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Differences in plant leaf elemental contents due to seasonal climate change reflect potential plant growth strategies. However, the distribution patterns of elements mediated by seasonal climate change remain unclear. This limits assessment of plant growth status and prediction of plant growth dynamics under global climate change. We collected 41 subtropical evergreen broadleaf plant leaves (31 tree species and 10 shrub species) during the wet and dry seasons, and determined foliar contents of macro- and microelements by inductively coupled plasma mass spectrometer. Our results showed that 41 plant leaves had significantly greater macroelement contents and significantly lower microelement contents in wet season than dry season. The highest macroelement content was in tree layer plants in wet season, followed by tree layer plants in dry season and shrub layer plants in wet season, the lowest was in shrub layer plants in dry season. The highest microelement content was in tree and shrub layer plants in dry season, followed by shrub layer plants in wet season, the lowest was in tree layer plants in wet season. Our results show that macro- and microelement contents of plant leaves with different vertical structures are affected by seasonal climate change. The transition from wet to dry season was detrimental to tree layer plants growth, but had less impact on shrub layer plants growth. These findings provide valuable evidence for predicting how different vertically structured subtropical evergreen broadleaf plants can adapt to changes in wet and dry season environments and to future global climate change. [ABSTRACT FROM AUTHOR]

Many studies have investigated the photoprotective and photosynthetic capacity of plant leaves, but few have simultaneously evaluated the dynamic changes of photoprotective capacity and photosynthetic maturation of leaves at different developmental stages. As a result, the process between the decline of photoprotective substances and the onset of photosynthetic maturation during plant leaf development are still poorly understood, and the relationship between them has not been quantitatively described. In this study, the contents of photoprotective substances, photosynthetic pigment content and photosynthetic capacity of leaves at different developmental stages from young leaves to mature leaves were determined by spatio-temporal replacement in eight dominant tree species in subtropical evergreen broadleaved forests. The correlation analysis found that the data sets of anthocyanins, flavonoids, total phenolics and total antioxidant capacity were mainly distributed on one side of the symmetry axis (y  =  x), while the data sets of flavonoids, total phenolics and total antioxidant capacity were mainly distributed on both sides of the symmetry axis (y  =  x). In addition, the content of photoprotective substances in plant leaves was significantly negatively correlated with photosynthetic pigment content and photosynthetic capacity but was significantly positively correlated with dark respiration rate (Rd). When chlorophyll accumulated to ~50% of the final value, the photoprotective substance content and Rd of plant leaves reached the lowest level, and anthocyanins disappeared completely; in contrast, the photosynthetic capacity reached the highest level. Our results suggest that anthocyanins mainly play a light-shielding role in the young leaves of most plants in subtropical forests. In addition, 50% chlorophyll accumulation in most plant leaves was the basis for judging leaf photosynthetic maturity. We also believe that 50% chlorophyll accumulation is a critical period in the transition of plant leaves from high photoprotective capacity (high metabolic capacity, low photosynthetic capacity) to low photoprotective capacity (low metabolic capacity, high photosynthetic capacity). [ABSTRACT FROM AUTHOR]

Differences in plant shade tolerance constitute a major mechanism driving the succession of forest communities in subtropical forests. However, the indirect effects of differences in light requirements on the growth of mid- and late-successional tree species are unclear, and this potential growth effect has not been explained at the transcriptome level. Here, a typical mid-successional dominant tree species, Schima superba Gardn. et Champ , and a typical late-successional dominant tree species, Cryptocarya concinna Hance were used as materials and planted under 100% full light (FL) and 30% FL (low light, LL) to explore the responses of tree species in different successional stages of subtropical forests to different light environments. Transcriptome sequencing was used to analyze the expression changes in genes related to growth and photoprotection under different light environments. The young leaves of S. superba accumulated more malondialdehyde (MDA) and superoxide radicals (⁠|${\mathrm{O}}_2^{{{}^{\bullet}}^{-}}$|⁠) under LL. A lower hormone content (auxin, cytokinin, gibberellin) in the young leaves, a weaker photosynthetic capacity in the mature leaves and significant downregulation of related gene expression were also found under LL, which resulted in the total biomass of S. superba under LL being lower than that under FL. The young leaves of C. concinna had less MDA and |${\mathrm{O}}_2^{{{}^{\bullet}}^{-}}$|⁠ , and a higher hormone contents under LL than those under FL. There was no significant difference in photosynthetic capacity between mature leaves in contrasting light environments. Although the biomass of C. concinna under LL was less than that under FL, the height of C. concinna under LL was higher than that under FL, indicating that C. concinna could grow well under the two light environments. Our results describing the acclimatization of light at the physiological, molecular and transcriptome levels are important for a complete understanding of successional mechanisms. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity affords invasive plant species the ability to colonize a wide range of habitats, but physiological plasticity of their stems is seldom recognized. Investigation of the stem plasticity of invasive plant species could lead to a better understanding of their invasiveness. We performed pot experiments involving defoliation treatments and isolated culture experiments to determine whether the invasive species Mikania micrantha exhibits greater plasticity in the stems than do three non-invasive species that co-occur in southern China and then explored the mechanism underlying the modification of its stem photosynthesis. Our results showed that the stems of M. micrantha exhibited higher plasticity in terms of either net or gross photosynthetic rate in response to the defoliation treatment. These effects were positively related to an increased stem elongation rate. The enhancement of stem photosynthesis in M. micrantha resulted from the comprehensive action involving increases in the Chl a / b ratio, D1 protein and stomatal aperture, changes in chloroplast morphology and a decrease in anthocyanins. Increased plasticity of stem photosynthesis may improve the survival of M. micrantha under harsh conditions and allow it to rapidly recover from defoliation injuries. Our results highlight that phenotypic plasticity promotes the invasion success of alien plant invaders. [ABSTRACT FROM AUTHOR]

