Unveiling large charge transfer character of PSII in an iron-deficient cyanobacterial membrane: A Stark fluorescence spectroscopy study.

In this work, we applied Stark fluorescence spectroscopy to an iron-stressed cyanobacterial membrane to reveal key insights about the electronic structures and excited state dynamics of the two important pigment-protein complexes, IsiA and PSII, both of which prevail simultaneously within the membrane during iron deficiency and whose fluorescence spectra are highly overlapped and hence often hardly resolved by conventional fluorescence spectroscopy. Thanks to the ability of Stark fluorescence spectroscopy, the fluorescence signatures of the two complexes could be plausibly recognized and disentangled. The systematic analysis of the SF spectra, carried out by employing standard Liptay formalism with a realistic spectral deconvolution protocol, revealed that the IsiA in an intact membrane retains almost identical excited state electronic structures and dynamics as compared to the isolated IsiA we reported in our earlier study. Moreover, the analysis uncovered that the excited state of the PSII subunit of the intact membrane possesses a significantly large CT character. The observed notably large magnitude of the excited state CT character may signify the supplementary role of PSII in regulative energy dissipation during iron deficiency.

Application of Chlorophyll Fluorescence Analysis Technique in Studying the Response of Lettuce (Lactuca sativa L.) to Cadmium Stress.

To reveal the impact of cadmium stress on the physiological mechanism of lettuce, simultaneous determination and correlation analyses of chlorophyll content and photosynthetic function were conducted using lettuce seedlings as the research subject. The changes in relative chlorophyll content, rapid chlorophyll fluorescence induction kinetics curve, and related chlorophyll fluorescence parameters of lettuce seedling leaves under cadmium stress were detected and analyzed. Furthermore, a model for estimating relative chlorophyll content was established. The results showed that cadmium stress at 1 mg/kg and 5 mg/kg had a promoting effect on the relative chlorophyll content, while cadmium stress at 10 mg/kg and 20 mg/kg had an inhibitory effect on the relative chlorophyll content. Moreover, with the extension of time, the inhibitory effect became more pronounced. Cadmium stress affects both the donor and acceptor sides of photosystem II in lettuce seedling leaves, damaging the electron transfer chain and reducing energy transfer in the photosynthetic system. It also inhibits water photolysis and decreases electron transfer efficiency, leading to a decline in photosynthesis. However, lettuce seedling leaves can mitigate photosystem II damage caused by cadmium stress through increased thermal dissipation. The model established based on the energy captured by a reaction center for electron transfer can effectively estimate the relative chlorophyll content of leaves. This study demonstrates that chlorophyll fluorescence techniques have great potential in elucidating the physiological mechanism of cadmium stress in lettuce, as well as in achieving synchronized determination and correlation analyses of chlorophyll content and photosynthetic function.

Trichoderma asperellum boosts nitrogen accumulation and photosynthetic capacity of wolfberry (Lycium chinense) under saline soil stress.

Trichoderma can promote plant growth under saline stress, but the mechanisms remain to be revealed. In this study, we investigate photosynthetic gas exchange, photosystem II (PSII) performance, nitrogen absorption and accumulation in a medicinal plant wolfberry (Lycium chinense) in saline soil supplemented with Trichoderma biofertilizer (TF). Larger nitrogen and biomass accumulation were found in plants supplemented with TF than with organic fertilizer (OF), suggesting that Trichoderma asperellum promoted plant growth and nitrogen accumulation under saline stress. T. asperellum strengthened root nitrogen (N) absorption according to greater increased root NH4+ and NO3- influxes under supplement with TF than OF, while nitrogen assimilative enzymes such as nitrate reductase, nitrite reductase and glutamine synthetase activities in roots and leaves were also stimulated. Thus, the elevated N accumulation derived from the induction of T. asperellum on nitrogen absorption and assimilation. Greater increased photosynthetic rate (Pn) and photosynthetic N-use efficiency under supplement with TF than OF illustrated that T. asperellum enhanced photosynthetic capacity and N utilization under saline stress. Although increased leaf stomatal conductance contributed to carbon (C) isotope fractionation under TF supplement, leaf 13C abundance was significantly increased by supplement with TF rather than OF, indicating that T. asperellum raised CO2 assimilation to a greater extent, reducing C isotope preference. Trichoderma asperellum optimized electron transport at PSII donor and acceptor sides under saline stress because of lower K and J steps in chlorophyll fluorescence transients under supplement with TF than OF. The amount of PSII active reaction centers was also increased by T. asperellum. Thus, PSII performance was upgraded, consistent with greater heightened delayed chlorophyll fluorescence transients and I1 peak under supplement with TF than OF. In summary, TF acted to increase N nutrient acquisition and photosynthetic C fixation resulting in enhanced wolfberry growth under saline soil stress.

