NH 4 + -N. Consistently, the damages caused by over-accumulated ROS were observed in chloroplast ultrastructure, showing a loose thylakoid membranes and swollen grana/stroma lamellae. Furthermore, through proteomic analysis, we identified 91 differentially expressed protein spots. Among them, six proteins involved in photosynthesis decreased in abundance in response to excess NH 4 + -N. Surprisingly, the abundance of all the identified proteins that were involved in nitrogen assimilation and amino acid metabolism tended to increase under excess NH 4 + -N compared with the control, suggestive of the imbalanced carbon and nitrogen (C-N) metabolisms. In support, activated GS and GOGAT cycle was observed, evidenced by higher activities of GS and GOGAT enzymes. To our knowledge, this work is the first description that excess NH 4 + -N results in chloroplast ultrastructural damages and the first proteomic evidence to support that excess NH 4 + -N can lead to a decline in photosynthesis and imbalance of C-N metabolism in submerged macrophytes., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Soil and water contamination from heavy metals and metalloids is one of the most discussed and caused adverse effects on food safety and marketability, crop growth due to phytotoxicity, and environmental health of soil organisms. A hydroponic investigation was executed to evaluate the influence of citric acid (CA) on copper (Cu) phytoextraction potential of jute ( Corchorus capsularis L.). Three-weeks-old seedlings of C. capsularis were exposed to different Cu concentrations (0, 50, and 100 μM) with or without the application of CA (2 mM) in a nutrient growth medium. The results revealed that exposure of various levels of Cu by 50 and 100 μM significantly ( p < 0.05) reduced plant growth, biomass, chlorophyll contents, gaseous exchange attributes, and damaged ultra-structure of chloroplast in C. capsularis seedlings. Furthermore, Cu toxicity also enhanced the production of malondialdehyde (MDA) which indicated the Cu-induced oxidative damage in the leaves of C. capsularis seedlings. Increasing the level of Cu in the nutrient solution significantly increased Cu uptake by the roots and shoots of C. capsularis seedlings. The application of CA into the nutrient medium significantly alleviated Cu phytotoxicity effects on C. capsularis seedlings as seen by plant growth and biomass, chlorophyll contents, gaseous exchange attributes, and ultra-structure of chloroplast. Moreover, CA supplementation also alleviated Cu-induced oxidative stress by reducing the contents of MDA. In addition, application of CA is helpful in increasing phytoremediation potential of the plant by increasing Cu concentration in the roots and shoots of the plants which is manifested by increasing the values of bioaccumulation (BAF) and translocation factors (TF) also. These observations depicted that application of CA could be a useful approach to assist Cu phytoextraction and stress tolerance against Cu in C. capsularis seedlings grown in Cu contaminated sites.

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/m 2 ·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 CO 2 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.

This study provides a full description of the responses of the crop energy plant Zea mays to stress induced by Cd and Pb, in view of a possible extensive use in phytoattenuation of metal-polluted soils. In this perspective, (i) the uptake capability in root and shoot, (ii) the changes in growth pattern and cytological traits, and (iii) the photosynthetic efficiency based on photochemistry and the level of key proteins were investigated in hydroponic cultures. Both metals were uptaken by maize, with a translocation factor higher for Cd than Pb, but only Cd-treated plants showed a reduced growth compared to control (i.e., a lower leaf number and a reduced plant height), with a biomass loss up to 40%, at the highest concentration of metal (10 -3  M). The observation of cytological traits highlighted ultrastructural damages in the chloroplasts of Cd-treated plants. A decline of Rubisco and D1 was observed in plants under Cd stress, while a relevant increase of the same proteins was found in Pb-treated plants, along with an increase of chlorophyll content. Fluorescent emission measurements indicated that both metals induced an increase of NPQ, but only Cd at the highest concentration determined a significant decline of F v /F m . These results indicate a different response of Z. mays to individual metals, with Pb triggering a compensative response and Cd inducing severe morpho-physiological alterations at all investigated levels. Therefore, Z. mays could be successfully exploited in phytoattenuation of Pb-polluted soil, but only at very low concentrations of Cd to avoid severe plant damages and biomass loss.

The chloroplast being an important organelle of plant cells could possibly be associated with plant cytoplasmic male sterility (CMS). To better understand the correlation between (CMS) and chloroplast, we presented a comprehensive analysis based on the changes of photosynthetic parameters, chloroplasts ultrastructure, soluble sugar and starch content, the relative expression of sugar and starch metabolism genes, and chloroplast genome in rice isonuclear alloplasmic CMS lines at the flowering stage. Leaf gas exchange parameters did not affect by CMS lines (M2BS and M2A), although intercellular CO 2 concentration (C i ) was influenced in both M2BS and M2A. Ultrastructural observation results indicated that many starch granules were observed in the chloroplast of CMS lines, especially bigger size in M2BS, while few ones in M2B. Only the chloroplasts of M2A contained some additional number of lipoids compared with those of the other two lines (M2B and M2BS). Soluble sugar and starch contents in CMS lines (M2BS and M2A) were significantly higher than those in maintainer line (M2B) (p < 0.01). The relative expression of sugar and starch metabolism genes indicated the imbalance of starch and sugar synthesis and decomposition may lead to accumulation of starch granules and demonstrated the presence of cytoplasmic effects. Moreover, chloroplast genome sequencing results showed similarity in both CMS lines, which revealed different single nucleotide polymorphisms (SNPs) and insertion/deletion (InDels) models compared with their maintainer line. Those models were located in psbD, rpoC2, rpl33, psbB, ndhA, ndhH, and intergenic regions. These findings, aligned with the possible association of CMS characteristics with cpDNA and genetically close relationship among both CMS lines, may contribute for future research.

We examined the changes of photosynthetic characteristics and chloroplast ultrastructure in mesophyll cell of summer maize in response to different light intensities in the field, with the summer maize hybrid Denghai 605 as experimental material. Two treatments of both shading (S) and increasing light (L) from flowering to physiological maturity stage were designed, with the ambient sunlight treatment as control (CK). Under shading treatment, poorly developed thylakoid structure, blurry lamellar structure, loose granum, large gap between slices and warping granum were the major characteristics in chloroplast. Meanwhile, photosynthetic rate (P n ), transpiration rate, stomatal conductance, chlorophyll content, and actual photo-chemical efficiency (Φ PSII ) decreased, whereas the maximal photochemical efficiency and non-photochemical quenching increased, which resulted in decreases in grain yield under shading treatment. However, a better development was observed in chloroplasts for L treatment, with the number of grana and lamellae increased and lamellae arranged compactly. In addition, P n and Φ PSII increased under L treatment, which increased grain yield. The chloroplast arrangement dispersed in mesophyll cells and chloroplast ultrastructure was destroyed after shading, and then chlorophyll synthesis per unit leaf area and photosynthetic capacity decreased. In contrast, the number of grana and lamellae increased and lamellae arranged compactly after increasing light, which are beneficial for corn yield.