Light attenuation and antioxidation are the main mechanisms of photoprotection by anthocyanin under high light (HL) stress. Anthocyanin synthase (ANS) is the key enzyme in the downstream portion of anthocyanin synthetic pathways. To explore the role of ANS in photoprotection by anthocyanin under HL stress, homozygous ANS -deficient Arabidopsis mutants were screened from SALK_073183 and SALK_028793. Here, we obtained two deficient mutants, ans - 1 and ans - 2 , which had ANS gene expression levels equal to 5.9 and 32.9% of that of Col respectively. By analysing their physiological and biochemical responses to HL stress, we found that there were positive correlations among ANS expression level, anthocyanin content and resistance to HL. The line with the lowest ANS expression level, ans - 1 , was also the most sensitive to HL, showing the lowest anthocyanin content, chlorophyll content, F v/ F m ratio, and Rubisco content and the highest O2•− accumulation and membrane leakage rate, although it also had the highest antioxidant capacity. Experimental evidence suggests that ANS mainly regulated the light-attenuating function of anthocyanin in photoprotection under HL. Blocking excess light is an important function of anthocyanin that protects plants from HL stress, and a high antioxidant capacity cannot compensate for the absence of the light-shielding function of anthocyanin. Upon high light stress, light-shielding and antioxidation are the main mechanisms of photoprotection by anthocyanin, the final key enzyme in whose synthetic pathways is anthocyanin synthase (ANS). This investigation tackled the role of ANS in photoprotection: ANS mainly regulates the light-shielding of anthocyanin in photoprotection. Additionally, we found that light-shielding is the important function in photoprotection of anthocyanins, and high antioxidant capacity cannot compensate for the absence of the light-shielding. [ABSTRACT FROM AUTHOR]

Abstract Arbuscular mycorrhizal fungus (AMF) can relieve Cd phytotoxicity and improve plant growth, but the mechanisms involved in this process have still been not completely known. In the present work, a pot experiment was conducted to examine productions of glutathione (GSH) and phytochelatins (PCs), and absorption, chemical forms and subcellular distribution of Cd in maize (Zea mays) inoculated with or without AMF (Rhizophagus intraradices (Ri) and Glomus versiforme (Gv)) in Cd-amended soils (0, 1 and 5 mg Cd kg−1 soil). In general, both Ri and Gv inoculation dramatically enhanced biomass production and reduced Cd concentrations in shoots and roots of maize when compared to the non-mycorrhizal treatment. Moreover, both Ri and Gv symbiosis obviously increased contents of GSH and PCs, both in shoots and roots. Subcellular distribution of Cd in maize indicated that most of Cd (more than 90%) was accumulated in cell wall and soluble fraction. In addition, Cd proportions in soluble fractions in shoots of maize inoculated with Gv or Ri were considerably increased, but reduced in cell wall fractions compared to non-mycorrhizal maize, indicating that mycorrhizal symbiosis promoted Cd transfer to vacuoles. Furthermore, proportions of Cd in inorganic and water-soluble forms were declined, but elevated in pectates and proteins-integrated forms in mycorrhizal maize, which suggested that Gv and Ri could convert Cd into inactive forms. These observations could provide a further understanding of potential Cd detoxification mechanism in maize inoculated with AMF. Graphical abstract fx1 Highlights • Gv and Ri increased the contents of GSH and PCs in maize. • Gv and Ri could convert Cd into inactive forms in maize. • Gv and Ri decreased the Cd concentrations in the shoots and roots of maize. [ABSTRACT FROM AUTHOR]

The abundance of phenolic compounds (including anthocyanins) in leaves is associated with photosynthetic performance, but the regulatory mechanism is unclear. Schima superba Gardn. et Champ. and Cryptocarya concinna Hance. which exhibit distinct anthocyanin accumulation patterns, are dominant tree species in the early- and late-successional stages, respectively, of subtropical forests in China. RNA-seq and analyses of phenolic concentrations, antioxidant capacity and photosynthetic characteristics were performed on young and mature leaves of these two species under contrasting light conditions. The high-light-acclimated young leaves of S. superba and C. concinna and low-light-acclimated young leaves of C. concinna were red. These red leaves had higher ratios of electron transport rate to gross photosynthesis (ETR: P gross) and total antioxidant capacity to chlorophyll (TAC:Chl) than did the green leaves, regardless of light conditions. In addition, the red leaves had a higher expression level of the UDP-glucose:flavonoid 3-O-glucosyltransferase (UFGT) gene than did the green leaves, irrespective of light conditions. Total antioxidant capacity was positively correlated with flavonoid content in C. concinna leaves and with total phenolic content in leaves of both species under both high and low light. Consistent with the measurements of photosynthetic performance and flavonoids:Chl ratio, photosynthesis-related genes were extensively downregulated and flavonoid-pathway-related genes were extensively upregulated in young leaves relative to mature leaves. Under high and low light, both non-photochemical quenching and TAC:Chl, which serve as different types of photoprotective tools, were enhanced in young leaves of S. superba, whereas only TAC:Chl was enhanced in young leaves of C. concinna. Our results indicate that the biosynthesis of phenolic compounds in young leaves is likely enhanced by an imbalance between photosynthetic electron supply and demand and that flavonoids play a larger role in meditating photoprotection in late-successional species than in early-successional ones. [ABSTRACT FROM AUTHOR]

