Showing papers on "Photosynthesis published in 2023"

Foliar application of silicon-based nanoparticles improve the adaptability of maize (Zea mays L.) in cadmium contaminated soils

Abstract: Heavy metals (HMs) especially cadmium (Cd) absorbed by the roots of crop plants like maize have emerged as one of the most serious threats by causing stunted plant growth along with disturbing the photosynthetic machinery and nutrient homeostasis process. A trial was conducted for inducing Cd stress tolerance in maize by exogenous application of silicon nanoparticles (SiNPs) using five doses of SiNPs (0, 100, 200, 300, and 400 ppm) and three levels of Cd (0, 15, and 30 ppm) for maize hybrid (SF-9515). The response variables included morphological traits and biochemical parameters of maize. The results indicated that Cd level of 30 ppm remained the most drastic for maize plants by recording the minimum traits such as shoot length (39.35 cm), shoot fresh weight (9.52 g) and shoot dry weight (3.20 g), leaf pigments such as chlorophyll a (0.55 mg/g FW), chlorophyll b (0.27 mg/g FW), total contents (0.84 mg/g FW), and carotenoid contents (0.19 µg/g FW). Additionally, the same Cd level disrupted biochemical traits such as TSP (4.85 mg/g FW), TP (252.94 nmol/g FW), TSAA (18.92 µmol g-1 FW), TSS (0.85 mg/g FW), and antioxidant activities such as POD (99.39 min-1 g-1 FW), CAT (81.58 min-1 g-1 FW), APX (2.04 min-1 g-1 FW), and SOD (172.79 min-1 g-1 FW). However, a higher level of Cd resulted in greater root length (87.63 cm), root fresh weight (16.43 g), and root dry weight (6.14 g) along with higher Cd concentration in the root (2.52 µg/g-1) and shoot (0.48 µg/g-1). The silicon nanoparticles (Si NPs) treatment significantly increased all measured attributes of maize. The highest value was noted of all the parameters such as chlorophyll a (0.91 mg/g FW), chlorophyll b (0.57 mg/g FW), total chlorophyll contents (1.48 mg/g FW), total carotenoid contents (0.40 µg/g FW), TSP (6.12 mg/g FW), TP (384.56 nmol/g FW), TSAA (24.64 µmol g-1 FW), TSS (1.87 mg/g FW), POD (166.10 min-1 g-1 FW), CAT (149.54 min-1 g-1 FW), APX (3.49 min-1 g-1 FW), and SOD (225.57 min-1 g-1 FW). Based on recorded findings, it might be inferred that higher levels of Cd tend to drastically reduce morpho-physiological traits of maize and foliage-applied silver nanoparticles hold the potential to ameliorate the adverse effect of Cd stress on maize.

Solar energy conversion by photosystem II: principles and structures

Abstract: Photosynthetic water oxidation by Photosystem II (PSII) is a fascinating process because it sustains life on Earth and serves as a blue print for scalable synthetic catalysts required for renewable energy applications. The biophysical, computational, and structural description of this process, which started more than 50 years ago, has made tremendous progress over the past two decades, with its high-resolution crystal structures being available not only of the dark-stable state of PSII, but of all the semi-stable reaction intermediates and even some transient states. Here, we summarize the current knowledge on PSII with emphasis on the basic principles that govern the conversion of light energy to chemical energy in PSII, as well as on the illustration of the molecular structures that enable these reactions. The important remaining questions regarding the mechanism of biological water oxidation are highlighted, and one possible pathway for this fundamental reaction is described at a molecular level.

Quantification of Evapotranspiration by Calculations and Measurements Using a Lysimeter