Toxicity, physiological, and morphological alterations of Indian camphorweed (Pluchea indica) in response to excess copper.

Indian camphorweed (Pluchea indica (L.) Less.) is used as herbal tea due to the presence of volatile aromatic oils and several phytochemical compounds. The aim of this study was to assess the impact of copper (Cu) contamination on the physiology and morphology of P. indica, and the health risks associated with its consumption as tea. The cuttings of P. indica were subjected to 0 mM (control), 5 mM (low Cu), and 20 mM (excess Cu) of CuSO4 treatments for 1, 2, and 4 weeks. Thereafter, Cu contamination as well as physiological and morphological parameters were assessed. Cu accumulation was higher in the root tissues of plants (25.8 folds higher as compared to the leaves) grown under 20 mM CuSO4 for 4 weeks. This increased Cu accumulation resulted in the inhibition of root length, root fresh weight, and root dry weight. Cu concentration was found maximum (1.36 µg g-1 DW) in the leaf tissues under 20 mM Cu exposure for 4 weeks, with the highest target hazard quotient (THQ = 1.85), whereas Cu was not detected in control. Under exposure to 20 mM Cu treatment for 4 weeks, leaf greenness, maximum quantum yield of photosystem II, and photon yield of photosystem II diminished by 21.4%, 16.1%, and 22.4%, respectively, as compared to the control. Leaf temperature was increased by 2.5 °C, and the crop stress index (CSI) exceeded 0.6 when exposed to 20 mM Cu treatment for 2 and 4 weeks; however, the control had a CSI below 0.5. This led to a reduced transpiration rate and stomatal conductance. In addition, the net photosynthetic rate was also found sensitive to Cu treatment, which resulted in decreased shoot and root growth. Based on the key results, it can be suggested that P. indica herbal tea derived from the foliage of plants grown under a 5 mM Cu level (0.75 µg g-1 DW) with a target hazard quotient below one aligns with the recommended dietary intake of Cu in leafy vegetables. The study recommends choosing cuttings from plants with a small canopy as plant material in the greenhouse microclimates to validate the growth performance in the Cu-contaminated soil and simulate the natural shrub architecture and life cycle.

Exposed anthocyanic leaves of Prunus cerasifera are special shade leaves with high resistance to blue light but low resistance to red light against photoinhibition of photosynthesis.

BACKGROUND AND AIMS: The photoprotective role of foliar anthocyanins has long been ambiguous: exacerbating, being indifferent to or ameliorating the photoinhibition of photosynthesis. The photoinhibitory light spectrum and failure to separate photo-resistance from repair, as well as the different methods used to quantify the photo-susceptibility of the photosystems, could lead to such a discrepancy. METHODS: We selected two congeneric deciduous shrubs, Prunus cerasifera with anthocyanic leaves and Prunus triloba with green leaves, grown under identical growth conditions in an open field. The photo-susceptibilities of photosystem II (PSII) and photosystem I (PSI) to red light and blue light, in the presence of lincomycin (to block the repair), of exposed leaves were quantified by a non-intrusive P700+ signal from PSI. Leaf absorption, pigments, gas exchange and Chl a fluorescence were also measured. KEY RESULTS: The content of anthocyanins in red leaves (P. cerasifera) was >13 times greater than that in green leaves (P. triloba). With no difference in maximum quantum efficiency of PSII photochemistry (Fv/Fm) and apparent CO2 quantum yield (AQY) in red light, anthocyanic leaves (P. cerasifera) showed some shade-acclimated suites, including lower Chl a/b ratio, lower photosynthesis rate, lower stomatal conductance and lower PSII/PSI ratio (on an arbitrary scale), compared with green leaves (P. triloba). In the absence of repair of PSII, anthocyanic leaves (P. cerasifera) showed a rate coefficient of PSII photoinactivation (ki) that was 1.8 times higher than that of green leaves (P. triloba) under red light, but significantly lower (-18 %) under blue light. PSI of both types of leaves was not photoinactivated under blue or red light. CONCLUSIONS: In the absence of repair, anthocyanic leaves exhibited an exacerbation of PSII photoinactivation under red light and a mitigation under blue light, which can partially reconcile the existing controversy in terms of the photoprotection by anthocyanins. Overall, the results demonstrate that appropriate methodology applied to test the photoprotection hypothesis of anthocyanins is critical.

