Plant Photosynthetic Efficiency Research Articles

Foliar application of phosphoric acid mitigates oxidative stress induced by herbicides in soybean, maize, and cotton crops

Foliar fertilization presents a potential solution in alleviating oxidative stress triggered by herbicide exposure. Enhancing our comprehension of the interplay between foliar fertilization, oxidative stress, and herbicide application is pivotal for enhancing crop yield. Carfentrazone, a herbicide, prompts the buildup of reactive oxygen species, leading to detrimental effects on cell membranes and the manifestation of chlorotic spots on leaves. This research administered carfentrazone-ethyl to soybean, maize, and cotton to induce stress. The herbicide application was followed by foliar application of phosphorus (H3PO4) to evaluate its effect on phytotoxicity recovery. The evaluations included leaf nutritional analyses, gas exchange measurements (photosynthesis, stomatal conductance, substomatal CO2 concentration, and Leaf transpiration), photosynthetic pigments (chlorophylls and carotenoids), oxidative stress indicators (MDA, H2O2, SOD, CAT and APX), and productivity parameters (height, number of branches, pods, grains, 100-grain weight, and yield), in addition to the activity of the enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), which is crucial for carbon fixation and the photosynthetic efficiency of plants. Phosphorus (P) improved chlorophyll levels by up to 28.8% and Rubisco activity by up to 24.8%, leading to increases in the net photosynthetic rate by up to 40.2%, stomatal conductance, water use efficiency, and carboxylation. In addition, foliar P fertilization enhanced antioxidant metabolism, with reductions in markers of oxidative stress (H2O2 and MDA) by up to 39.1%. Collectively, these effects of foliar P fertilization increased the productivity of the three crops by up to 55.9%, indicating that foliar supplementation with P is an effective strategy to mitigate phytotoxicity symptoms.. In soybeans at the V4 and V6 stages, it has been shown to improve net photosynthesis, enhance Rubisco activity, and reduce oxidative stress. In maize, the V4 stage proved to be more effective, increasing Rubisco activity and improving productivity. For cotton, the B1 stage was more beneficial, resulting in increased boll weight and fiber yield. This study introduces an innovative approach of foliar P-supplementation to mitigate herbicide-induced oxidative stress in crops. This management strategy enhances crop resilience, improves yield stability, and provides a sustainable solution to a critical challenge in modern agriculture.

Screening of environmental stimuli for the positive regulation of stomatal aperture in centipedegrass

Grasslands, the largest carbon pool in China, possess enormous potential for carbon sequestration. Increasing the stomatal aperture to increase the CO2 absorption capacity is a potential method to improve plant photosynthetic efficiency and ultimately enhance the carbon sequestration capacity of grass plants. Research on stomatal aperture regulation has focused mostly on Arabidopsis or crops, while research on grass plants in these areas is scarce, which seriously restricts the implementation of this grassland carbon sequestration strategy. Here, a widely used ecological grass, centipedegrass, was used as the experimental material. First, a convenient method for observing the stomatal aperture was developed. The leaves were floated in a potassium ion-containing open solution (67 mM KCl, pH 6.0) with the adaxial surface rather than the abaxial surface in contact with the solution and were cultivated under light for 1.5 h. Then, nail polish was applied on the adaxial surface, and a large number of open stomata were imprinted. Second, with the help of this improved method, the concentration‒response characteristics of the stomatal aperture to eleven environmental stimuli were tested. The stomatal aperture is dependent on these environmental stimuli in a concentration-dependent manner. The addition of 100 μM brassinolide led to the maximal stomatal aperture. This study provided a technical basis for manipulating stomatal opening to increase the carbon sequestration capacity of centipedegrass.

Study on the Mechanism of Exogenous 5-Aminolevulinic Acid (ALA) in Regulating the Photosynthetic Efficiency of Pear Leaves

To provide a theoretical basis for the application of ALA in pear production, the effects of exogenous 5-aminolevulinic acid (ALA) treatment on leaf photosynthetic gas exchange parameters, chlorophyll fast fluorescence properties, and relative expression of the related genes were investigated using pear (Pyrus pyrifolia Nakai cv. ‘Whasan’) as a material in the study. The results show that exogenous ALA treatment improved the photosynthetic gas exchange parameters of pear leaves, upregulated the expression of multiple key genes which are related to ALA biosynthesis, metabolism, and transformation into chlorophylls. GUS staining in tobacco leaves showed that exogenous ALA activated the promoter activity of PypHEMA and PypCHLH genes, implying that the synthesis of endogenous ALA and chlorophylls was promoted by exogenous ALA. Furthermore, ALA promoted the expression of the genes encoding photosystem II (PSII) reaction center proteins, such as core protein D1, inner light-harvesting pigment proteins CP43 and CP47, and cytochrome b559. This led to increased PSII reaction center activity. In addition, ALA alleviated the donor side oxygen-evolving complex inhibition and reduced the closure rate on the receptor side, allowing for increased photochemical electron transfer and reduced heat dissipation while improving the photosynthetic performance index PIabs and PItotal. The findings of this study contribute to a better understanding of ALA’s promotion of plant photosynthetic efficiency, providing valuable insights for further research and potential applications in pear production.