A great deal of literature is available regarding the environmental and ecological effects of rare earth element pollution on plants. These studies have shown that excess lanthanum (La) (III) in the environment can inhibit plant growth and even cause plant death. Moreover, inhibition of plant photosynthesis is known to be one of the physiological bases of these damages. However, the mechanism responsible for these effects is still unclear. In this study, the mechanism of La(III)-induced damage to plant photosynthesis was clarified from the viewpoint of the chloroplast ultrastructure, the contents of chloroplast mineral elements and chlorophyll, the transcription of chloroplast ATPase subunits and chloroplast Mg(2+)-ATPase activity, in which rice was selected as a study object. Following treatment with low level of La(III), the chloroplast ultrastructure of rice was not changed, and the contents of chloroplast mineral elements (Mg, P, K, Ca, Mn, Fe, Ni, Cu, and Zn) increased, but the chlorophyll content did not change significantly. Moreover, the transcription of chloroplast ATPase subunits, chloroplast Mg(2+)-ATPase activity, the net photosynthetic rate and growth indices increased. Following treatment with high levels of La(III), the chloroplast ultrastructure was damaged, chloroplast mineral elements (except Cu and Zn) and chlorophyll contents decreased, and the transcription of chloroplast ATPase subunits, chloroplast Mg(2+)-ATPase activity, the net photosynthetic rate and growth indices decreased. Based on these results, a possible mechanism of La(III)-induced damage to plant photosynthesis was proposed to provide a reference for scientific evaluation of the potential ecological risk of rare earth elements in the environment., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Pollution of agricultural soils caused by widely employed plastic products, such as phthalic acid esters (PAEs), are becoming widespread in China, and they have become a threat to human health and the environment. However, little information is available on the influence of PAEs on vegetable crops. In this study, effects of different dimethyl phthalate (DMP) treatments (0, 30, 50, 100, and 200 mg L(-1)) on seed germination and growth of cucumber seedlings were investigated. Although germination rate showed no significant difference compared to control, seed germination time was significantly delayed at DMP greater than 50 mg L(-1). Concentrations of DMP greater than 30 mg L(-1) reduced cucumber lateral root length and number. The measurement of five physiological indexes in cucumber leaves with increasing DMP concentration revealed a decrease in leaf chlorophyll content, while proline and H2O2 contents increased. Peroxidase (POD) and catalase (CAT) activities increased in cucumber plants under 30 and 50 mg L(-1) DMP treatments compared to control; while after a 7-day treatment, these activities were seriously reduced under 100 and 200 mg L(-1) DMP treatments. According to transmission electron microscopy (TEM) micrographic images, the control and 30 mg L(-1) DMP treatments caused no change to leaf chloroplast shape with well-structured thylakoid membrane and parallel pattern of lamellae. At concentrations higher than 30 mg L(-1), DMP altered the ultrastructure of chloroplast, damaged membrane structure, disordered the lamellae, and increased the number and volume of starch grains. Moreover, the envelope of starch grains began to degrade under 200 mg L(-1) DMP treatment.

Silicon was shown to alleviate the negative effects of various biotic and abiotic stresses on plant growth. Although the positive role of Si on toxic and heavy metal Cd has been already described, the mechanisms have been explained only partially and still remain unclear. In the present study we investigated the effect of Si on photosynthetic-related processes in maize exposed to two different levels of Cd via measurements of net photosynthetic rate (AN), chlorophyll a fluorescence and pigment analysis, as well as studies of leaf tissue anatomy and cell ultrastructure using bright-field and transmission electron microscopy. We found that Si actively alleviated the toxic syndromes of Cd by increasing AN, effective photochemical quantum yield of photosystem II (ϕPSII) and content of assimilation pigments, although did not decrease the concentration of Cd in leaf tissues. Cadmium did not affect the leaf anatomy and ultrastructure of leaf mesophyll's cell chloroplasts; however, Cd negatively affected thylakoid formation in chloroplasts of bundle sheath cells, and this was alleviated by Si. Improved thylakoid formation in bundle sheath's cell chloroplasts may contribute to Si-induced enhancement of photosynthesis and related increase in biomass production in C4 plant maize., (Copyright © 2015 Elsevier Inc. All rights reserved.)

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]

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]

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.)

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.)

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]

Copyright of Bulletin of Botanical Research is the property of Bulletin of Botanical Research 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.)

Chloroplast ultrastructural changes were investigated in chilling-sensitive (cucumber, Cucumis sativus L.) and cold-tolerant (winter rye, Secale cereale L.) plants during low-temperature hardening. Cold hardening was found to shorten the total length of thylakoid membranes in chloroplasts of both species by 20–30%. The reduction in total membrane length in cucumber was due to the decline in membrane length of both grana and stroma thylakoids, whereas the membrane length of grana thylakoids in winter rye was reduced without changes in length of stroma thylakoid membranes. In cucumber plants, the chloroplast section area decreased during hardening in parallel with more than threefold increase in starch grain area. In winter rye, the chloroplast area increased after hardening, while starch grains were completely absent. Both S. cereale and C. sativus retained photosynthetic activity at hardening temperatures, although photosynthetic rates decreased by 2–3 times compared to those in untreated plants. The content of soluble sugars in leaves increased by 20% in cucumber and increased more than threefold in winter rye. The accumulation of starch in cucumber chloroplasts provides evidence that a significant part of photosynthetic products was removed from the osmotic pool, which limited the efficiency of hardening in C. sativus plants. In winter rye plants, the thylakoid system rearrangement and the lack of starch synthesis in chloroplasts caused a severalfold increase in the content of intracellular soluble sugars, which ensured highly efficient low-temperature hardening of these plants. [ABSTRACT FROM AUTHOR]

The effect of cadmium (Cd) on the ultrastructure of plastid apparatus in leaves of Elodea nuttallii (Planch). H. St. John was investigated in experimental conditions using transmission electron microscopy (TEM). The experimental plants were cultivated in a green house environment after preliminary adaptation. The plants were exposed to Cd during 5 days period with concentrations 1 mg/l and 3 mg/l, consistent with previous studies. Cultivated plants under condition of the experiment without Cd were used as the controls. The results showed that at concentration 1 mg/l Cd chloroplasts have a well organized internal membrane system relative to the control, but fragmentation and weak swollen thylakoids were observed. Increasing of cadmium concentration at 3 mg/l Cd show hardly affected plastid ultrastructure, as swollen thylakoid membrane and reduction of grana stacks. The established structural changes of photosynthetic apparatus of E. nuttallii are analyzed and compared to previous researches of cadmium toxicity on E. canadensis under the same conditions. [ABSTRACT FROM AUTHOR]