Abstract: Evapotranspiration is one of the key elements of water balance in nature. It significantly influences the water supply in the unsaturated zone of a soil profile. The unsaturated zone is a water source for the biosphere. The aim of this study is to measure, calculate and analyze the course of actual evapotranspiration, precipitation and dew totals as well as the totals of water flows at the lower boundary of unsaturated zone and the change in water content in specified soil volume. The measurements are used for verifying the results of numerical simulation. The methods used in the study were chosen based on the hypothesis that dynamics of water supply changes in the unsaturated zone is the result of the interactions between atmosphere, soil and plant cover. The elements of water balance were quantified by the methods of water balance, lysimeter measurements and numerical simulation on the model HYDRUS-1D, version 4. The abovementioned parameters were quantified for the East Slovakian Lowland, with an hourly time step during the years 2017, 2018 and 2020. The measurements have shown that evapotranspiration exceeded precipitation during all monitored periods, specifically by 22% in 2017, by 14% in 2019, and by 10% in 2020. The deficit was compensated for by capillary inflow from the groundwater level and the water supply in the unsaturated zone. A verification by measurement has shown that numerical simulation is imprecise in relation to the quantification of water flows at the lower boundary of the unsaturated zone. This inaccuracy is manifested in the higher value of the actual evapotranspiration, which is on average exceeded by 11%. The performance of the mathematical model is assessed as satisfactory for the analysis of the soil water regime.

Efficacy of priming wheat (Triticum aestivum) seeds with a benzothiazine derivative to improve drought stress tolerance.

Abstract: We evaluated the effects of different concentrations (0.05 and 0.15mM) of a benzothiazine (BTh) derivative on wheat (Triticum aestivum L.) in normal (100% field water capacity, FWC) and drought (60% FWC) conditions. Various morphological and physiological characteristics, and the uptake of osmo-protectants and nutrients were measured under the two FWC conditions. Results show that the drought conditions significantly reduced plant growth, affected plant composition, reduced the concentrations of photosynthetic pigments and affected gaseous exchange attributes, stomatal behaviour, and uptake fluxes of essential nutrients, while increasing the contents of different osmo-protectants and enzymatic and non-enzymatic antioxidants to decrease the production of reactive oxygen species (ROS) within the cells/tissues. However, seed priming with BTh reduced water stress conditions by increasing plant growth and biomass, photosynthetic pigments, stomatal behaviour, different gaseous exchange attributes, and uptake fluxes of essential nutrients compared with unprimed plants. In addition, the plant has a strong antioxidant defense system, which further increased its activities under BTh derivative treatments, to scavenge ROS production and maintain cell turgor under water stress conditions. In conclusion, drought stress-induced oxidative stress and altered the growth of T. aestivum, whereas seed priming increased plant growth and antioxidant production by improving the plant tolerance to drought. We suggest that seed priming with a BTh derivative as an effective priming technique in T. aestivum for reducing drought stress tends to benefit a grower in terms of better growth to fulfil the market demand for food cereals.

Effects of Zinc Oxide and Silicon Dioxide Nanoparticles on Physiological, Yield, and Water Use Efficiency Traits of Potato Grown under Water Deficit

Abstract: Water deficit is a major challenge for sustainable global food security, especially, in arid and semi-arid regions. Nanotechnology is regarded as an effective tool for managing a wide range of environmental stresses by providing novel and practical solutions. A field experiment was conducted to assess the effects of zinc oxide nanoparticles ‘ZnO NPs’ (0, 50, 100 ppm) and silicon dioxide nanoparticles ‘SiO2 NPs’ (0, 25, 50 ppm) as an exogenous application on the physiological indices, total yield and water use efficiency (WUE) of potato under water deficit conditions (50%, 75%, and 100% of crop evapotranspiration (ETc) water requirements). Water deficit significantly decreased most physiological indices and yield traits of potato, but increased proline content and WUE. In contrast, exogenous application of ZnO NPs and SiO2 NPs to plants grown under different water deficit treatments resulted in an increase in leaf gas exchange, leaves relative water contents (LRWC), photosynthetic pigments, and leaf green index. Under different water deficit treatments, the highest total yield and harvest index traits were obtained from plants treated with ZnO-NPs-100 ppm followed by 50 ppm of ZnO and SiO2 NPs, respectively. The highest WUE was recorded when the potato plants were irrigated with 50% ETc and exogenous treated with 100 ppm of ZnO NPs compared with fully irrigated plants. In conclusion, the exogenous application of ZnO NPs (100 ppm) can significantly mitigate the water deficit stress and improve the physiological, yield, and WUE of potato grown in arid regions under water deficit conditions.