Shading-Dependent Greening Process of the Leaves in the Light-Sensitive Albino Tea Plant 'Huangjinya': Possible Involvement of the Light-Harvesting Complex II Subunit of Photosystem II in the Phenotypic Characteristic.

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

CsCIPK11-Regulated Metalloprotease CsFtsH5 Mediates the Cold Response of Tea Plants.

Photosystem II repair in chloroplasts is a critical process involved in maintaining a plant's photosynthetic activity under cold stress. FtsH (filamentation temperature-sensitive H) is an essential metalloprotease that is required for chloroplast photosystem II repair. However, the role of FtsH in tea plants and its regulatory mechanism under cold stress remains elusive. In this study, we cloned a FtsH homolog gene in tea plants, named CsFtsH5, and found that CsFtsH5 was located in the chloroplast and cytomembrane. RT-qPCR showed that the expression of CsFtsH5 was increased with leaf maturity and was significantly induced by light and cold stress. Transient knockdown CsFtsH5 expression in tea leaves using antisense oligonucleotides resulted in hypersensitivity to cold stress, along with higher relative electrolyte leakage and lower Fv/Fm values. To investigate the molecular mechanism underlying CsFtsH5 involvement in the cold stress, we focused on the calcineurin B-like-interacting protein kinase 11 (CsCIPK11), which had a tissue expression pattern similar to that of CsFtsH5 and was also upregulated by light and cold stress. Yeast two-hybrid and dual luciferase (Luc) complementation assays revealed that CsFtsH5 interacted with CsCIPK11. Furthermore, the Dual-Luc assay showed that CsCIPK11-CsFtsH5 interaction might enhance CsFtsH5 stability. Altogether, our study demonstrates that CsFtsH5 is associated with CsCIPK11 and plays a positive role in maintaining the photosynthetic activity of tea plants in response to low temperatures.

Priming Potato Plants with Melatonin Protects Stolon Formation under Delayed Salt Stress by Maintaining the Photochemical Function of Photosystem II, Ionic Homeostasis and Activating the Antioxidant System.

Melatonin is among one of the promising agents able to protect agricultural plants from the adverse action of different stressors, including salinity. We aimed to investigate the effects of melatonin priming (0.1, 1.0 and 10 µM) on salt-stressed potato plants (125 mM NaCl), by studying the growth parameters, photochemical activity of photosystem II, water status, ion content and antioxidant system activity. Melatonin as a pleiotropic signaling molecule was found to decrease the negative effect of salt stress on stolon formation, tissue water content and ion status without a significant effect on the expression of Na+/H+-antiporter genes localized on the vacuolar (NHX1 to NHX3) and plasma membrane (SOS1). Melatonin effectively decreases the accumulation of lipid peroxidation products in potato leaves in the whole range of concentrations studied. A melatonin-induced dose-dependent increase in Fv/Fm together with a decrease in uncontrolled non-photochemical dissipation Y(NO) also indicates decreased oxidative damage. The observed protective ability of melatonin was unlikely due to its influence on antioxidant enzymes, since neither SOD nor peroxidase were activated by melatonin. Melatonin exerted positive effects on the accumulation of water-soluble low-molecular-weight antioxidants, proline and flavonoids, which could aid in decreasing oxidative stress. The most consistent positive effect was observed on the accumulation of carotenoids, which are well-known lipophilic antioxidants playing an important role in the protection of photosynthesis from oxidative damage. Finally, it is possible that melatonin accumulated during pretreatment could exert direct antioxidative effects due to the ROS scavenging activity of melatonin molecules.