Structure and assembly of the α-carboxysome in the marine cyanobacterium Prochlorococcus.

Carboxysomes are bacterial microcompartments that encapsulate the enzymes RuBisCO and carbonic anhydrase in a proteinaceous shell to enhance the efficiency of photosynthetic carbon fixation. The self-assembly principles of the intact carboxysome remain elusive. Here we purified α-carboxysomes from Prochlorococcus and examined their intact structures using single-particle cryo-electron microscopy to solve the basic principles of their shell construction and internal RuBisCO organization. The 4.2 Å icosahedral-like shell structure reveals 24 CsoS1 hexamers on each facet and one CsoS4A pentamer at each vertex. RuBisCOs are organized into three concentric layers within the shell, consisting of 72, 32 and up to 4 RuBisCOs at the outer, middle and inner layers, respectively. We uniquely show how full-length and shorter forms of the scaffolding protein CsoS2 bind to the inner surface of the shell via repetitive motifs in the middle and C-terminal regions. Combined with previous reports, we propose a concomitant 'outside-in' assembly principle of α-carboxysomes: the inner surface of the self-assembled shell is reinforced by the middle and C-terminal motifs of the scaffolding protein, while the free N-terminal motifs cluster to recruit RuBisCO in concentric, three-layered spherical arrangements. These new insights into the coordinated assembly of α-carboxysomes may guide the rational design and repurposing of carboxysome structures for improving plant photosynthetic efficiency.

Host RNAi-mediated silencing of Fusarium oxysporum f. sp. lycopersici specific-fasciclin-like protein genes provides improved resistance to Fusarium wilt in Solanum lycopersicum.

Tomato transgenics expressing dsRNA against FoFLPs act as biofungicides and result in enhanced disease resistance upon Fol infection, by downregulating the endogenous gene expression levels of FoFLPs within Fol. Fusarium oxysporum f. sp. lycopersici (Fol) hijacks plant immunity by colonizing within the host and further instigating secondary infection causing vascular wilt disease in tomato that leads to significant yield loss. Here, RNA interference (RNAi) technology was used to determine its potential in enduring resistance against Fusarium wilt in tomato. To gain resistance against Fol infection, host-induced gene silencing (HIGS) of Fol-specific genes encoding for fasciclin-like proteins (FoFLPs) was done by generating tomato transgenics harbouring FoFLP1, FoFLP4 and FoFLP5 RNAi constructs confirmed by southern hybridizations. These tomato transgenics were screened for stable siRNA production in T0 and T1 lines using northern hybridizations. This confirmed stable dsRNAhp expression in tomato transgenics and suggested durable trait heritability in the subsequent progenies. FoFLP-specific siRNAs producing T1 tomato progenies were further selected to ascertain its disease resistance ability using seedling infection assays. We observed a significant reduction in FoFLP1, FoFLP4 and FoFLP5 transcript levels in Fol, upon infecting their respective RNAi tomato transgenic lines. Moreover, tomato transgenic lines, expressing intended siRNA molecules in the T1 generation, exhibit delayed disease onset with improved resistance. Furthermore, reduced fungal colonization was observed in the roots of Fol-infected T1 tomato progenies, without altering the plant photosynthetic efficiency of transgenic plants. These results substantiate the cross-kingdom dsRNA or siRNA delivery from transgenic tomato to Fol, leading to enhanced resistance against Fusarium wilt disease. The results also demonstrated that HIGS is a successful approach in rendering resistance to Fol infection in tomato plants.