This review presents a comparative analysis of the literature and the authors' data on the ultrastructural reorganization of plant chloroplasts adapting to abiotic factors of different nature—low temperature (factor of a physical nature) and chloride salinity (factor of a chemical nature). All ultrastructural changes in chloroplasts are considered in close relationship to the physiological, biochemical, and functional adaptive changes of the photosynthetic apparatus (PSA). The review discusses the adaptive value and emphasizes the nonspecific nature of ultrastructural transformations occurring in plant chloroplasts under abiotic stress. A separate section considers the effect of metal nanoparticles on the PSA and the nanoparticle-aided modeling of the PSA responses to stresses. [ABSTRACT FROM AUTHOR]

BACKGROUND In some cultivars, yellowing resulting from chlorophyll breakdown has a direct and negative effect on food supply and health. The 'Zaosu' pear (Pyrus bretschneideri Rehd.), a commercial Asian pear cultivar in China, rapidly turns yellow when stored at room temperature after harvest. To develop techniques that delay or suppress chlorophyll degradation, the effects of methyl salicylate (MeSA) on yellowing in 'Zaosu' pear fruit during storage were evaluated. RESULTS: Compared with the untreated fruit, the application of 0.05 mmol L−1 MeSA delayed the decline of the total chlorophyll, chlorophyll a and chlorophyll b content, and maintained more intact chloroplasts with fewer and smaller plastoglobuli. Methyl salicylate suppressed enzyme activities, including chlorophyllase, chlorophyll‐degrading peroxidase, Mg dechelatase, and pheophytinase, and the expression levels of NYC, NOL, CLH, SGR, PPH, PAO and RCCR in treated fruit. CONCLUSION: Methyl salicylate could delay chlorophyll breakdown in the fruit. The results also suggested that the conversion from chlorophyll a to pheophorbide a could proceed via two pathways, and that alternative pathways for the breakdown of chlorophyll a exist in 'Zaosu' pears. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract Atrazine is an ingredient in photosynthesis-inhibiting herbicides and has been widely used to combat weeds in farmland. However, most atrazine that is applied fails to degrade in the soil and subsequently affects non-target plants. In this study, we investigated the influence of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae on the photosynthesis-related parameters, chlorophyll content, and chloroplast ultrastructure in alfalfa plants, some of which had been exposed to atrazine. Our results showed that the percentage of AMF hyphal colonization reached 91.23% 35 days after the alfalfa was planted, which suggests a symbiotic relationship between F. mosseae and alfalfa roots. F. mosseae alleviated the inhibition of net photosynthesis and stomatal function significantly in alfalfa exposed to atrazine for 24 h. A chlorophyll fluorescence analysis revealed that F. mosseae prevented a major reduction in the performance of photosystem II (PSII) photochemistry in the presence of atrazine, such as the relative decrease of F v /F m between the non-mycorrhizal and F. mosseae mycorrhizal treatments was 4.4% and 5.8% after 24 and 48 h of atrazine exposure time. However, F. mosseae has no significant alleviation on a sharp reduction in the chlorophyll a, chlorophyll b and carotenoid content in alfalfa exposed to atrazine. For the chloroplast ultrastructure in alfalfa exposed to atrazine, the number of both plastoglobules and partial granal stacks was greater in the presence of F. mosseae. In general, our results indicate that the F. mosseae inoculation was beneficial to sustain photosynthesis-related performance, such as net photosynthesis, stomatal conductance, the maximum quantum yield (F v /F m) and effective quantum yield (Φ PSII) of PSII photochemistry in alfalfa after exposure to atrazine, because the mycorrhizal alfalfa had a greater number of plastoglobules and granal stacks in the chloroplast, thereby enhancing its resistance to the oxidative damage induced by atrazine. Highlights • AMF mitigated the inhibition of photosynthesis-related parameters by atrazine. • AMF has no alleviation on a sharp reduction in chlorophyll content by atrazine. • The number of plastoglobules and granal stacks was greater in the presence of AMF. [ABSTRACT FROM AUTHOR]

Foliar uptake of gaseous NO2 mainly occurs through the stomata and disrupts normal plant growth, but no detailed reports about the physiological responses of plants exposed to NO2 are available. In this study, to study leaf physicochemical responses, stomatal characteristics and chloroplast structure, we observed the leaves of Carpinus putoensis W.C.Cheng after exposure to NO2 (6 µL/L) for five time periods (0, 1, 6, 24, and 72 h) and after 30 days of recovery following NO2 exposure. Our results showed that short-duration exposure to a high concentration of NO2 had significant negative impacts (p < 0.05) on the chlorophyll content, photosynthesis and chloroplast-related physicochemical processes of C. putoensis leaves; with the exception of one hour of NO2 exposure, which was helpful for plant physiological responses. Moreover, NO2 exposure significantly increased the thickness of the palisade/spongy tissue and caused swelling of the thylakoids within the chloroplasts; this thylakoid swelling could be reversed by removing the pollutant from the air flow. Restoration of unpolluted air alleviated the toxic effects of NO2, as indicated by an increased chlorophyll content, net photosynthesis, and PSII maximum quantum yield. These results could support the development of a treatment for roadside trees that are exposed to NO2 as a major road pollutant. [ABSTRACT FROM AUTHOR]