Toward a Holistic Understanding and Models of Nonphotochemical Quenching Effects on In Vivo Fluorometry of Chlorophyll a in Coastal Waters.

Nonphotochemical quenching (NPQ) is known to depress in vivo fluorescence (IVF) of chlorophyll a (Chla) in aquatic environments, which makes it difficult to interpret the hour-to-hour variations in Chla measured by in situ fluorometers. We hypothesized that ratios between quenched and unquenched IVF are a function of both NPQ and photochemical quenching. In this study, two diatom model species Thalassiosira pseudonana (CCMP1335) and Thalassiosira weissflogii (CCMP1047) incubated under a sinusoidal light:dark cycle were studied; IVF was recorded continuously, and Chla and photo-physiological variables were measured seven times a day. The maximal decline in Chla-specific IVF (IVFB ) attributable to quenching was 50% under the experimental settings. An NPQ and photochemical quenching-based modeling equation exhibited a better match to the measured IVFB than equations representing the sole NPQ effect. Photochemical quenching induced by measuring light beam varied substantially during the day, and the part of the model for this process is excitation intensity-dependent (which is differed between models of in situ fluorometers, implying no straightforward method to correct Chla for all instrument models, instrument-specific parameterization is required). The forms of the IVFB -light relationship are discussed as well. The findings foster a holistic understanding of NPQ effects on in vivo Chla fluorometry.

High boron stress leads to sugar beet (Beta vulgaris L.) toxicity by disrupting photosystem â ¡.

This sugar beet acts as a soil remediator in areas where there are high levels of boron (B) in the soil, since it has a high requirement of boron (B) for growth, and has strong resistance to high B levels. Although B toxicity in different plants has been widely researched, little is known about the response of photosystem II (PSII) activity in sugar beet leaves to B toxicity at present. To clarify the growth and photosynthetic physiological response of sugar beet to B toxicity, the effects of different concentrations of H3BO3 (0.05, 1.5, 2.5,3.5 mM) on the growth, photosynthetic characteristics and antioxidant defense system of sugar beet seedlings were investigated by hydroponic experiments. In the present study, high B stress inhibited the growth of sugar beet and significantly decreased the biomass of the plants. There was a remarkable increase in the accumulation of B in the shoots, which affected photosynthesis and decreased the photosynthetic pigments. As B toxicity increased, leaf PSII activities and maximum photochemical efficiency of PSII (Fv/Fm) showed a tendency to decrease; at the same time, the photosynthetic performance index based on absorbed light energy (PIABS) decreased as well. Meanwhile, the energy allocation parameters of the PSII reaction center were changed, the light energy utilization capacity and the energy used for electron transfer were reduced and the thermal dissipation was increased at the same time. Furthermore, B toxicity decreased catalase (CAT) activity, increased peroxidase (POD) and superoxide dismutase (SOD) activities, and increased malondialdehyde (MDA) accumulation. According to the results obtained in this study, high B concentrations reduced the rate of photosynthesis and fluorescence, thus weakened antioxidant defense systems, and therefore inhibited the growth of sugar beet plants. Thus, in high B areas, sugar beet possesses excellent tolerance to high B levels and has a high B translocation capacity, so it can be used as a phytoremediation tool. This study provides a basis for the feasibility of sugar beet resistant to high B environments.

A Hormetic Spatiotemporal Photosystem II Response Mechanism of Salvia to Excess Zinc Exposure.