Photosynthetic microbial fuel cell for bioenergy and valuable production: A review of circular bio-economy approach

Abstract: Photosynthetic microbial fuel cells (PMFCs) are environmentally friendly fuel cells employed to produce renewable bioelectricity. These fuel cells require light to support their operation and are efficient to achieve high-power output. Depending upon the type of organism, they can be assisted by photosynthetic cell machinery in plants, bacteria, and algae. Algae assisted PMFCs are advantageous as they grow rapidly, require less space, produce free nascent oxygen and value-added products including bioelectricity. In this regard, this review elucidates the application and advantages of algae assisted PMFC over other PMFCs and their utility for recovery of bioelectricity and value-added products like polyunsaturated fatty acids, carotenoids, lutein, carbohydrates, proteins, polyhydroxyalkanoates, etc. Furthermore, the potential of generated bioelectricity and simultaneous resource recovery employing PMFCs are highlighted due to their low cost. Thus, this review can be a rapid guidebook for budding researchers in the field of PMFC's and possibly expedite the economical commercialization of PMFCs.

The battle of crops against drought: Genetic dissection and improvement.

Abstract: With ongoing global climate change, water scarcity-induced drought stress remains a major threat to agricultural productivity. Plants undergo a series of physiological and morphological changes to cope with drought stress, including stomatal closure to reduce transpiration and changes in root architecture to optimize water uptake. Combined phenotypic and multi-omics studies have recently identified a number of drought-related genetic resources in different crop species. The functional dissection of these genes using molecular techniques has enriched our understanding of drought responses in crops and has provided genetic targets for enhancing resistance to drought. Here, we review recent advances in the cloning and functional analysis of drought resistance genes and the development of technologies to mitigate the threat of drought to crop production. This article is protected by copyright. All rights reserved.

H2O2 alleviates salt stress effects on photochemical efficiency and photosynthetic pigments of cotton genotypes

Abstract: ABSTRACT The objective of this study was to evaluate the quantum yield and concentrations of photosynthetic pigments of naturally colored cotton genotypes under irrigation with waters of different electrical conductivities and foliar applications of hydrogen peroxide. The design used was randomized blocks in a 4 × 3 × 2 factorial arrangement, corresponding to four concentrations of hydrogen peroxide - H2O2 (0, 25, 50 and 75 μM), three genotypes of colored fiber cotton (‘BRS Rubi’, ‘BRS Topázio’ and ‘BRS Verde’) and two values of electrical conductivity of water (0.8 and 5.3 dS m-1), with three replicates. Irrigation with water of 5.3 dS m-1 reduces the chlorophyll a, chlorophyll b and total chlorophyll concentrations of ‘BRS Rubi’ cotton. The concentrations of photosynthetic pigments, maximum fluorescence, variable fluorescence and quantum efficiency of photosystem II of ‘BRS Rubi’ cotton increased under irrigation with 0.8 dS m-1 water and foliar application of 50 μM of hydrogen peroxide. Water of 5.3 dS m-1 and foliar applications of 75 μM of hydrogen peroxide reduce the concentrations of photosynthetic pigments, but did not cause damage to the efficiency of photosystem II of the colored cotton genotypes.

Silicon nanoparticles (SiNPs) restore photosynthesis and essential oil content by upgrading enzymatic antioxidant metabolism in lemongrass (Cymbopogon flexuosus) under salt stress