Seagrasses play an important role in coastal marine ecosystems, but they have been increasingly threatened by human activities. In recent years, seagrass communities have rapidly degenerated in the coastal marine ecosystems of China. To identify the reasons for the decline in seagrasses, the phytotoxic effects of trace metals (Cu, Cd and Zn) on the seagrass Thalassia hemprichii were investigated, and the environmental contents of the metals were analyzed where the seagrass grows. The results showed that leaf necrosis in T. hemprichii exposed to 0.01-0.1 mg L−1 of Cu2+ for 5 days was more serious than that in plants exposed to the same concentrations of Cd2+ and Zn2+. The chlorophyll content in T. hemprichii declined in a concentration-dependent manner after 5 days of exposure to Cu2+, Cd2+ and Zn2+. The evident reduction in ΔF/Fm’ in T. hemprichii leaves was observed at day 1 of exposure to 0.01-1.0 mg L−1 of Cu2+ and at day 3 of exposure to 0.1-1.0 mg L−1 of Cd2+. The antioxidant enzyme activities (SOD, POD and CAT) in T. hemprichii leaves exposed to the three metal ions also showed significant changes. In seawater from Xincun Bay (Hainan, China), where T. hemprichii grows, Cu had reached a concentration (i.e., 0.01 mg L−1) that could significantly reduce chlorophyll content and ΔF/Fm’ in T. hemprichii leaves. Our results indicate that Cu influences the deterioration of seagrasses in Xincun Bay. [ABSTRACT FROM AUTHOR]

To reveal effects of elevated atmospheric CO2 on tolerance to the herbicide glyphosate in the populations of goosegrass (Eleusine indica) known to have resistance to this herbicide, two biotypes of goosegrass, a resistant (R) and a susceptible (S) biotype, were analyzed after exposed to ambient (400 μmol mol-1) and elevated CO2 (800 μmol mol-1) for 25 d. The results showed that elevated CO2 had little effect on growth of both biotypes. At elevated CO2, shoot biomass of R biotype was statistically lower than of S biotype (P<0.5). The dose-response analysis showed that glyphosate tolerance was reduced by 60% in R biotype exposed to elevated Co2 while it was slightly increased in S biotype. Elevated Co2 also had more adverse effects on photosynthetic capacity of R biotype than S biotype. As a result, maximum rate of net photosynthesis (Amax) and carboxylation efficiency (CE) under elevated CO2 in R biotype were significantly lower than in S biotype (P<0.5). These results indicate that elevated atmospheric Co2 can lead to a compromise in glyphosate tolerance of R biotype associated with poor photosynthetic characteristics, and thus will affect weed management involved with herbicide resistance in prospective agricultural systems. © 2015 Friends Science Publishers [ABSTRACT FROM AUTHOR]

In order to reveal the mechanism of succession in subtropical forest along a light gradient, we investigated photosynthetic physiological responses to three light environments in five tree species including a pioneer species Pinus massoniana Lamb., two mid-successional species Schima superba Gardn. et Champ. and Castanopsis fissa (Champ. ex Benth.) Rehd. et Wils., and two late-successional species Cryptocarya concinna Hance. and Acmena acuminatissima (BI.) Merr et Perry) that were selected from Dinghu Mountain subtropical forest, South China. Results showed that,amongthe three kinds of species in all light conditions (100%,30%and 12% of full sunlight), the pioneer species had the highest photosynthetic capacity (Amax), light saturation point (LSP), carboxylation efficiency (CE) and maximum utilisation rate of triose phosphate (TPU) that characterised a strong photosynthetic capacity and high carbon dioxide uptake efficiency. However, a higher light compensation point (LCP) and dark respiration (Rd) as well as lower apparent quantum yield (AQY) indicated that the pioneer specie cannot adapt to low light conditions. Mid-successional species had photosynthetic characteristics in between pioneer and late-successional species, but had the greatest effective quantum yield of PSII (ΦPSII) and light use efficiency (LUE, expressed in terms of photosynthesis). In contrast to pioneer and mid-successional species, late-successional species had lower photosynthetic capacity and carbon uptake efficiency, but higher shade tolerance and high-light heat dissipation capacity, as characterised by higher levels of total xanthophylls cycle pigments (VAZ) and de-epoxidation state of xanthophyll cycle (DEPs). These results indicate that photosynthetic capacity decreases along the successional axis and that late-successional species have more responsive heat dissipation capability to compensate for their inferior photosynthetic capacity. [ABSTRACT FROM AUTHOR]

Alocasia macrorrhiza is a fast growing and propagating herbaceous species commonly found in South China. To determine its physiological responses to Pb and Cd stresses, the biochemical, histochemical and cytochemical changes under PbAC2 and CdCl2 phytotoxicity were detected using leaf discs as an experimental model. After leaf discs were infiltrated in different concentrations of PbAC2 and CdCl2 solutions (0, 50, 100, 150, 200μM) for 72h, the formation of reactive oxygen species (H2O2 and O2 −) in plant tissue were found to be exaggerated together with elevated tration and cell death. Changes in chlorophyll fluorescence (F v/F m, Φ PSII, q P and NPQ) imaging colours/areas of leaf discs indicated decreased photosystem II functions by both heavy metal treatments and positive reactions of antioxidants under Pb2+ stress. Results showed that fluorescent detection of hydroxylated terephthlate using terephthalic acid as s a simple, yet valuable and specific method for monitoring tion in plant tissue under heavy metal stresses. As compared with Cd2+, Pb2+ was found to be less toxic, indicating that A. macrorrhiza tissue might have a potential tolerance to Pb. [Copyright &y& Elsevier]