Diversity and Traits of Multiple Biotic Stressors Elicit Differential Defense Responses in Legumes

In agroecosystems, plants frequently confront multiple biotic stressors, including herbivores and pathogens. The nature of these interactions plays a crucial role in mediating the activation of plant defense mechanisms. However, induction of plant chemical defenses has been more well studied than the induction of physical defenses. Here, we assessed the physical and chemical defense responses of pea (Pisum sativum) plants after exposure to three stressors: a vector herbivore (pea aphid, Acrythosiphon pisum), a non-vector herbivore (pea leaf weevil, Sitona lineatus), and a virus (Pea enation mosaic virus, PEMV). We used various histochemical staining techniques show that viruliferous A. pisum (transmitting PEMV) strongly induced callose deposition (aniline blue staining) and antioxidant-mediated defenses (DAB and NBT staining) in peas, primarily through accumulating reactive oxygen species (ROS). High-throughput phenotyping showed that viruliferous aphids reduced plant photosynthetic efficiency, but plants infected with PEMV had increased cell death (trypan blue staining). However, herbivory by aphids and weevils did not strongly induce defenses in peas, even though weevil feeding significantly reduced pea leaf area. These results show that not all herbivores induce strong defensive responses, and plant responses to vector species depends on their virus infection status. More broadly, our results indicate that variable stressors differentially regulate various plant responses through intricate chemical and physical defense pathways.

Impact of phosphorus omission fertilizer on growth, nutritional status, biochemical and physiological parameters in a Pinus taeda L. plantation

Low availability of phosphorus (P) in the soil is one of the factors limiting the productivity of Pinus taeda plantations. Phosphate fertilizer application in Pinus shows divergence in growth responses. Thus, understanding the response of plant photosynthetic efficiency and growth in relation to phosphate fertilizer application can serve as a basis to guide management practices in Pinus taeda plantations. The study aimed to evaluate the impact of P omission fertilizer on growth parameters, nutritional, biochemical, and physiological status of a Pinus taeda L. plantation. The experiment was conducted on a Pinus taeda plantation subjected to P fertilization: Control - without addition of N, P and K; P–fertilized - with addition of N, P and K; and P–omission - addition of N and K, and P omission fertilizer. The parameters height, stem and canopy diameter and productivity factor, P concentration in needles, soil available P, electron transport rate (ETRm), maximum quantum yield of PSII (Fv/Fm), initial (Fo) and maximum (Fm) fluorescence, chlorophyll a, b and total, carotenoids, superoxide dismutase (SOD) and peroxidase (POD), hydrogen peroxide (H2O2), lipid peroxidation (TBARS), and acid phosphatase activity, were evaluated. P fertilized application increased soil available P, providing largest P uptake by roots and P concentration in needles. The increase in available soil P contributed to elevate photosynthetic parameters, such as ETRm, Fv/Fm, chlorophyll a, b and total, and carotenoids. These factors contributed to increase C assimilation, height, stem and canopy diameter and productivity factor parameters. On the other hand, the P–omission and control conditioned the growth of Pinus taeda under stress, elevating the values of Fo, Fm, SOD and POD, which reduced plant development.

Assessment of Combined Reflectance, Transmittance, and Absorbance Hyperspectral Sensors for Prediction of Chlorophyll a Fluorescence Parameters

Photosynthesis is a key process in plant physiology. Understanding its mechanisms is crucial for optimizing crop yields and for environmental monitoring across a diverse range of plants. In this study, we employed reflectance, transmittance, and absorbance hyperspectral sensors and utilized multivariate statistical techniques to improve the predictive models for chlorophyll a fluorescence (ChlF) parameters in Hibiscus and Geranium model plants. Our objective was to identify spectral bands within hyperspectral data that correlate with ChlF indicators using high-resolution data spanning the electromagnetic spectrum from ultraviolet to shortwave infrared (UV–VIS–NIR–SWIR). Utilizing the hyperspectral vegetation indices (HVIs) tool to align importance projection for wavelength preselection and select the most responsive wavelength by variable importance projection (VIP), we optimized partial least squares regression (PLSR) models to enhance predictive accuracy. Our findings revealed a strong relationship between hyperspectral sensor data and ChlF parameters. Employing principal component analysis, kappa coefficients (k), and accuracy (Acc) evaluations, we achieved values exceeding 86% of the predicted ChlF parameters for both Hibiscus and Geranium plants. Regression models for parameters such as Ψ(EO), ϕ(PO), ϕ(EO), ϕ(DO), δRo, ρRo, Kn, Kp, SFI(abs), PI(abs), and D.F. demonstrated model accuracies close to 0.84 for R2 and approximately 1.96 for RPD. The spectral regions linked with these parameters included blue, green, red, infrared, SWIR1, and SWIR2, emphasizing their relevance for noninvasive evaluations. This research demonstrates the ability of hyperspectral sensors to noninvasively predict chlorophyll a fluorescence (ChlF) parameters, which are essential for assessing photosynthetic efficiency in plants. Notably, hyperspectral absorbance data were more accurate in predicting JIP-test-based chlorophyll a kinetic parameters. In conclusion, this study underscores the potential of hyperspectral sensors for deepening our understanding of plant photosynthesis and monitoring plant health.