Abstract: Lemongrass (Cymbopogon flexuosus) has great relevance considering the substantial commercial potential of its essential oil. Nevertheless, the increasing soil salinity poses an imminent threat to lemongrass cultivation given its moderate salt-sensitivity. For this, we used silicon nanoparticles (SiNPs) to stimulate salt tolerance in lemongrass considering SiNPs special relevance to stress settings. Five foliar sprays of SiNPs 150 mg L-1 were applied weekly to NaCl 160 and 240 mM-stressed plants. The data indicated that SiNPs minimised oxidative stress markers (lipid peroxidation, H2O2 content) while triggering a general activation of growth, photosynthetic performance, enzymatic antioxidant system including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), and osmolyte proline (PRO). SiNPs amplified stomatal conductance and photosynthetic CO2 assimilation rate by about 24% and 21% in NaCl 160 mM-stressed plants. Associated benefits contributed to pronounced plant phenotype over their stressed counterparts, as we found. Foliar SiNPs sprays assuaged plant height by 30% and 64%, dry weight by 31% and 59%, and leaf area by 31% and 50% under NaCl 160 and 240 mM concentrations, respectively. SiNPs relieved enzymatic antioxidants (SOD, CAT, POD) and osmolyte (PRO) in lemongrass plants stressed with NaCl 160 mM (9%, 11%, 9%, and 12%, respectively) and NaCl 240 mM (13%, 18%, 15%, and 23%, respectively). The same treatment supported the oil biosynthesis improving essential oil content by 22% and 44% during 160 and 240 mM salt stress, respectively. We found SiNPs can completely overcome NaCl 160 mM stress while significantly palliating NaCl 240 mM stress. Thus, we propose that SiNPs can be a useful biotechnological tool to palliate salinity stress in lemongrass and related crops.

Enhancement of Morphological and Physiological Performance of Zea mays L. under Saline Stress Using ZnO Nanoparticles and 24-Epibrassinolide Seed Priming

Abstract: Salinity is one of the most devastating environmental factors limiting crop productivity worldwide. Therefore, our study investigates the effect of seed priming with zinc oxide nanoparticles (ZnO NPs: 0, 50, and 100 mg L−1), 24-epibrassinolide (EBL: 0.0, 0.2, and 0.4 µM), and their combined treatments on maize (Zea mays L.) grown with different levels of saline stress (i.e., control, 5, 10 dS m−1) under semi-controlled conditions. Higher saline stress (10 dS m−1) negatively influenced the growth traits, physiological attributes, and elemental (i.e., Zn and K) uptake for both roots and shoots of maize, whereas it increased Na+ accumulation and Na+/K+ ratio in comparison to other treatments. However, seed priming with ZnO NPs and EBL as well as their combinations showed amelioration of the detrimental effects of saline stress on the growth and physiological and biochemical performance of maize. In general, seed priming with combined treatments of ZnO NPs and EBL were significantly more effective than either ZnO NPs or EBL as individual treatments. A combination of 100 mg L−1 ZnO NPS + 0.2 µM EBL resulted in the highest values of root length, root surface area, stem diameter, relative leaf water contents, total chlorophyll, net rate of photosynthesis, zinc accumulation, and K+ uptake, while it resulted in the lowest Na+ and Na+/K+ ratio, especially under the highest saline-stress treatment. Thus, we concluded that seed priming with combined ZnO NPs and EBL can effectively mitigate the saline-stress-mediated decline in the morphological, physiological, and biochemical traits of maize.

Carbon isotope fractionation by an ancestral rubisco suggests biological proxies for CO2 through geologic time should be re-evaluated

Abstract: The history of Earth’s carbon cycle reflects trends in atmospheric composition convolved with the evolution of photosynthesis. Fortunately, key parts of the carbon cycle have been recorded in the carbon isotope ratios of sedimentary rocks. The dominant model used to interpret this record as a proxy for ancient atmospheric CO2 is based on carbon isotope fractionations of modern photoautotrophs, and longstanding questions remain about how their evolution might have impacted the record. We tested the intersection of environment and evolution by measuring both biomass (εp) and enzymatic (εRubisco) carbon isotope fractionations of a cyanobacterial strain (Synechococcus elongatus PCC 7942) solely expressing a putative ancestral Form 1B rubisco dating to ≫1 Ga. This strain, nicknamed ANC, grows in ambient pCO2 and displays larger εp values than WT, despite having a much smaller εRubisco (17.23 ± 0.61‰ vs. 25.18 ± 0.31‰ respectively). Measuring both enzymatic and biomass fractionation revealed a surprising result—ANC εp exceeded ANC εRubisco in all conditions tested, contradicting prevailing models of cyanobacterial carbon isotope fractionation. However, these models were corrected by accounting for cyanobacterial physiology, notably the CO2 concentrating mechanism (CCM). Our model suggested that additional fractionating processes like powered inorganic carbon uptake systems contribute to εp, and this effect is exacerbated in ANC. Understanding the evolution of rubisco and the CCM is therefore critical for interpreting the carbon isotope record. Large fluctuations in that record may reflect the evolving efficiency of carbon fixing metabolisms in addition to changes in atmospheric CO2. Significance Statement Earth scientists rely on chemical fossils like the carbon isotope record to derive ancient atmospheric CO2 concentrations, but interpretation of this record is calibrated using modern organisms. We tested this assumption by measuring the carbon isotope fractionation of a reconstructed ancestral rubisco enzyme (>1 billion years old) in vivo and in vitro. Our results contradicted prevailing models of carbon flow in Cyanobacteria, but our data could be rationalized if light-driven uptake of CO2 is taken into account. Our study showed that the carbon isotope record tracks both the evolution of photosynthesis physiology as well as changes in atmospheric CO2, highlighting the value of considering both evolution and physiology for comparative biological approaches to understanding Earth’s history.