Exposure of Salvia sclarea plants to excess Zn for 8 days resulted in increased Ca, Fe, Mn, and Zn concentrations, but decreased Mg, in the aboveground tissues. The significant increase in the aboveground tissues of Mn, which is vital in the oxygen-evolving complex (OEC) of photosystem II (PSII), contributed to the higher efficiency of the OEC, and together with the increased Fe, which has a fundamental role as a component of the enzymes involved in the electron transport process, resulted in an increased electron transport rate (ETR). The decreased Mg content in the aboveground tissues contributed to decreased chlorophyll content that reduced excess absorption of sunlight and operated to improve PSII photochemistry (ΦPSII), decreasing excess energy at PSII and lowering the degree of photoinhibition, as judged from the increased maximum efficiency of PSII photochemistry (Fv/Fm). The molecular mechanism by which Zn-treated leaves displayed an improved PSII photochemistry was the increased fraction of open PSII reaction centers (qp) and, mainly, the increased efficiency of the reaction centers (Fv'/Fm') that enhanced ETR. Elemental bioimaging of Zn and Ca by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) revealed their co-localization in the mid-leaf veins. The high Zn concentration was located in the mid-leaf-vein area, while mesophyll cells accumulated small amounts of Zn, thus resembling a spatiotemporal heterogenous response and suggesting an adaptive strategy. These findings contribute to our understanding of how exposure to excess Zn triggered a hormetic response of PSII photochemistry. Exposure of aromatic and medicinal plants to excess Zn in hydroponics can be regarded as an economical approach to ameliorate the deficiency of Fe and Zn, which are essential micronutrients for human health.

Compounds to mitigate cyanobacterial blooms affect growth and toxicity of Microcystis aeruginosa.

Numerous products and techniques are used to combat harmful cyanobacterial blooms in lakes. In this study, we tested nine products, the phosphate binders Phoslock® and Aqual-PTM, the coagulant chitosan, the phosphorus binder and coagulant aluminum salts (aluminum sulphate and sodium aluminate), the copper-based algicides SeClear, Captain® XTR and CuSO4·5H2O, the antibiotic Streptomycin and the oxidant hydrogen peroxide (H2O2) on their efficiency to manage the cyanobacterium Microcystis aeruginosa (M. aeruginosa). To this end, 7 days of laboratory experiments were conducted and effects were determined on chlorophyll-a, photosystem II efficiency (PSII), soluble reactive phosphorus (SRP) and intracellular and extracellular microcystin (MC) concentrations. The algicides, chitosan and H2O2 were the most powerful in reducing cyanobacteria biomass. Biomass reductions compared to the controls yielded: Chitosan (99.8%) > Hydrogen peroxide (99.6%) > Captain XTR (98.2%) > SeClear (98.1%) > CuSO4·5H2O (97.8%) > Streptomycin (86.6%) > Phoslock® (42.6%) > Aqual-PTM (28.4%) > alum (5.5%). Compounds that caused the largest reductions in biomass also strongly lowered photosystem II efficiency, while the other compounds (Phoslock®, Aqual-PTM, aluminum salts) had no effect on PSII, but strongly reduced SRP. Intracellular MC concentration followed the biomass patterns, extracellular MC was generally lower at higher doses of algicides, chitosan and H2O2 after one week. Recovery of PSII was observed in most algicides and chitosan, but not at the highest doses of SeClear and in all streptomycin treatments. Our results revealed that M. aeruginosa can be killed rapidly using several compounds, that in some treatments already signs of recovery occurred within one week. P fixatives are efficient in reducing SRP, and thus acting via resource suppression, which potentially may provide an addition to fast-acting algicides that kill most of the cells, but allow rapid regrowth as sufficient nutrients remain.

Photosynthetic carbon and nitrogen metabolism of Camellia oleifera Abel during acclimation to low light conditions.