Maize (Zea mays L.) is the important crop over the world. Nitrogen (N) as necessary element affects photosynthetic characteristics and grain yield of summer maize. In this study, N0 (0 kg N ha-1), N1 (129 kg N ha-1), N2 (185 kg N ha-1), and N3 (300 kg N ha-1) was conducted using hybrid 'ZhengDan958' at Dawenkou research field (36°11'N, 117°06'E, 178 m altitude) in the North China Plain to explore the effects of N rate on photosynthetic characteristics and chloroplast ultrastructure. Gas exchange parameters, chlorophyll fluorescence parameters, leaf area index (LAI), chlorophyll SPAD value, chloroplast ultrastructure, dry matter weight and grain yield were measured. At physiological maturity stage, dry matter weight and grain yield of N2 increased by 33-52% (P ≤ 0.05) and 6-32% (P ≤ 0.05), respectively, compared with other treatments. During the growing from silking (R1) to milk (R3) stage, LAI of N0 and N1 were 35-38% (P ≤ 0.05) and 9-23% (P ≤ 0.05) less than that of N2, respectively. Chlorophyll SPAD value of N0 and N1 were 13-22% (P ≤ 0.05) and 5-11% (P ≤ 0.05) lower than that of N2. There was no significant difference in LAI and chlorophyll SPAD value between N2 and N3 during the period from R1 to R3 (P > 0.05). The net photosynthetic rate (Pn), maximal quantum efficiency of PSII (Fv/Fm) and quantum efficiency of PSII (ΦPSII) were higher with the increase of N rate up to N2 (P ≤ 0.05), and those of N3 were significantly less than N2 (P ≤ 0.05). In compared with N2, the chloroplast configuration of N0 and N1 became elliptical, almost circular or irregular. The membrane of chloroplast and thylakoid resolved with growing stage, and the number of chloroplast per cell and lamellae per grana decreased under N0 and N1 treatment (P ≤ 0.05). Under N0 and N1 treatments, summer maize had more negative photosynthetic characteristics. The more number of osmium granule and vesicle and the larger gap between lamellae were shown in N3. Therefore, N2 treatment, 185 kg N ha-1, is the appropriate application rate for grain yield, photosynthesis and chloroplast ultrastructure. [ABSTRACT FROM AUTHOR]

Marchantia polymorpha is a convenient model for studying light of different spectral compositions on various physiological and biochemical processes because its photoreceptor system is vastly simplified. The influence of red light (RL, 660 nm), far-red light (FRL, 730 nm), blue light (BL, 450 nm), and green light (GL, 525 nm) compared to white light (high-pressure sodium light (HPSL), white LEDs (WL 450 + 580 nm) and white fluorescent light (WFL) on photosynthetic and transpiration rates, photosystem II (PSII) activity, photomorphogenesis, and the expression of light and hormonal signaling genes was studied. The ultrastructure of the chloroplasts in different tissues of the gametophyte M. polymorpha was examined. FRL led to the formation of agranal chloroplasts (in the epidermis and the chlorenchyma) with a high starch content (in the parenchyma), which led to a reduced intensity of photosynthesis. BL increased the transcription of genes for the biosynthesis of secondary metabolites - chalcone synthase (CHS) , cellulose synthase (CELL) , and L-ascorbate peroxidase (APOX3) , which is consistent with the increased activity of low-molecular weight antioxidants. FRL increased the expression of phytochrome apoprotein (PHY) and cytokinin oxidase (CYTox) genes, but the expression of the phytochrome interacting factor (PIF) gene decreased, which was accompanied by a significant change in gametophyte morphology. Analysis of crosstalk gene expression, and changes in morphology and photosynthetic activity was carried out. • The MpPHY is very sensitive to the presence of RL in the FRL spectrum. • Transcription of MpPIF is not inhibited by FRL. • FRL causes the formation of agranal chloroplasts and starch accumulation. • The BL causes the formation of an asymmetrical thallus and an increase in gene transcription. [ABSTRACT FROM AUTHOR]

The effects of cadmium and lead were investigated in Cynara cardunculus L. Plant uptake by root and shoot, changes in cell ultrastructure and photosynthetic efficiency, photosynthetic key protein levels, as well as regulation of stress-induced Hsp70 were examined. Cynara cardunculus accumulated Cd and Pb in their tissue, with a different trend for the two metals. The prompt translocation of Cd to the shoot may justify the ultrastructural injuries, especially observed in chloroplasts. However, Cd- treated plants did not show any decline in photochemistry; it is likely that Cd in shoot tissue triggers defense mechanisms, increasing the level of proteins involved in photosynthesis (i.e., Rubisco and D1 increased 7 and 4.5 fold respectively) as a compensatory response to neutralize chloroplast damage. The accumulation of Pb mainly in root, can explain the increase in Hsp70 level (23 folds) in this tissue. Pb reached the shoots, even at low amounts, causing an overall significant change in some photochemical parameters (QY and NPQ decreases and increases of 25%, respectively). The results suggest a higher sensitivity of C. cardunculus to Pb than Cd, although maximal photochemical efficiency suggests that this species seems to tolerate Pb and Cd and hence, it is a suitable candidate for phytoremediation. [ABSTRACT FROM AUTHOR]

The objective of the present study was to evaluate the effects of different light emitting diodes (LEDs) on growth, photosynthetic characteristic and chloroplast ultrastructure of upland cotton (Gossypium hirsutum L.) seedlings. Seedlings of the cultivar Sumian 22 were grown under seven different lights including blue (B) plus red (R) LEDs BR (1:8, 1:3, 1:1, 3:1), B LEDs, R LEDs and fluorescent lamps (FL) with the 100 μ mol m-2 s-1 photosynthesis photon flux (PPF) and a 12 hour photoperiod for 40 days. Compared with FL, fresh mass, dry mass, root length, stem width, root activity, length of palisade tissue and stomatal frequencies were significantly greater as well as the thickest grana lamella in chloroplast in seedlings grown under BR1:8 LEDs; The chlorophyll a, chlorophyll b, total chlorophyll contents, photosynthetic rate, leaf thickness, spongy tissue length and stomatal areas were highest in seedlings under B LEDs; The stem length, leaf area, sucrose, soluble sugar and starch concentrations were highest as well as the greatest number and volume of starch grains in chloroplast in seedlings under R LEDs. It was suggested that BR1:8 LEDs might be used as a primary light for the cultivation of upland cotton seedlings under controlled conditions. [ABSTRACT FROM AUTHOR]

Portulacaceae is a family that has considerable diversity in photosynthetic phenotypes. It is one of 19 families of terrestrial plants where species having C4 photosynthesis have been found. Most species in Portulaca are in the alternateleaved (AL) lineage, which includes one clade (Cryptopetala) with taxa lacking C4 photosynthesis and three clades having C4 species (Oleracea, Umbraticola and Pilosa). All three species in the Cryptopetala clade lack Kranz anatomy, the leaves have C3-like carbon isotope composition and they have low levels of C4 cycle enzymes. Anatomical, biochemical and physiological analyses show they are all C3-C4 intermediates. They have intermediate CO2 compensation points, enrichment of organelles in the centripetal position in bundle sheath (BS) cells, with selective localization of glycine decarboxylase in BS mitochondria. In the three C4 clades there are differences in Kranz anatomy types and form of malic enzyme (ME) reported to function in C4 (NAD-ME versus NADP-ME): Oleracea (Atriplicoid, NAD-ME), Umbraticola (Atriplicoid, NADP-ME) and Pilosa (Pilosoid, NADP-ME). Structural and biochemical analyses were performed on Pilosa clade representatives having Pilosoid-type leaf anatomy with Kranz tissue enclosing individual peripheral vascular bundles and water storage in the center of the leaf. In this clade, all species except P. elatior are NADP-ME-type C4 species with grana-deficient BS chloroplasts and grana-enriched M chloroplasts. Surprisingly, P. elatior has BS chloroplasts enriched in grana and NAD-ME-type photosynthesis. The results suggest photosynthetic phenotypes were probably derived from an ancestor with NADP-ME-type C4, with two independent switches to NAD-ME type. [ABSTRACT FROM AUTHOR]