Algal cell bionics as a step towards photosynthesis-independent hydrogen production

Abstract: The engineering and modulation of living micro-organisms is a key challenge in green bio-manufacturing for the development of sustainable and carbon-neutral energy technologies. Here, we develop a cellular bionic approach in which living algal cells are interfaced with an ultra-thin shell of a conductive polymer along with a calcium carbonate exoskeleton to produce a discrete cellular micro-niche capable of sustained photosynthetic and photosynthetic-independent hydrogen production. The surface-augmented algal cells induce oxygen depletion, conduct photo-induced extracellular electrons, and provide structural and chemical stability that collectively give rise to localized hypoxic conditions and concomitant hydrogenase activity under daylight in air. We show that assembly of the living cellular micro-niche opens a direct extracellular photoelectron pathway to hydrogenase resulting in photosynthesis-independent hydrogen evolution for 200 d. In addition, surface-conductive dead algal cells continue to produce hydrogen for up to 8 d due to their structural stability and retention of functional hydrogenases. Overall, the integration of artificial biological hydrogen production pathways and natural photosynthesis in surface-augmented algal cells provides a cellular bionic approach to enhanced green hydrogen production under environmentally benign conditions and could pave the way to new opportunities in sustainable energy production.

SlIAA9 Mutation Maintains Photosynthetic Capabilities under Heat-Stress Conditions

Abstract: Tomato is one of the most widely consumed horticultural products. However, tomato is very sensitive to changes in temperature. Daily average temperatures above 32 °C severely reduced tomato plant growth, development, and productivity. Therefore, climate change-induced global warming is a major threat to future tomato production. Good photosynthetic capability under heat stress conditions is known to be a major sign of heat tolerance. Tomato INDOLE-ACETIC-ACID (SlIAA9) is a transcriptional repressor in auxin signaling. SlIAA9 mutation caused heightened endogenous auxin response and biosynthesis within plant tissues. In this study, we studied the photosynthetic capability of iaa9-3 and iaa9-5 mutants under heat-stress conditions. We discovered that both iaa9-3 and iaa9-5 could maintain their photosynthetic capability after 14 days of heat treatment (>40 °C), differing from Wild Type-Micro-Tom (WT-MT) tomato. Both iaa9 mutants had higher net photosynthetic rate, stomatal conductance, leaf total chlorophyll, leaf carotenoids, Fv/Fm value, and lower leaf MDA than WT-MT. These results suggested that the SlIAA9 mutation benefits plant adaptation to heat stress.

Silicic and Ascorbic Acid Induced Modulations in Photosynthetic, Mineral Uptake, and Yield Attributes of Mung Bean (Vigna radiata L. Wilczek) under Ozone Stress