Tea-oil tree (Camellia oleifera Abel) is an important woody oil crop with high economic value. However, it has low photosynthetic production considering the low light intensity of its growth environment. To understand the acclimation mechanism of tea-oil trees to low light conditions, three light intensity treatments were conducted: high light (450-500 µmol. m-2. s-1), medium light (180-200 µmol. m-2. s-1), and low light (45-50 µmol. m-2. s-1). The carbon (C) and nitrogen (N) metabolism network were constructed by investigating the leaf anatomy, photosynthetic characteristics, N partitioning, transcriptome and metabolome. Results demonstrated that a larger proportion light energy was used for photochemical reactions in an environment with lower light intensity, which resulted in an increase in photosystem II photochemical efficiency and instantaneous light use efficiency (LUE) at the leaf level. As the light intensity increased, decreased electron transfer and carboxylation efficiencies, photorespiration and dark respiration rates, LUE at plant level, and N use efficiency (PNUE) were observed. Leaves trended to harvest more light using higher expression levels of light-harvesting protein genes, higher chlorophyll content, more granum and more tightly stacked granum lamella under lower light intensity. At transcriptional and metabolic levels, the TCA cycle, and the synthesis of starch and saccharides were weakened as light intensity decreased, while the Calvin cycle did not show the regularity between different treatments. Less N was distributed in Rubisco, respiration, and cell wall proteins as light decreased. Storage N was prominently accumulated in forms of amino acids (especially L-arginine) and amino acid derivatives as under medium and low light environments, to make up for C deficiency. Therefore, tea-oil trees actively improve light-harvesting capacity and enlarges the storage N pool to adapt to a low light environment, at the cost of a decrease of photosynthetic C assimilation and PNUE.

Calcium nanoparticles (Ca-NPs) improve drought stress tolerance in Brassica napus by modulating the photosystem II, nutrient acquisition and antioxidant performance.

Foliar-application of nano-particles enhanced the foliar nutrient status and crop growth and yield. It is hypothesized that being second messenger molecule, supplementation of Ca2+ via calcium nanoparticles (Ca-NPs) can trigger various signaling pathways of physiological processes which can lead to alleviate the adverse effects of drought stress on the growth of canola (Brassica napus L.). Nano-enabled foliar-application could be an ideal strategy for advancing agricultural productivity. The present study explored the role of calcium nanoparticles (Ca-NPs) in alleviating drought stress in hydroponic Brassica napus (B. napus) plants. The foliar applied Ca-NPs were spherically shaped with an average size of 86 nm. Foliar application of 100 mg L-1 Ca-NPs enhanced biomass of canola plants and considered as optimal dose. Ca-NPs at 100 mg L-1 has a greater favorable impact on mesophyll ultrastructure, PSI and PSII efficacy, gas exchange parameters, chlorophyll content, and mineral absorption. The Ca-NPs treatment increased NPQ and Y(NPQ) under drought condition, indicating a higher PSII protective response to stressed conditions with better heat dissipation as a photoprotective component of NPQ. Ca-NPs application also reduced oxidative stress damage as measured by a reduction in reactive oxygen species (ROS) generation in terms of hydrogen peroxide and malondialdehyde (H2O2 and MDA). Furthermore, Ca-NPs induced drought tolerance response corresponded to an increased in key antioxidative defense enzymes (SOD, POD, CAT, APX), as well as non-enzymatic components (protease, lipoxygenase, proline, total soluble protein contents, endogenous hormonal biosynthesis), and secondary metabolite expression in B. napus plants. Taken together, the results of this study offer new insights into the physiological and molecular mechanisms by which B. napus responds to Ca-NPs exposure.

Morphological, physiological, and secondary metabolic responses of Taraxacum officinale to salt stress.

Salt stress has a major effect on growth and secondary metabolism in medicinal plants, however, the effect of salt stress on Taraxacum officinale F. H. Wigg. is still scarce. In this study, we evaluated the effects of salt stress on the physiology, morphology, phenolic acid accumulation, and expression of genes involved in phenolic acid biosynthesis in T. officinale. We found that plants grew well at 1 g kg-1 NaCl, and the state of photosystem Ⅱ (PSⅡ) and the organization of the chloroplasts at 0.5 g kg-1 NaCl showed no significant differences compared with the control. However, 2 g kg-1 and 4 g kg-1 NaCl inhibited growth and accelerated leaf senescence. At 4 g kg-1 NaCl, the fresh and dry weights decreased to 28% and 42% of the control, while chlorosis and necrosis were observed on the leaves. Furthermore, up-regulation of the expression of ToC3'H corresponded with an increase in the levels of caffeoylquinic acids (chlorogenic acid and isochlorogenic acid A) at NaCl concentration ≤ 1 g kg-1. Expressions of four phenolic acid biosynthesis genes, ToC4H, To4CL, ToHCT, and ToHQT, were down-regulated with increasing NaCl concentrations, consistent with the observed decreases in caftaric and cichoric acids. In summary, cultivation of T. officinale under mild salt stress (NaCl ≤ 1 g kg-1) is feasible and facilitates the accumulation of caffeoylquinic acids; thus this species may be recommended for saline soils.