Changes of ultrastructural organization of tobacco ( Nicotiana tabacum L. cv. Samsun) chloroplasts associated with plant protection from oxidative stress during hypothermia were studied. It was found that the chilling hardening (6 days at 8°C) was accompanied by the significant reduction in the number of grana in a chloroplast simultaneously with area reduction of a granum that led to 30% decrease in the total area of grana in tobacco chloroplasts. In the course of tobacco plant hardening, approximately twofold decrease in generation rate of superoxide anion radical and 30% decrease in content of hydrogen peroxide occurred, which indicates retardation of oxidative processes in plant cells during the cold exposure. It is suggested that the ultrastructural changes in chloroplast organization that were found may prevent an overreduction of an electron-transport chain under hypothermia, when the ability of the Calvin cycle to utilize ATP and NADP·H is significantly reduced. The balanced work of components of light and dark photosynthetic phases may prevent the excessive generation of reactive oxygen species and render formation of tobacco plant tolerance to hypothermia. [ABSTRACT FROM AUTHOR]

Oxidative stress, antioxidants, fruit yield, tomato (Solanum lycopersicum L.), gamma-aminobutyric acid, chilling stress, chloroplast ultrastructure Erratum: Protective Effect of -Aminobutyric Acid Against Chilling Stress During Reproductive Stage in Tomato Plants Through Modulation of Sugar Metabolism, Chloroplast Integrity, and Antioxidative Defense Systems Keywords: tomato (Solanum lycopersicum L.); gamma-aminobutyric acid; chilling stress; chloroplast ultrastructure; oxidative stress; antioxidants; fruit yield EN tomato (Solanum lycopersicum L.) gamma-aminobutyric acid chilling stress chloroplast ultrastructure oxidative stress antioxidants fruit yield 1 1 2 11/24/21 20211119 NES 211119 Owing to a production error, the author Nihal El Nahhas was not included in the original article when published. [Extracted from the article]

Hydrogen sulphide (H2S) is emerging as a potential molecule involved in physiological regulation in plants. However, whether H2S regulates iron-shortage responses in plants is largely unknown. Here, the role of H2S in modulating iron availability in maize (Zea mays L. cv Canner) seedlings grown in iron-deficient culture solution is reported. The main results are as follows: Firstly, NaHS, a donor of H2S, completely prevented leaf interveinal chlorosis in maize seedlings grown in iron-deficient culture solution. Secondly, electron micrographs of mesophyll cells from iron-deficient maize seedlings revealed plastids with few photosynthetic lamellae and rudimentary grana. On the contrary, mesophyll chloroplasts appeared completely developed in H2S-treated maize seedlings. Thirdly, H2S treatment increased iron accumulation in maize seedlings by changing the expression levels of iron homeostasis- and sulphur metabolism-related genes. Fourthly, phytosiderophore (PS) accumulation and secretion were enhanced by H2S treatment in seedlings grown in iron-deficient solution. Indeed, the gene expression of ferric-phytosiderophore transporter (ZmYS1) was specifically induced by iron deficiency in maize leaves and roots, whereas their abundance was decreased by NaHS treatment. Lastly, H2S significantly enhanced photosynthesis through promoting the protein expression of ribulose-1,5-bisphosphate carboxylase large subunit (RuBISCO LSU) and phosphoenolpyruvate carboxylase (PEPC) and the expression of genes encoding RuBISCO large subunit (RBCL), small subunit (RBCS), D1 protein (psbA), and PEPC in maize seedlings grown in iron-deficient solution. These results indicate that H2S is closely related to iron uptake, transport, and accumulation, and consequently increases chlorophyll biosynthesis, chloroplast development, and photosynthesis in plants. [ABSTRACT FROM AUTHOR]

Limoniastrum guyonianum is an evergreen perennial halophyte. Its response to severe salinity was investigated by exposing ninety-day-old plantlets to a 0–1000 mM NaCl range for 3 months. Growth, water status, electrolyte leakage (EL), malondialdehyde (MDA) content, salt excretion, leaf pigment content, photosynthetic parameters, chloroplast ultrastructure, and contents of Na + , Cl − , K + , Ca 2+ , Mg 2+ , proline and polyphenols were determined. Results of these studies indicate that L. guyonianum is a facultative halophyte and can survive at 1000 mM NaCl. Plants treated with 300 mM NaCl had a 25% increase in whole plant fresh mass that is attributed to increased photosynthetic activity and adequate water uptake. Sodium and chloride accumulation increased with salinity and was associated with significant reductions in leaf K + , Ca 2+ and Mg 2+ concentrations due to excretion out of leaves. Consequently, photosynthetic machinery was highly preserved against toxic ions. Polyphenol accumulation increased with salt treatments while lipid peroxidation decreased with salinity levels at 200–1000 mM NaCl. Proline accumulation increased with salt treatments up to and including 400 mM NaCl. The increase in intrinsic water use efficiency at medium salt levels indicates that L. guyonianum is efficient at using the low available water under salt stress. These physiological and biochemical responses to salinity and the salt excretion process allowed L. guyonianum to tolerate severe salinity. [ABSTRACT FROM AUTHOR]