Chlorophyll fluorescence and antioxidative capability in detached leaves of the wild type Arabidopsis thaliana L. ecotype Landsberg erecta ( Ler) and three mutants deficient in anthocyanins biosynthesis ( tt3, tt4, and tt3tt4) were investigated during treatment with temperatures ranging 25–45 °C. In comparison with the wild type, chlorophyll fluorescence parameters Fv/Fm, ΦPSII, electron transport rate (ETR), Fv/Fo and qP in three anthocyanin-deficient mutants showed a more rapidly decreasing rate when the temperature was over 35 °C. Non-photochemical quenching (NPQ) in these mutants was almost completely lost at 44 °C, whereas the content of heat stable protein dropped and the rate of the membrane leakage increased. Fo-temperature curves were obtained by monitoring Fo levels with gradually elevated temperatures from 22 °C to 72 °C at 0.5 °C/min. The inflexion temperatures of Fo were 45.8 °C in Ler, 45.1 °C in tt3, 44.1 °C in tt4 and 42.3 °C in tt3tt4, respectively. The temperatures of maximal Fo in three mutants were 1.9–3.8 °C lower than the wild type plants. Meanwhile, three mutants had lower activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX) and an inferior scavenging capability to DPPH (1.1-diphenyl-2-picrylhy.drazyl) radical under heat stress, and in particular tt3tt4 had the lowest antioxidative potential. The results of the diaminobenzidine-H2O2 histochemical staining showed that H2O2 was accumulated in the leaf vein and mesophyll cells of mutants under treatment at 40 °C, and it was significantly presented in leaf cells of tt3tt4. The sensitivity of Arabidopsis anthocyanins-deficient mutants to high temperatures has revealed that anthocyanins in normal plants might provide protection from high temperature injury, by enhancing its antioxidative capability under high temperature stress. [ABSTRACT FROM AUTHOR]

The screening and identification of hyperaccumulators is the key to the phytoremediation of soils contaminated by heavy metal (HM). Arbuscular mycorrhizal fungus (AMF) can improve plant growth and tolerance to HM; therefore, AMF-assisted phytoextraction has been regarded as a potential technique for the remediation of HM-polluted soils. A greenhouse pot experiment was conducted to determine whether Sphagneticola calendulacea is a Cd-hyperaccumulator and to investigate the effect of the AMF- Funneliformis mosseae (FM) on plant growth and on the accumulation, subcellular distribution and chemical form of Cd in S. calendulacea grown in soils supplemented with different Cd levels. At 25, 50 and 100 mg Cd kg−1 level, S. calendulacea showed high Cd tolerance, the translocation factor and the bioconcentration factor exceeded 1, and accumulation of more than 100 mg Cd kg−1 was observed in the aboveground parts of the plant, meeting the requirements for a Cd-hyperaccumulator. Moreover, FM colonization significantly increased both biomasses and Cd concentration in S. calendulacea. After FM inoculation, the Cd concentrations and proportions increased in the cell walls, but exhibited no significant change in the organelles of the shoots. Meanwhile, FM symbiosis contributed to the conversion of Cd from highly toxic chemical forms (extracted by 80% ethanol and deionized water) to less toxic chemical forms (extracted by 1 M NaCl, 2% acetic acid, 0.6 M HCl) of Cd in the shoots. Overall, S. calendulacea is a typical Cd-hyperaccumulator, and FM symbiosis relieved the phytotoxicity of Cd and promoted plant growth and Cd accumulation, and thus greatly increasing the efficiency of phytoextraction for Cd-polluted soil. Our study provides a theoretical basis and application guidance for the remediation of Cd-contaminated soil by the symbiont of S. calendulacea with FM. Image 1 • Sphagneticola calendulacea is a typical Cd-hyperaccumulator. • FM symbiosis increased the biomass and Cd concentrations in S. calendulacea. • FM inoculation enhanced Cd conversion to less toxic chemical forms in the shoots. • FM symbiosis enhanced Cd transport to cell walls in the shoots. [ABSTRACT FROM AUTHOR]