Abstract: Most of the world’s crop production and plant growth are anticipated to be seriously threatened by the increasing tropospheric ozone (O3) levels. The current study demonstrates how different mung bean genotypes reacted to the elevated level of O3 in the presence of exogenous ascorbic and silicic acid treatments. It is the first report to outline the potential protective effects of ascorbic and silicic acid applications against O3 toxicity in 12 mung bean {Vigna radiata (L.) Wilken} varieties. Under controlled circumstances, the present investigation was conducted in a glass house. There were four different treatments used: control (ambient O3 concentration of 40–45 ppb), elevated O3 (120 ppb), elevated O3 with silicic acid (0.1 mM), and elevated O3 with ascorbic acid (10 mM). Three varieties, viz. NM 20-21, NM 2006, and NM 2016, showcased tolerance to O3 toxicity. Our findings showed that ascorbic and silicic acid applications gradually increased yield characteristics such as seed yield, harvest index, days to maturity, and characteristics related to gas exchange such as transpiration rate, stomatal conductance, net photosynthetic activity, and water-use efficiency. Compared to the control, applying both growth regulators enhanced the mineral uptake across all treatments. Based on the findings of the current study, it is concluded that the subject mung bean genotypes responded to silicic acid treatment more efficiently than ascorbic acid to mitigate the harmful effects of O3 stress.

Is it realistic to use microbial photosynthesis to produce electricity directly?

Abstract: It is possible to generate small amounts of electrical power directly from photosynthetic microorganisms—arguably the greenest of green energy. But will it have useful applications, and what are the hurdles if so?

Core cellular and tissue specific mechanisms enable desiccation tolerance in Craterostigma.

Abstract: Resurrection plants can survive prolonged life without water (anhydrobiosis) in regions with seasonal drying. This desiccation tolerance requires the coordination of numerous cellular processes across space and time, and individual plant tissues face unique constraints related to their function. Here, we analyzed the complex, octoploid genome of the model resurrection plant Craterostigma (C. plantagineum) and surveyed spatial and temporal expression dynamics to identify genetic elements underlying desiccation tolerance. Homeologous genes within the Craterostigma genome have divergent expression profiles, suggesting the subgenomes contribute differently to desiccation tolerance traits. The Craterostigma genome contains almost 200 tandemly duplicated early light induced proteins (ELIPs), a hallmark trait of desiccation tolerance, with massive upregulation under water deficit. We identified a core network of desiccation responsive genes across all tissues but observed almost entirely unique expression dynamics in each tissue during recovery. Roots and leaves have differential responses related to light and photoprotection, autophagy, and nutrient transport, reflecting their divergent functions. Our findings highlight a universal set of likely ancestral desiccation tolerance mechanisms to protect cellular macromolecules under anhydrobiosis, with secondary adaptations related to tissue function.

Strigolactone-Mediated Mitigation of Negative Effects of Salinity Stress in Solanum lycopersicum through Reducing the Oxidative Damage

Abstract: Soil salinity is one of the main barriers to increasing global food production as it reduces crop growth and productivity. While irrigated lands in arid climates (about 20% of total affected) are more prone to salinization, many other natural and anthropogenic factors contribute to an increase in salinity in arable lands that currently affects over 100 countries and more than one billion ha. Management of agro-ecosystems at every level, including soil, water, and the plant itself, is important in mitigating the effects of salinity. Plant hormones control cellular metabolism, and mediate plant defense response mechanisms against abiotic and biotic stresses. Foliar fertigation with plant growth regulators has been shown to improve growth and metabolism under stress conditions. Strigolactones (SLs) have emerged as a group of novel phytohormones with several functions in plant interactions with microorganisms, plant metabolism, development, and in responding to many environmental cues. The present research addressed SL (GR24) effects on growth, photosynthetic parameters, and oxidative stress in Solanum lycopersicum under salinity stress. Growth indices, photosynthesis and related attributes, antioxidant enzyme activity, and malondialdehyde (a product of lipid peroxidation) and hydrogen peroxide concentrations were compared in unstressed and salt-stressed (NaCl; 150 mM) S. lycopersicum seedlings untreated or treated with GR24 (2 µM). Improved antioxidant enzyme activity, proline (8%) and protein (14%) contents, and photosynthetic (33%) and transpiration (34%) parameters under GR24 treatment result in a significant increase in plant growth parameters, viz., shoot length (29%), root length (21%), shoot fresh weight (31%), root fresh weight (23%), shoot dry weight (26%), and root dry weight (19%). Increased chlorophyll index (14%) and stomatal conductance (16%) in GR24-applied plants under salinity stress results in improved growth and photosynthetic efficiency of S. lycopersicum. Our results add to the existing knowledge of the relatively new function of SLs in mitigating abiotic stress, particularly that of salinity stress in crop plants.