In the field, apple trees ( Malus domestica L.) do not exhibit visible deficient symptoms when affected by hidden zinc (Zn) deficiency, while internal injury in the leaves may prior occurred. We named the leaves on Zn deficient trees without and with visible rosette symptoms as ‘hidden rosette leaves’ and ‘rosette leaves’, respectively. The healthy leaves of normal trees were named ‘normal leaves’ and selected as the control. The changes in leaf photosynthesis, physiology and internal structure were analyzed to elucidate the damage mechanism of Zn deficiency in apple leaves. We found that the reduction in photosynthesis under Zn deficiency was primarily due to non-stomatal limitation, in particular the changes in photosystem II (PS II). Zinc deficiency significantly reduced chlorophyll content in the hidden rosette leaves without obvious changes to chloroplasts and grana number. The intrinsic efficiency of PS II ( F v ′/ F m ′), actual photochemical efficiency of PS II ( ϕ PS II) and electron transport rate (ETR) were all significantly decreased in both hidden rosette leaves and rosette leaves, while a further significant increase in the minimal fluorescence ( F o ) along with reductions in maximum photochemical efficiency of PSII ( F v / F m ) and photochemical quenching (qP) occurred in rosette leaves. These results indicate that the decrease in chlorophyll content and inhibition of PS II light-harvesting activity may account for the photosynthesis reduction during the initial stage of Zn deficiency. As Zn deficiency aggravated, cellular deficient characteristics like abnormal cell arrangements and disorganization of thylakoids became more exaggerated; visible external symptoms of Zn deficiency appeared with internal alterations, including photosynthetic apparatus damage accompanied by subsequent chloroplast and grana disintegration. We concluded that the PS II activity was relatively sensitive to Zn deficiency, hence the chlorophyll fluorescence parameters like F v ′/ F m ′ and ϕ PS II may be used as predictive indictors for hidden Zn deficiency on apple trees. [ABSTRACT FROM AUTHOR]

The present work examined seven Hypericum species ( H. perforatum, H. humifusum, H. kalmianum, H. annulatum, H. tomentosum, H. pulchrum, and H. rumeliacum) produced in vitro and regenerated after cryopreservation. The aim of the study was to assess, by means of light microscopy (LM) and transmission electron microscopy (TEM), the effect of freezing temperature on leaf histological organization and mesophyll chloroplast ultrastructure. Histological analysis showed a negative effect of ultralow temperatures on leaf tissue structure in H. pulchrum and a positive effect in H. perforatum. The TEM analysis showed that chloroplasts from ultralow temperature treated H. annulatum, H. tomentosum, and H. rumeliacum had a typically structured internal membrane system without destruction of thylakoid membranes, however, those of H. humifusum had very high grana, and in H. perforatum, chloroplast thylakoid destruction occurred. The chloroplast internal membrane system of in vitro cultured control plants and in vitro cultured cryopreserved plants of H. kalmianum and H. pulchrum had a specific spatial orientation without any destruction of the membranes. The results show a specific response of each species to these experimental conditions. [ABSTRACT FROM AUTHOR]

The effect of exogenous CaCl on photosynthesis, antioxidant system, and chloroplast ultrastructure of tomato leaves under low night temperature (LNT) was investigated. Tomato seedlings were pretreated with 27 mM CaCl, 5 mM EGTA, respectively, for 4 days and then exposed to LNT treatment at 6 °C for 7 days. Plants treated with CaCl showed higher photosynthesis, increased stomatal aperture and chloroplast area, and decreased number of starch grains under LNT stress than those treated with distilled water. LNT increased the contents of superoxide radicals, hydrogen peroxide, and malondialdehyde, whereas calcium application reduced the contents of these compounds. The increase in antioxidant activities caused by LNT stress was also enhanced by the application of exogenous calcium. The opposite effects were observed with ethylene glycol-bis-(2-aminoethyl) tetraacetic acid pretreatment. CaCl application improved photosynthesis in LNT-stressed plants. Such improvement was associated with increased stomatal conductance, improved antioxidant activities, and adjusted chloroplast structure. These results suggest that CaCl application improved photosynthesis in LNT-stressed plants. It provided fundamental information for further molecular mechanism research. [ABSTRACT FROM AUTHOR]

The chloroplast protein AtDeg5 is a serine-type protease peripherally attached to thylakoid membrane at its lumenal side. Since reliable data regarding the role of AtDeg5 in controlling the course of growth and developmental processes are extremely limited, two independent T-DNA insertional lines with different extent of AtDeg5 reduction were prepared and ontogenesis stage-based analysis performed. Both mutant lines displayed a compensatory overaccumulation of AtDeg8. The repression of AtDeg5 protease altered a range of phenotypic features in at least one of the mutants, with the most prominent being changes in chronological progression of development and growth of individual rosette leaves, flower production and silique ripening as well as in the area of fully expanded leaves and chloroplast ultrastructure. By analyzing the results of parallel-mutant screening we conclude that AtDeg8 overdose may rescue 23% of AtDeg5 deficiency with regard to some AtDeg5-controlled traits; alternatively AtDeg5 may have catalytic sites in excess so that these traits might remain unaltered when AtDeg5 pool is reduced by 23%. For some other AtDeg5-dependent traits the absence of excessive amount of AtDeg5 catalytic sites, lack of AtDeg5 dosage effect and inability of AtDeg8 to compensate deficiency or absence of AtDeg5 occurred. [ABSTRACT FROM AUTHOR]

Cabomba Aublet is useful as a genetic model of angiosperm evolution. Previous anatomical studies and preliminary light microscopic observations on C . caroliniana A Gray revealed the presence of dimorphic chloroplasts in both types of leaves, floating and submerged leaves. Leaf anatomy and chloroplasts ultrastructure were analyzed and compared. The chloroplast ultrastructure of the mesophyll and epidermal cells is different. Mesophyll chloroplasts have several plastoglobuli, large starch grains and grana formed by an average of 29 thylakoids. Epidermal chloroplasts are smaller, have grana formed by an average of 9 thylakoids and starch grains are occasional and smaller. A statistical analysis ( t -test) was made to determine if differences between chloroplasts are significant. The ultrastructure of the epidermis chloroplast is similar to the one of sun leaves chloroplasts and the ultrastructure of the mesophyll chloroplast is similar to the one of shade chloroplast observed in other species. [ABSTRACT FROM AUTHOR]

Seasonal variations of chloroplast thylakoids and plasma membrane ultrastructure and changes in some biochemical parameters (e.g., metal accumulation, photosynthetic pigments, carbohydrates, lipid peroxidation, and electrolyte leakage) were studied in fronds of Salvinia minima plants exposed to increasing concentrations of Cr(VI) in both winter and summer. Disorganization of stacked (grana) and unstacked (stroma lamellae) thylakoids was greater in winter chloroplasts than in summer chloroplasts. Plasma membrane was less affected than thylakoids. Photosynthetic pigments, lipid peroxidation, soluble sugars, and starch were affected differently in winter and summer. Our results suggest that much greater ultrastructural alterations and changes in metabolite levels occurring in winter fronds are produced by higher oxidative stress resulting from the interactive effect between low temperature, low solar irradiance, and Cr(VI) toxicity, rather than from metal accumulation per se. Seasonal differences occurring in chloroplast ultrastructure and metabolite concentrations were discussed in relation to metabolic implications. Evaluated parameters represent a relevant approach to enhance knowledge on performance and fitness of plants exposed to heavy metals under fluctuating environmental conditions. This work also indicates that selection of suitable macrophytes to remove Cr(VI) requires an additional analyzing focus on structural and metabolic interactions that occur in plants exposed to heavy metals in contrasting seasons. [ABSTRACT FROM AUTHOR]