High-Light-Induced Degradation of Photosystem II Subunits' Involvement in the Albino Phenotype in Tea Plants.

The light-sensitive (LS) albino tea plant grows albinic shoots lacking chlorophylls (Chls) under high-light (HL) conditions, and the albinic shoots re-green under low light (LL) conditions. The albinic shoots contain a high level of amino acids and are preferential materials for processing quality green tea. The young plants of the albino tea cultivars are difficult to be cultivated owing to lacking Chls. The mechanisms of the tea leaf bleaching and re-greening are unknown. We detected the activity and composition of photosystem II (PSII) subunits in LS albino tea cultivar "Huangjinya" (HJY), with a normal green-leaf cultivar "Jinxuan" (JX) as control so as to find the relationship of PSII impairment to the albino phenotype in tea. The PSII of HJY is more vulnerable to HL-stress than JX. HL-induced degradation of PSII subunits CP43, CP47, PsbP, PsbR. and light-harvest chlorophyll-protein complexes led to the exposure and degradation of D1 and D2, in which partial fragments of the degraded subunits were crosslinked to form larger aggregates. Two copies of subunits PsbO, psbN, and Lhcb1 were expressed in response to HL stress. The cDNA sequencing of CP43 shows that there is no difference in sequences of PsbC cDNA and putative amino acids of CP43 between HJY and JX. The de novo synthesis and/or repair of PSII subunits is considered to be involved in the impairment of PSII complexes, and the latter played a predominant role in the albino phenotype in the LS albino tea plant.

Pyruvate, phosphate dikinase regulatory protein impacts light response of C4 photosynthesis in Setaria viridis.

In C4 plants, the pyruvate (Pyr), phosphate dikinase regulatory protein (PDRP) regulates the activity of the C4 pathway enzyme Pyr, phosphate dikinase (PPDK) in a light-/dark-dependent manner. The importance of this regulatory action to C4 pathway function and overall C4 photosynthesis is unknown. To resolve this question, we assessed in vivo PPDK phospho-regulation and whole leaf photophysiology in a CRISPR-Cas9 PDRP knockout (KO) mutant of the NADP-ME C4 grass green millet (Setaria viridis). PDRP enzyme activity was undetectable in leaf extracts from PDRP KO lines. Likewise, PPDK phosphorylated at the PDRP-regulatory Thr residue was immunologically undetectable in leaf extracts. PPDK enzyme activity in rapid leaf extracts was constitutively high in the PDRP KO lines, irrespective of light or dark pretreatment of leaves. Gas exchange analysis of net CO2 assimilation revealed PDRP KO leaves had markedly slower light induction kinetics when leaves transition from dark to high-light or low-light to high-light. In the initial 30 min of the light induction phase, KO leaves had an ∼15% lower net CO2 assimilation rate versus the wild-type (WT). Despite the impaired slower induction kinetics, we found growth and vigor of the KO lines to be visibly indistinguishable from the WT when grown in normal air and under standard growth chamber conditions. However, the PDRP KO plants grown under a fluctuating light regime exhibited a gradual multi-day decline in Fv/Fm, indicative of progressive photosystem II damage due to the absence of PDRP. Collectively, our results demonstrate that one of PDRP's functions in C4 photosynthesis is to ensure optimal photosynthetic light induction kinetics during dynamic changes in incident light.

High non-photochemical quenching of VPZ transgenic potato plants limits CO2 assimilation under high light conditions and reduces tuber yield under fluctuating light.