Light-independent regulation of algal photoprotection by CO2 availability

Abstract: Abstract Photosynthetic algae have evolved mechanisms to cope with suboptimal light and CO 2 conditions. When light energy exceeds CO 2 fixation capacity, Chlamydomonas reinhardtii activates photoprotection, mediated by LHCSR1/3 and PSBS, and the CO 2 Concentrating Mechanism (CCM). How light and CO 2 signals converge to regulate these processes remains unclear. Here, we show that excess light activates photoprotection- and CCM-related genes by altering intracellular CO 2 concentrations and that depletion of CO 2 drives these responses, even in total darkness. High CO 2 levels, derived from respiration or impaired photosynthetic fixation, repress LHCSR3 /CCM genes while stabilizing the LHCSR1 protein. Finally, we show that the CCM regulator CIA5 also regulates photoprotection, controlling LHCSR3 and PSBS transcript accumulation while inhibiting LHCSR1 protein accumulation. This work has allowed us to dissect the effect of CO 2 and light on CCM and photoprotection, demonstrating that light often indirectly affects these processes by impacting intracellular CO 2 levels.

Chlamydomonas mutants lacking chloroplast TRIOSE PHOSPHATE TRANSPORTER3 are metabolically compromised and light-sensitive.

Abstract: Modulation of photoassimilate export from the chloroplast is essential for controlling the distribution of fixed carbon in the cell and maintaining optimum photosynthetic rates. In this study we identified chloroplast TRIOSE PHOSPHATE/PHOSPHATE TRANSLOCATOR2 (CreTPT2) and CreTPT3 in the green alga Chlamydomonas (Chlamydomonas reinhardtii), which exhibit similar substrate specificities but whose encoding genes are differentially expressed over the diurnal cycle. We focused mostly on CreTPT3 because of its high level of expression and the severe phenotype exhibited by tpt3 relative to tpt2 mutants. Null mutants for CreTPT3 had a pleiotropic phenotype that affected growth, photosynthetic activities, metabolite profiles, carbon partitioning, and organelle-specific accumulation of H2O2. These analyses demonstrated that CreTPT3 is a dominant conduit on the chloroplast envelope for the transport of photoassimilates. In addition, CreTPT3 can serve as a safety valve that moves excess reductant out of the chloroplast and appears to be essential for preventing cells from experiencing oxidative stress and accumulating reactive oxygen species, even under low/moderate light intensities. Finally, our studies indicate subfunctionalization of the CreTPT transporters and suggest that there are differences in managing the export of photoassimilates from the chloroplasts of Chlamydomonas and vascular plants.

Exogenous Calcium Reinforces Photosynthetic Pigment Content and Osmolyte, Enzymatic, and Non-Enzymatic Antioxidants Abundance and Alleviates Salt Stress in Bread Wheat

Abstract: One of the main environmental stresses that hinder crop development as well as yield is salt stress, while the use of signal molecules such as calcium (Ca) has a substantial impact on reducing the detrimental effects of salt on different crop types. Therefore, a factorial pot experiment in a completely randomized design was conducted to examine the beneficial role of Ca (0, 2.5, and 5 mM) in promoting the physiological, biochemical, and growth traits of the wheat plant under three salt conditions viz. 0, 30, and 60 mM NaCl. Foliar application of Ca increased the growth of salt-stressed wheat plants through increasing photosynthetic pigments, IAA, proline, and total soluble sugars contents and improving antioxidant enzymes in addition to non-enzymatic antioxidants glutathione, phenol and flavonoids, β-carotene, and lycopene contents, thus causing decreases in the over-accumulation of free radicals (ROS). The application of Ca increased the activity of antioxidant enzymes in wheat plants such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), which scavenge reactive oxygen species (ROS) and relieved salt stress. An additional salt tolerance mechanism by Ca increases the non-antioxidant activity of plants by accumulating osmolytes such as free amino acids, proline, and total soluble sugar, which maintain the osmotic adjustment of plants under salinity stress. Exogenous Ca application is a successful method for increasing wheat plants’ ability to withstand salt stress, and it has a considerable impact on the growth of wheat under salt stress.