Several auxin herbicides, such as 2, 4-D and dicamba, have been used to eradicate an exotic invasive weed Ipomoea cairica in subtropical China, but restraining the re-explosion of this weed is still a challenge. Since ethylene is one of the major intermediate functioning products during the eradication process, we explored the possibility, mechanism and efficiency of using ethephon which can release ethylene to control Ipomoea cairica. The results of the pot experiment showed that 7.2 g /L ethephon could totally kill Ipomoea cairica including the stems and roots. The water culture experiment indicated that ethephon released an abundance of ethylene directly in leaves and caused increases in electrolyte leakage, 1-aminocyclopropane-1-carboxylic acid (ACC), abscisic acid (ABA) and H2O2 and decreases in chlorophyll content and photosynthetic activity, finally leading to the death of Ipomoea cairica. The field experiment showed that the theoretical effective concentration of ethephon for controlling Ipomoea cairica (weed control efficacy, WCE = 98%) was 4.06 g/L and the half inhibitory concentration (I50) was 0.56 g/L. More than 50% of the accompanying species were insensitive to the phytotoxicity of ethephon. Therefore, ethephon is an excellent alternative herbicide for controlling Ipomoea cairica. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study was to compare the growth, community structure, and nutrient removal rates between monoculture and mixed wetlands, based on the hypothesis that it depends on the plant species used in the wetlands as to whether monoculture or mixed wetland is superior in plant growth and nutrient removal. Pilot-scale monoculture and mixed constructed wetlands were studied over 4 years. The monoculture wetland had a community height similar to the mixed wetland during the early years but a significantly lower height than the mixed wetland (P <0.05) during the last year. The mixed wetland also displayed a higher plant density than the monoculture wetland (P <0.05). The leaf area index in the monoculture wetland was significantly higher in the first year (P <0.05) and significantly lower in the later years (P <0.05) than that in the mixed wetland. The monoculture wetland had a similar vertical distribution of below-ground biomass over 4 years, while the mixed wetland showed a significant change in vertical distribution of below-ground biomass in the last 2 years. The monoculture wetland had a larger (P <0.05) above-ground biomass and a similar leaf biomass in the first year, and a smaller above-ground biomass (P <0.05) and a smaller leaf biomass (P <0.05) than the mixed wetland during the latter 2 years. The amount of standing dead mass was smaller in the mixed wetland than in the monoculture wetland (P <0.05). The mixed wetland exhibited a significantly lower NH4–N removal rate in the first year (P <0.05), and significantly higher NH4–N removal rate in the last year, when compared to the monoculture wetland (P <0.05). The study indicated that species competition and stubble growth resulted in significant differences between monoculture and mixed constructed wetlands in plant growth, community structure, and nutrient removal rates. [ABSTRACT FROM AUTHOR]

Photoprotection strategies that have evolved in plants to cope with high light (HL) stress provide plants with the ability to resist HL. However, it has not been clearly confirmed which photoprotection strategy is the major HL resistance mechanism. To reveal the major photoprotection mechanism against short-term high light (STHL), the physiological and biochemical responses of three Arabidopsis mutants (Col , chi and ans) under STHL were analyzed in this study. After STHL treatment, the most serious photosynthetic pigment damage was observed in chi plants. At the same time, the degrees of membrane and Rubisco damage in chi was the highest, followed by Col , and ans was the smallest. The results showed that ans with high antioxidant capacity showed higher resistance to STHL treatment than Col containing anthocyanins, while chi with no anthocyanin accumulation and small antioxidant capacity had the lowest resistance. In addition, the gene expression results showed that plants tend to synthesize anthocyanin precursor flavonoids with antioxidant capacity under STHL stress. To further determine the major mechanism of photoprotection under STHL, we also analyzed Arabidopsis lines (Col , CHS1 , CHS2 and tt4) that had the same anthocyanin content but different antioxidant capacities. It was found that CHS2 with high antioxidant capacity had higher cell viability, smaller maximal quantum yield of PSII photochemistry (F v /F m) reduction and less reactive oxygen species (ROS) accumulation under HL treatment of their mesophyll protoplasts. Therefore, the antioxidant capacity provided by antioxidant substances was the major mechanism of plant photoprotection under STHL treatment. • The antioxidant capacity was more important than light shielding effect under STHL. • Plants tend to synthesize anthocyanin precursor flavonoids with antioxidant capacity under STHL. • A higher antioxidant capacity correlated with a higher resistance index. • A higher antioxidant capacity correlated with a higher the mesophyll protoplast survival. [ABSTRACT FROM AUTHOR]

Theoretical and experimental studies have demonstrated that temperature is an important environmental factor that affects the regional distribution of plants. However, how to modify the distribution pattern of plants in different regions is a focus of current research. Obtain the information of cold tolerance genes from cold tolerance species, cloning genes with real cold tolerance effects is one of the most important ways to find the genes related to cold tolerance. In this study, we investigated whether transferring the VHA-c gene from Antarctic notothenioid fishes into Arabidopsis enhances freezing tolerance of Arabidopsis. The physiological response and molecular changes of VHA-c overexpressing pedigree and wildtype Arabidopsis were studied at −20 °C. The results showed that the malondialdehyde (MDA) and membrane leakage rates of WT plants were significantly higher than those of VHA-c8 and VHA-c11 plants, but the soluble sugar, soluble protein, proline and ATP contents of WT plants were significantly lower than those of VHA-c8 and VHA-c11 plants under −20 °C freezing treatment. The survival rate, VHA-c gene expression level and VHA-c protein contents of WT plants were significantly lower than those of VHA-c8 and VHA-c11 plants under −20 °C freezing treatment. Correlation analysis showed that ATP content was significantly negatively correlated with MDA and membrane leakage rate, and positively correlated with soluble sugar, soluble protein and proline content under −20 °C freezing treatment. These results demonstrated that overexpression of the VHA-c gene provided strong freezing tolerance to Arabidopsis by increasing the synthesis of ATP and improved the adaptability of plants in low temperature environment. • Transgenic Arabidopsis showed stronger resistance to freezing than WT. • Transgenic Arabidopsis can increase the content of ATP. • ATP content was negatively correlated with MDA and membrane leakage rate. • ATP content was positively correlated with osmoregulation substances. • VHA-c gene has potential application prospect in genetic improvement of cold tolerance. [ABSTRACT FROM AUTHOR]