Under natural conditions, photosynthesis has to be adjusted to fluctuating light intensities. Leaves exposed to high light dissipate excess light energy in form of heat at photosystem II (PSII) by a process called non-photochemical quenching (NPQ). Upon fast transition from light to shade, plants lose light energy by a relatively slow relaxation from photoprotection. Combined overexpression of violaxanthin de-epoxidase (VDE), PSII subunit S (PsbS) and zeaxanthin epoxidase (ZEP) in tobacco accelerates relaxation from photoprotection, and increases photosynthetic productivity. In Arabidopsis, expression of the same three genes (VPZ) resulted in a more rapid photoprotection but growth of the transgenic plants was impaired. Here we report on VPZ expressing potato plants grown under various light regimes. Similar to tobacco and Arabidopsis, induction and relaxation of NPQ was accelerated under all growth conditions tested, but did not cause an overall increased photosynthetic rate or growth of transgenic plants. Tuber yield of VPZ expressing plants was unaltered as compared to control plants under constant light conditions and even decreased under fluctuating light conditions. Under control conditions, levels of the phytohormone abscisic acid (ABA) were found to be elevated, indicating an increased violaxanthin availability in VPZ plants. However, the increased basal ABA levels did not improve drought tolerance of VPZ transgenic potato plants under greenhouse conditions. The failure to benefit from improved photoprotection is most likely caused by a reduced radiation use efficiency under high light conditions resulting from a too strong NPQ induction. Mitigating this negative effect in the future might help to improve photosynthetic performance in VPZ expressing potato plants.

Does silicon really matter for the photosynthetic machinery in plants ?

Silicon (Si) is known to alleviate the adverse impact of different abiotic and biotic stresses by different mechanisms including morphological, physiological, and genetic changes. Photosynthesis, one of the most important physiological processes in the plant is sensitive to different stress factors. Several studies have shown that Si ameliorates the stress effects on photosynthesis by protecting photosynthetic machinery and its function. In stressed plants, several photosynthesis-related processes including PSII maximum photochemical quantum yield (Fv/Fm), the yield of photosystem II (φPSII), electron transport rates (ETR), and photochemical quenching (qP) were observed to be regulated when supplemented with Si, which indicates that Si effectively protects the photosynthetic machinery. In addition, studies also suggested that Si is capable enough to maintain the uneven swelling, disintegrated, and missing thylakoid membranes caused during stress. Furthermore, several photosynthesis-related genes were also regulated by Si supplementation. Taking into account the key impact of Si on the evolutionarily conserved process of photosynthesis in plants, this review article is focused on the aspects of silicon and photosynthesis interrelationships during stress and signaling pathways. The assemblages of this discussion shall fulfill the lack of constructive literature related to the influence of Si on one of the most dynamic and important processes of plant life i.e. photosynthesis.

Insight into Details of the Photosynthetic Light Reactions and Selected Metabolic Changes in Tomato Seedlings Growing under Various Light Spectra.

The objective of our study was to characterise the growth of tomato seedlings under various light spectra, but special attention has been paid to gaining a deeper insight into the details of photosynthetic light reactions. The following light combinations (generated by LEDs, constant light intensity at 300 µmol m-2 s-1) were used: blue/red light; blue/red light + far red; blue/red light + UV; white light that was supplemented with green, and white light that was supplemented with blue. Moreover, two combinations of white light for which the light intensity was changed by imitating the sunrise, sunset, and moon were also tested. The reference point was also light generated by high pressure sodium lamps (HPS). Plant growth/morphological parameters under various light conditions were only partly correlated with the photosynthetic efficiency of PSI and PSII. Illumination with blue/red as the main components had a negative effect on the functioning of PSII compared to the white light and HPS-generated light. On the other hand, the functioning of PSI was especially negatively affected under the blue/red light that was supplemented with FR. The FT-Raman studies showed that the general metabolic profile of the leaves (especially proteins and ß-carotene) was similar in the plants that were grown under the HPS and under the LED-generated white light for which the light intensity changed during a day. The effect of various light conditions on the leaf hormonal balance (auxins, brassinosteroids) is also discussed.