Long Exposure to Salt Stress in Jatropha curcas Leads to Stronger Damage to the Chloroplast Ultrastructure and Its Functionality Than the Stomatal Function

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

Phosphoribulokinase abundance is not limiting the Calvin-Benson-Bassham cycle in Chlamydomonas reinhardtii.

Improving photosynthetic efficiency in plants and microalgae is of utmost importance to support the growing world population and to enable the bioproduction of energy and chemicals. Limitations in photosynthetic light conversion efficiency can be directly attributed to kinetic bottlenecks within the Calvin-Benson-Bassham cycle (CBBC) responsible for carbon fixation. A better understanding of these bottlenecks in vivo is crucial to overcome these limiting factors through bio-engineering. The present study is focused on the analysis of phosphoribulokinase (PRK) in the unicellular green alga Chlamydomonas reinhardtii. We have characterized a PRK knock-out mutant strain and showed that in the absence of PRK, Chlamydomonas cannot grow photoautotrophically while functional complementation with a synthetic construct allowed restoration of photoautotrophy. Nevertheless, using standard genetic elements, the expression of PRK was limited to 40% of the reference level in complemented strains and could not restore normal growth in photoautotrophic conditions suggesting that the CBBC is limited. We were subsequently able to overcome this initial limitation by improving the design of the transcriptional unit expressing PRK using diverse combinations of DNA parts including PRK endogenous promoter and introns. This enabled us to obtain strains with PRK levels comparable to the reference strain and even overexpressing strains. A collection of strains with PRK levels between 16% and 250% of WT PRK levels was generated and characterized. Immunoblot and growth assays revealed that a PRK content of ≈86% is sufficient to fully restore photoautotrophic growth. This result suggests that PRK is present in moderate excess in Chlamydomonas. Consistently, the overexpression of PRK did not increase photosynthetic growth indicating that that the endogenous level of PRK in Chlamydomonas is not limiting the Calvin-Benson-Bassham cycle under optimal conditions.

Phosphorus and naphthalene acetic acid increased the seed yield by regulating carbon and nitrogen assimilation of flax.

To evaluate the impact of phosphorus (P) combined with exogenous NAA on flax yield, enhance flax P utilization efficiency and productivity, minimize resource inputs and mitigate negative environmental and human effects. Therefore, it is crucial to comprehend the physiological and biochemical responses of flax to P and naphthylacetic acid (NAA) in order to guide future agronomic management strategies for increasing seed yield. A randomized complete block design trial was conducted under semi-arid conditions in Northwest China, using a factorial split-plot to investigate the effects of three P (0, 67.5, and 135.0kg P2O5 ha-1) and three exogenous spray NAA levels (0, 20, and 40 mg NAA L-1) on sucrose phosphate synthase (SPS) and diphosphoribulose carboxylase (Rubisco) activities as well as nitrogen (N) and P accumulation and translocation in flax. Results indicated that the SPS and Rubisco activities, N and P accumulation at flowering and maturity along with assimilation and translocation post-flowering, fruiting branches per plant, tillers per plant, capsules per plant, and seed yield were 95, 105, 14, 27, 55, 15, 13, 110, 103, 82, 16, 61, 8, and 13% greater in the P treatments compared to those in the zero P treatment, respectively. Moreover, those characteristics were observed to be greater with exogenous spray NAA treatments compared to that no spray NAA treatment. Additionally, the maximum SPS and Rubisco activities, N and P accumulation, assimilation post-flowering and translocation, capsules per plant, and seed yield were achieved with the application of 67.5kg P2O5 ha-1 with 20 mg NAA L-1. Therefore, these findings demonstrate that the appropriate combination of P fertilizer and spray NAA is an effective agronomic management strategy for regulating carbon and nitrogen assimilation by maintaining photosynthetic efficiency in plants to increase flax productivity.