Previous studies have suggested that high light (HL) stress causes photoinhibition in plants, while anthocyanins could protect the photosynthetic apparatus against photoinhibition. However, the photoprotection mechanism of anthocyanins is still ambiguous. We studied physiological responses and molecular changes for CHS -overexpression lines ( CHS1 , CHS2 , CHS3 ), Arabidopsis thaliana ecotype Columbia ( Col ), and T-DNA insertion lines of CHS ( tt4 ) under HL (200 μmol m −2  s −1 ) to explore the photoprotection mechanism of anthocyanins. The results showed that HL induced anthocyanin synthesis and accumulation. The leaves of CHS -overexpression lines turned reddest and the genes, including CHS, DFR, ANS, were expressed at highest levels. Thus, the CHS -overexpression lines maintained the highest photosynthetic capacity and suffered the least damage from HL of the three phenotypes. However, the CHS enzyme and anthocyanins were undetectable in tt4 during the experiment. Correspondingly, chlorophyll fluorescence parameters of tt4 declined greatly. The photosynthetic apparatus and cell membranes were also impaired dramatically. The physiological characteristics of Col were compared between CHS -overexpression lines and tt4 . Together, the results suggest that over-expression of CHS gene enhances HL resistance by synthesizing more anthocyanins, that anthocyanins enhance the adaptability of plants to HL and that they maintain photosynthetic capacity via both antioxidation and attenuation of light. [ABSTRACT FROM AUTHOR]

The successful development of photosynthetic organs is the basis of plant growth and community development. To reveal photo-acclimation to high irradiance in tree species during the course of leaf development and plant succession of subtropical forests, photosynthetic efficiency and photoprotective compounds were analyzed in young and mature leaves of three mid-successional tree species ( Castanopsis fissa , Castanopsis chinensis and Schima superba ) and three late-successional tree species ( Machilus chinensis , Cryptocarya chinensis and Cryptocarya concinna ), grown in 100% full sunlight (FL) or 30% of FL (low light, LL). Young leaves of the two species groups exhibited lower chlorophyll (Chl) content, Rubisco content, net photosynthetic rate ( P n ), carboxylation efficiency ( CE ), effective photochemical yield ( Φ PSII ), photorespiratory electron flow ( J O ), but higher dark respiration ( R d ), and ratios of carotenoids/chlorophylls (Car/Chl), anthocyanins/chlorophylls (Anth/Chl), flavonoids/chlorophylls (Flav/Chl), phenols/chlorophylls (Phen/Chl) and total antioxidant capacity/chlorophylls (TAC/Chl) than those of mature leaves, regardless of growth irradiance. Young leaves of both species groups demonstrated a higher flexibility of Anth/Chl, Flav/Chl, Phen/Chl and TAC/Chl in response to different light conditions than mature leaves. Flav/Chl in young leaves of late-successional group was remarkably higher than that of mid-successional group under the same light conditions. There was a negative correlation between antioxidant-dependent photoprotective potential and photosynthetic efficiency in young and mature leaves of the six tree species grown under either FL or LL. Our results explain partial mechanisms that lie behind the replacement of communities in subtropical forests: highly integrated photoprotective potential allows young leaves of shade-tolerant late-successional species to develop smoothly into mature organs under high irradiance. [ABSTRACT FROM AUTHOR]

Differences in response patterns to spatio-temporal changes in environmental stressors mediated by seasonal climatic differences reflect the underlying adaptation strategies of plants, and can provide key information on how tree species respond to seasonal climatic changes at different successional stages. However, in forests dominated by subtropical broadleaf evergreen species, the relationship between leaf photoprotection strategies and their construction cost strategies in different seasons remains unclear. It limits the assessment of the impact of seasonal climate change on community growth and exploration of potential drivers of community succession. In this study, we measured photoprotective substances, chlorophyll fluorescence, photosynthetic pigments and leaf construction cost (CC) in leaves of three mid-successional and three late-successional tree species in a subtropical broadleaf evergreen forest in different seasons. Our data showed that the young leaves of mid-successional trees had higher photoprotection ability in summer compared to winter, and were therefore better adapted to high temperature and high light conditions in summer, but not to low temperature and high light conditions in winter. The young leaves of late-successional trees had strong and flexible photoprotection in both summer and winter, which ensured normal growth of the young leaves under high temperature and high light in summer, and under low temperature and high light in winter. In addition, the photoprotection of the leaves was positively correlated with CC, suggesting that an increase in photoprotective capacity of plants was accompanied by an increase in its investment in CC. This was a response of the plants to environmental stress and the sacrifices it needed to make to maintain its survival. The differential growth patterns of late-successional species, which could grow normally in summer and winter, and mid-successional species, which were adapted to grow in summer but not in winter, may be key clues to the gradual replacement of mid-successional species by late-successional species. • Mid-successional tree species photoprotective potential may decrease in winter. • Late-successional tree species photoprotective potential may increase in winter. • Mid- and late-successional tree species have different CC in summer and winter. • Increased photoprotection capacity of leaves is accompanied by an increase in CC. • Mid and late-successional species have different growth patterns in summer and winter. [ABSTRACT FROM AUTHOR]