When following low-temperature acclimation (5 days at 2°C) of cold-resistant plants of Arabidopsis ( Arabidopsis thaliana Heynh. (L.), ecotype Columbia) in relation to the changes in chloroplast ultrastructure, we registered the high efficiency of hardening and the ability of hardened plants to lower a threshold of frost damage by about 3°C. During hardening, the area of grana in the chloroplasts more than doubled, with considerably increased numbers of thylakoids per granum and thylakoids per chloroplast. The rate of apparent photosynthesis decreased to lesser extent than the rate of dark respiration, as a result the content of soluble sugars increased fourfold, ensuring an adaptive reorganization of metabolism, which enabled the hardened plants to survive even at below-zero temperatures (up to −7°C). The authors conclude that a considerable increase in the number of thylakoids in the chloroplasts helps maintain photosynthesis at low above-zero temperatures and is a prerequisite for the accumulation of soluble sugars in Arabidopsis leaves. [ABSTRACT FROM AUTHOR]

Humic acid (HA) is natural biological organic fertilizer derived from organic waste materials, which shows a highly promoting effect on plant growth and development. However, the mechanisms responsible for the promoting effect of humic acid on the growth and development are poorly understood. In this study, the physiological mechanisms of foliar humic acid (FHA) fertilizer on chrysanthemum growth and development from the viewpoint of photosynthesis and chloroplast ultrastructure were investigated. Seedlings of chrysanthemum were sprayed with the same volume of distilled H 2 O (control), inorganic NPK fertilizer and organic foliar humic acid fertilizer every 15 days (15, 30, 45, 60 days after transplanting). The results showed that the morphological indices (stem diameter, fresh weights of shoots and roots, the root to shoot ratios, dry weights of shoots and roots, leaf area, flower diameter), the net photosynthesis rate, the chlorophyll fluorescence, the content of chlorophyll and the chloroplast ultrastructure of chrysanthemum improved obviously after foliar application of humic acid compared with those of the control and the NPK fertilizer. The promoting effect of the humic acid fertilizer showed an obvious dose-effect. The results from correlation analysis indicated that the responses of the foliar humic acid fertilizer on growth and development of chrysanthemum could be related with a constitutive increased net photosynthetic rate due to the high content of chlorophyll and the improved chloroplast ultrastructure. [ABSTRACT FROM AUTHOR]

We analyzed the desert moss Bryum argenteum Hedw., a dominant moss in biological soil crusts in northwestern China, during dehydration and rehydration. There was almost no change in chlorophyll content between hydrated and almost completely desiccated B. argenteum samples. The amounts of thylakoid protein complexes, including the PSI monomer, PSII supercomplex, the PSII monomer, and LHCII, gradually decreased as the dehydration time of B. argenteum was extended. Analysis by two-dimensional sodium dodecylsulfate-urea-polyacrylamide gel electrophoresis showed that the amount of the PSII core subunits CP47 and CP43 and the PSI core subunits PsaA/B decreased during dehydration. The amount of thylakoid protein complexes increased rapidly during rehydration under light conditions, but increased slowly, and to lower levels, during rehydration in the dark. Rehydration of B. argenteum in chloramphenicol solution under light conditions resulted in a decrease in FV/ FM within 10 min. An analysis of chloroplast ultrastructure showed that the number of grana decreased during dehydration. Taken together, our results suggest that the thylakoid protein complexes of B. argenteum degrade during dehydration and then reassemble during rehydration, and that this affects the full recovery of photosynthesis in this species. [ABSTRACT FROM AUTHOR]

Heavy-metal toxicity in soil is one of the major constraints for oilseed rape ( Brassica napus L.) production. One of the best ways to overcome this constraint is the use of growth regulators to induce plant tolerance. Response to cadmium (Cd) toxicity in combination with a growth regulator, 5-aminolevulinic acid (ALA), was investigated in oilseed rape grown hydroponically in greenhouse conditions under three levels of Cd (0, 100, and 500 μM) and three levels of foliar application of ALA (0, 12.5, and 25 mg l). Cd decreased plant growth and the chlorophyll concentration in leaves. Foliar application of ALA improved plant growth and increased the chlorophyll concentration in the leaves of Cd-stressed plants. Significant reductions in photosynthetic parameters were observed by the addition of Cd alone. Application of ALA improved the net photosynthetic and gas exchange capacity of plants under Cd stress. ALA also reduced the Cd content in shoots and roots, which was elevated by high concentrations of Cd. The microscopic studies of leaf mesophyll cells under different Cd and ALA concentrations showed that foliar application of ALA significantly ameliorated the Cd effect and improved the structure of leaf mesophyll cells. However, the higher Cd concentration (500 μM) could totally damage leaf structure, and at this level the nucleus and intercellular spaces were not established as well; the cell membrane and cell wall were fused to each other. Chloroplasts were totally damaged and contained starch grains. However, foliar application of ALA improved cell structure under Cd stress and the visible cell structure had a nucleus, cell wall, and cell membrane. These results suggest that under 15-day Cd-induced stress, application of ALA helped improve plant growth, chlorophyll content, photosynthetic gas exchange capacity, and ultrastructural changes in leaf mesophyll cells of the rape plant. [ABSTRACT FROM AUTHOR]

In different plant species, vanadium has been considered either as beneficial or as a toxic element, or even as secondary metabolism elicitor, but the mechanisms involved are still not completely understood. In this study, the responses of Phaseolus vulgaris L. cv. Contender roots and leaves to different vanadyl sulfate concentrations were studied. The plants grown hydroponically with V had thicker roots, a less developed main root, and a smaller number of secondary roots than the control plants. The V content in roots and leaves was correlated with V supply concentration but the V content in leaf was always much lower than in the root, which leads us to conclusion that V accumulates in the roots and only small quantities are transferred to the leaves. However, thylakoid disorganisation was observed in the chloroplasts of plants grown with vanadyl sulphate. [ABSTRACT FROM AUTHOR]