• Different photoprotection strategies for mid- and late-successional tree species. • Mid- and late-successional tree species response patterns to high-light were different. • The mid-successional tree species better tolerate high-light. • Late-successional tree species has greater restoration ability after high-light stress. Light adaptability is a major driver of succession and evolution in natural forest plant communities. However, the relationship between plants and light is contradictory; light provides energy for plant growth, but excessive light negatively affects plant growth. To reveal the pattern of plant adaptation to diurnal variation in light, photoprotection strategies were analyzed in young and mature leaves of six dominant species at two successional stages. Mature leaves of both mid- and late-successional dominant species exhibited a higher net photosynthetic rate (Pn) than young leaves. In particular, the mature leaves of the mid-successional tree species had higher high-light tolerance because of a higher Pn, water use efficiency (WUE) and electron transfer rate (ETR). In contrast, the mature leaves of the late-successional tree species had a higher restoration ability after high-light stress because of higher thermal energy dissipation and faster stomatal regulation. Young leaves of both the mid- and late-successional dominant species exhibited a higher photoprotection capability than mature leaves. The young leaves of the mid-successional tree species had higher high-light tolerance because of their highest WUE and anthocyanin/chlorophyll (Anth/Chl) and higher flavonoid/chlorophyll (Flav/Chl), total phenolics/chlorophyll (Phen/Chl) and total antioxidant capacity/chlorophyll (TAC/Chl) ratios. The young leaves of the late-successional tree species had a stronger restoration ability due to highest Flav/Chl, Phen/Chl, and TAC/Chl ratios and a higher moisture content and non-photochemical quenching coefficient (qN, NPQ). This study shows that in a high-light environment, when leaves are at the same developmental stage, mid-successional tree species better tolerate high-light, while late-successional tree species have a greater restoration ability after high-light stress. [ABSTRACT FROM AUTHOR]

In eukaryotes, the STRUCTURAL MAINTENANCE OF CHROMOSOME 5/6 (SMC5/6) complex is critical to maintaining chromosomal structures around double-strand breaks (DSBs) in DNA damage repair. However, the recruitment mechanism of this conserved complex at DSBs remains unclear. In this study, using Arabidopsis thaliana as a model, we found that SMC5/6 localization at DSBs is dependent on the protein scaffold containing INVOLVED IN DE NOVO 2 (IDN2), CELL DIVISION CYCLE 5 (CDC5), and ALTERATION/DEFICIENCY IN ACTIVATION 2B (ADA2b), whose recruitment is further mediated by DNA-damage-induced RNAs (diRNAs) generated from DNA regions around DSBs. The physical interactions of protein components including SMC5-ADA2b, ADA2b-CDC5, and CDC5-IDN2 result in formation of the protein scaffold. Further analysis indicated that the DSB localization of IDN2 requires its RNA-binding activity and ARGONAUTE 2 (AGO2), indicating a role for the AGO2-diRNA complex in this process. Given that most of the components in the scaffold are conserved, the mechanism presented here, which connects SMC5/6 recruitment and small RNAs, will improve our understanding of DNA repair mechanisms in eukaryotes., (© American Society of Plant Biologists 2022. All rights reserved. For permissions, please email: journals.permissions@oup.com.)

The content of cytochrome (cyt) bf complex is the main rate-limiting factor that determines light- and CO2-saturated photosynthetic capacity. A study of the half-life of the cyt f content in leaves was conducted whereby Pisum sativum L. plants, grown in moderately high light (HL), were transferred to low light (LL). The cyt f content in fully-expanded leaves decreased steadily over the 2 weeks after the HL-to-LL transfer, whereas control leaves in HL retained their high contents. The difference between the time courses of HL-to-LL plants and control HL plants represents the time course of loss of cyt f content, with a half-life of 1.7 days, which is >3-fold shorter than that reported for tobacco leaves at constant growth irradiance using an RNA interference approach (Hojka et al. 2014). After transfer to LL (16h photoperiod), pea plants were re-exposed to HL for 0, 1.5h or 5h during the otherwise LL photoperiod, but the cyt f content of fully-expanded leaves declined practically at the same rate regardless of whether HL was re-introduced for 0, 1.5h or 5h during each 16h LL photoperiod. It appears that fully-expanded leaves, having matured under HL, were unable to increase their cyt f content when re-introduced to HL. These findings are relevant to any attempts to maintain a high photosynthetic capacity when the growth irradiance is temporarily decreased by shading or overcast weather.

The presence of anthocyanins in young leaves plays an important role in mitigation against photodamage and allows leaves to grow and develop normally. Many studies have reported that foliar anthocyanins are distributed within the vacuoles of mesophyll cells, so we explored the novel defence style of anthocyanin-coated young leaves of Castanopsis fissa, a dominant subtropical forest tree species, via removable trichomes. Anthocyanins were distributed in C. fissa leaf trichomes, which produced a red coating for the young leaves. As young leaves developed and then matured, the thickness and density of the anthocyanin trichomes progressively decreased, the coating finally disappearing, allowing greater utilization of light by mature leaves. In addition to anthocyanins, the trichomes contained a remarkably high amount of phenolics, which enable the red coating to be more efficient in screening ultraviolet light. Compared with mature leaves, the young leaves exhibited lower photosynthetic ability, which was attributable to the reduced chlorophyll and Rubisco contents. Removal of the red coating had little effect on the photosynthetic capacity of young leaves. However, the young leaves without the coating suffered greater light-induced photoinhibition due to greater excess light entering the chloroplast and the production of H 2 O 2 Our results suggest that the anthocyanin coating is photoprotective and this anthocyanin defence style may be a metabolically cost-effective way of adjusting the anthocyanin content in response to demand., (© The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Ten anthocyanin components have been detected in roots of purple sweet potato (Ipomoea batatas Lam.) by high-performance liquid chromatography coupled to diode array detection and electrospray ionization tandem mass spectrometry. All the anthocyanins were exclusively cyanidins or peonidin 3-sophoroside-5-glucosides and their acylated derivatives. The total anthocyanin content in purple sweet potato powder obtained by solid-phase extraction was 66 mg g(-1). A strong capacity of purple sweet potato anthocyanins (PSPA) to scavenge reactive oxygen species (superoxide, hydroxyl radical) and the stable 1,1-diphenyl-2-picrylhydrazyl organic free radical was found in vitro using the electron spin resonance technique. To determine the functional roles of anthocyanins in leaves in vivo, for the first time, supplemental anthocyanins were infiltrated into leaves of Arabidopsis thaliana double mutant of the ecotype Landsberg erecta (tt3tt4) deficient in anthocyanin biosynthesis. Chlorophyll fluorescence imaging showed that anthocyanins significantly ameliorated the inactivation of photosystems II during prolonged high-light (1300 micromol m(-2) s(-1)) exposure. Comet assay of DNA revealed an obvious role of supplemental PSPA in alleviating DNA damage by high light in leaves. Our results suggest that anthocyanins could function in vitro and in vivo to alleviate the direct or indirect oxidative damage of the photosynthetic apparatus and DNA in plants caused by high-light stress.

Chlorophyll fluorescence imaging and antioxidative capability in detached leaves of the wild-type Arabidopsis thaliana ecotype Landsberg erecta (Ler) and in three mutants deficient in anthocyanin biosynthesis (tt3, tt4 and tt3tt4) were investigated under photooxidation stress induced by methyl viologen (5 μm) in the light. In comparison with the wild-type (WT) plant, photooxidation resulted in significant decreases in the contents of total phenolics and flavonoid, total antioxidative capability and chlorophyll fluorescence parameters (F v /F m , qP, Φ PSII , NPQ and ETR) as determined by chlorophyll fluorescence imaging, and in an increase in cell-membrane leakiness in the three anthocyanin mutants. The sequence of sensitivity to photooxidation in the leaves of the four phenotypes were tt3tt4 (deficient in both chalcone synthase locus (CHS) and dihydroflavonol 4-reductase locus (DFR)) > tt4 (deficient in CHS) > tt3 (deficient in DFR) > WT. The results demonstrate that anthocyanins might, along with other antioxidants, protect the photosynthetic apparatus against photooxidative damage. An interesting phenomenon was observed over the 270 min of the photooxidative treatment, that is, fluorescence imaging revealed that qP, Φ PSII and ETR appeared in three phases (fall → partial recovery → rapid fall). This was considered to be a modulation of reversible deactivation in PSII to cope with the moderate oxidative stress in the first two stages of short-term treatment (<150 min), followed finally by damage to PSII under severe oxidative stress with prolonged treatment.

In the present study, both electron spin resonance (ESR) and chemical detection confirmed that lutein [extracted from alfalfa (Medicago sativa L.)], the most abundant xanthophyll in thylakoids of chloroplasts, could serve as an antioxidant to scavenge reactive oxygen species (ROS) in vitro. Lutein exhibited a greater capacity for scavenging hydroxyl (OH · ) and superoxide (O 2 · - ) radicals than β-carotene at the same concentration, whereas the opposite trend was observed in the capacity for scavenging singlet oxygen ( 1 O 2 ). The capacity of lutein for scavenging ROS from high to low is OH · > O 2 · - under severe stress. This hypothesis is consistent with our previous report that the lut2 (lutein-deficient) Arabidopsis mutant is more susceptible to damage than the npq1 (lutein-replete but violaxanthin de-epoxidase-deficient) Arabidopsis mutant under severe stress during exposure to high light intensity at low temperature (Peng and Gilmore 2003).1 O 2 . We hypothesise that lutein plays an important photoprotective role in scavenging O 2 · - and OH · under severe stress. This hypothesis is consistent with our previous report that the lut2 (lutein-deficient) Arabidopsis mutant is more susceptible to damage than the npq1 (lutein-replete but violaxanthin de-epoxidase-deficient) Arabidopsis mutant under severe stress during exposure to high light intensity at low temperature (Peng and Gilmore 2003).

This study compared the response to methyl viologen (MV)-induced photooxidation in wild-type barley (wt), and both its chlorina f104-nuclear gene mutant (that restricts Chl a and b synthesis) and its f2-nuclear gene mutant (that inhibits all Chl b synthesis). Without MV, the f2 mutant showed the highest sensitivity to high light, with Fv/Fm being reduced by 80% after 80 min of irradiation. There was little difference in response to high light without MV between f104 and wt. After vacuum infiltration with 100 μM MV and exposure to high light, f104 exhibited the highest sensitivity while f2 was the most tolerant to the photooxidation effects. 77K fluorescence spectral analysis indicated that PSII of f104 was especially damaged, as evidenced by the appearance of a new Chl a emission band around 700 nm at the expense of the F685 and F695 bands from the PSII core-inner antenna. With MV, chlorophyll degraded more rapidly in f104 than in either f2 or wt. During MV treatment, zeaxanthin content increased significantly during the initial period of exposure (0-20 min) in all strains, but decreased sharply in f104 after longer exposure time (20-80 min). β-Carotene, on a chlorophyll basis, was not much changed under high light without MV, but with MV it decreased significantly, mostly in f104, intermediately in f2 and least in wt. We conclude that the light-sensitive chlorosis phenotype of f104 is exacerbated by MV-induced photooxidation.