Abstract: This study investigated the effects of ethylene in storage and 1-methylcyclopropene (1-MCP) pretreatment on post-storage leaf senescence as measured by changes in photosynthesis and chloroplast degradation of two Aglaonema cultivars. Potted plants of ‘Chalit''s Fantasy’ and ‘White Tip’ with or without 1-MCP treatment (600nLL−1 1-MCP for 6h) were exposed to 3.0μLL−1 ethylene, while being stored for 5d at 16°C in the dark, and then placed under an indoor environment for further observation. Plants that did not receive 1-MCP and ethylene served as controls. Ethylene did not affect the stomatal conductance in either cultivar. Ethylene reduced the net CO2 assimilation rate and F v/F m (potential photochemical efficiency of photosystem II) in ‘White Tip’, but not in ‘Chalit''s Fantasy’. Chloroplast number in a palisade or spongy mesophyll cell did not differ among treatments in ‘Chalit''s Fantasy’. However, ethylene-treated ‘White Tip’ had fewer chloroplasts in the mesophyll cells, had more and larger plastoglobules in the chloroplasts, and had looser granal stacking with enlarged thylakoid lumens. ‘Chalit''s Fantasy’ plants that were treated with 1-MCP before exposure to ethylene had higher net CO2 assimilation rates and stomatal conductance than the control or plants that were exposed to ethylene without 1-MCP pretreatment. 1-MCP pretreatment mitigated the injurious effect of ethylene on ‘White Tip’ by increasing net CO2 assimilation rate and F v/F m, and maintaining the quantity and structural integrity of chloroplasts. [Copyright &y& Elsevier]

Abstract: The effects of exogenous spermine (Spm) on plant growth, chlorophyll fluorescence, ultrastructure and anti-oxidative metabolism of chloroplasts were investigated in Cucumis sativus L. under NaCl stress. Salt stress significantly reduced plant growth, chlorophylls content and F v/F m. These changes could be alleviated by foliar spraying with Spm. Salt stress caused an increase in malondialdehyde (MDA) content and superoxide anion generation rate in chloroplasts. Application of Spm significantly increased activities of superoxidase dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7), and ascorbate peroxidase (APX, EC 1.11.1.11) which decreased the levels of and MDA in the salt-stressed chloroplasts. Salt stress decreased the activities of dehydroascorbate reductase (DHAR, EC 1.8.5.1) and glutathione reductase (GR, EC 1.6.4.2) in the chloroplasts and reduced the contents of dehydroascorbate (DAsA) and glutathione (GSH), but increased monodehydroascorbate reductase (MDAR, EC 1.6.5.4) activity. On the other hand, Spm significantly increased the activities of antioxidant enzymes and levels of antioxidants in the salt-stressed chloroplasts. Further analysis of the ultrastructure of chloroplasts indicated that salinity induced destruction of the chloroplast envelope and increased the number of plastoglobuli with aberrations in thylakoid membranes. However, Spm application to salt-stressed plant leaves counteracted the adverse effects of salinity on the structure of the photosynthetic apparatus. These results suggest that Spm alleviates salt-induced oxidative stress through regulating antioxidant systems in chloroplasts of cucumber seedlings, which is associated with an improvement of the photochemical efficiency of PSII. [Copyright &y& Elsevier]

The leaf structure and chloroplast ultrastructure of kidney tea ( Orthosiphon stamineus Benth.) was studied in in vitro culture on standard MS medium supplemented with or without plant growth regulators (PGRs). The cytokinin N-benzyladenine (BA) negatively affected the structure of the palisade parenchyma and chloroplast ultrastructure and increased the stomatal frequency of the adaxial epidermis. The auxin indole-3-butyric acid (IBA) did not modify the morphology of regenerated leaf tissues as well as the chloroplast ultrastructure. The effect of both PGRs applied in combination was manifested in well-differentiated mesophyll parenchyma, typical chloroplast ultrastructure and increased stomatal frequency on both leaf surfaces. This protocol can be suggested for further ex vitro propagation. [ABSTRACT FROM AUTHOR]

The present study was undertaken to investigate the effect of Glomus mosseae on chlorophyll (Chl) content, Chl fluorescence parameters and chloroplast ultrastructure of beach plum seedlings under 2% NaCl stress. The results showed that compared to control, both Chl a and Chl b contents of NaCl + G. mosseae treatment were significantly lower during the salt stress, while Chl a/b ratio increased significantly. The increase of minimal fluorescence of darkadapted state (F), and the decrease of maximal fluorescence of dark-adapted state (F) and variable fluorescence (F) values were inhibited. The maximum quantum yield of PSII photochemistry (F/F), the maximum energy transformation potential of PSII photochemistry (F/F) and the effective quantum yield of PSII photochemistry (Φ) increased significantly, especially the latter two variables. The values of the photochemical quenching coefficient (q) and the nonphotochemical quenching (NPQ) were similar between G. mosseae inoculation and noninoculation. It could be concluded that G. mosseae inoculation could protect the photosystem II (PSII) of beach plum, enhance the efficiency of primary light energy conversion and improve the primitive response of photosynthesis under salinity stress. Meanwhile, G. mosseae inoculation was beneficial to maintain the integrity of thylakoid membrane and to protect the structure and function of chloroplast, which suggested that G. mosseae can alleviate the damage of NaCl stress to chloroplast. [ABSTRACT FROM AUTHOR]

Abstract: 5-Aminolevulinic acid (ALA) is an important plant growth regulator which is derived from 5-carbon aliphatic amino acid. The present study investigates the interaction of increasing NaCl-salinity and ALA on plant growth, leaf pigment composition, leaf and root Na+/K+ ratio and chloroplast ultrastructure in mesophyll cells of oilseed rape (Brassica napus) leaves. The plants were treated hydroponically with three different salinity levels (0, 100, 200 mM) and foliar application of ALA (30 mg l−1) simultaneously. Ten days after treatment, higher NaCl-salinity significantly reduced the plant biomass and height. However, ALA application restored the plant biomass and plant height under saline conditions. A concentration-dependent increase in Na+ uptake was observed in the aerial parts of B. napus plants. On the other hand, ALA reduced Na+ uptake, leading to a significant decrease in Na+/K+ ratio. Accumulation of Na+ augmented the oxidative stress, which was evident by electron microscopic images, highlighting several changes in cell shape and size, chloroplast swelling, increased number of plastogloubli, reduced starch granules and dilations of the thylakoids. Foliar application of ALA improved the energy supply and investment in mechanisms (higher chlorophyll and carotenoid contents, enhanced photosynthetic efficiency), reduced the oxidative stress as evident by the regular shaped chloroplasts with more intact thylakoids. On the basis of these results we can suggest that ALA is a promising plant growth regulator which can improve plant survival under salinity. [Copyright &y& Elsevier]