Effect of nano-calcium carbonate on morphology, antioxidant enzyme activity and photosynthetic parameters of wheat (Triticum aestivum L.) seedlings

To meet the human demand for crop productivity, there are several challenges that researchers are involved in the photosynthetic efficiency of plants may be one of them. Nanotechnology can improve agricultural productivity by affecting the photosynthetic activity of plants. However, no studies have yet shown that nano-calcium carbonate (NCC) can play a role in improving photosynthetic performance of plants. In order to explore the effects of NCC on wheat seedling morphology, antioxidant enzyme activities and photosynthetic parameters, wheat roots were exposed to different concentrations of NCC (0, 25, 50, 100, 200, 400 mg L−1) through hydroponic experiments. Different concentrations affected root length, root surface area, root diameter, root volume and plant dry biomass. Compared to the control (0 mg L−1 of NCC) application (CK), wheat with 200 mg L−1 of NCC application showed 54% and 58% increase in superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities, respectively. As for photosynthesis-related physiological indicators, compared with CK, 200 mg L−1 of NCC significantly enhanced chlorophyll a (38%), chlorophyll b (20%), carotenoid content (19%), Rubisco activity (3.02-fold), net photosynthetic rate (Pn, 56%), transpiration rate (Tr, 40%), and stomatal conductance (Gs, 71%). The PCR results showed that compared with CK, the psbA gene encoding the photosystem PSII reaction center D1 protein and the rbcL gene encoding the large subunit of Rubisco were up-regulated by 2.56- and 2.58-fold at 200 mg L−1 NCC treatment, and by 3.22- and 3.57-fold at 400 mg L−1 NCC treatment, respectively. Specifically, NCC has significant benefits on wheat seedling growth, and 200 mg L−1 is the optimal concentration. NCC enhanced photosynthetic performance of wheat by increasing antioxidant enzyme activity, photosynthetic pigment content, Rubisco activity, stomatal conductance and PSII reaction center activity.Graphical

Biochemical, pathological and molecular characterisation of Phomopsis vexans: A causative of leaf blight and fruit rot in brinjal

The pathogen Phomopsis vexans causes leaf blight, fruit rot, and damping off in brinjal plants, all of which are extremely detrimental. The pathogen affects host plant photosynthetic efficiency and fruit quantity and quality. An appreciation of the pathogenicity of P. vexans is essential for the effective control of infections in the field. Consequently, the goal of this study was to characterise P. vexans in terms of their biochemistry, molecular diversity, and pathogenicity. In terms of cellulase (97.7 U), catalase (12.2 U), and ascorbate peroxidase (147.3 U) activity, isolate PV1 performed best, followed by PV5 (CL-97.0 U, CAT-11.1 U and APX-144.4 U), and PV8 (CL-88.8 U, CAT-9.8 U and APX-141.9 U). In a greenhouse pathogenicity test, isolate PV1 had the highest incidence (97%) and severity (88.6%) of disease, whereas isolate PV6 showed the lowest incidence (57.2%) and severity (70%) of disease. The biochemical enzyme activity of P. vexans corresponds well with its greenhouse pathogenicity results, and its combination can be exploited to identify pathogenic P. vexans isolates. Using RAPD and ISSR primers, molecular characterisation indicated genetic diversity but could not distinguish isolates by geographical origin or pathogenicity. The pathogen P. vexans was verified by ITS1 and ITS4 molecular analysis, and the sequences were subsequently deposited in the NCBI database. In conclusion, the enzyme activity relevant to pathogenicity (CL, CAT and APX) in conjunction with the invivo pathogenicity assay might be utilised to differentiate between pathogenic (virulent) and non-pathogenic (avirulent) P. vexans isolates and develop suitable disease management strategies.

Sequence Characteristics and Expression Analysis of the Gene Encoding Sedoheptulose-1,7-Bisphosphatase, an Important Calvin Cycle Enzyme in Upland Cotton (Gossypium hirsutum L.).

Sedoheptulose-1,7-bisphosphatase (SBPase, EC 3.1.3.37) is a key enzyme in the plant Calvin cycle and one of the main rate-limiting enzymes in the plant photosynthesis pathway. Many studies have demonstrated that the SBPase gene plays an important role in plant photosynthetic efficiency, yield, and stress responses; however, few studies have been conducted on the function and expression of the GhSBPase gene in upland cotton. In this study, our results showed that the coding sequence (CDS) of GhSBPase gene was 1182 bp, encoding a protein with 393 amino acids. The GhSBPase protein had adenosine monophosphate (AMP) binding site and a FIG (FBPase/IMPase/glpX) domain, and had six Cys residues and a CGGT(A/Q)C motif that were involved in redox regulation in plants. Evolutionarily, the GhSBPase protein clustered into the dicotyledon subgroup and was most closely related to the tomato SlSBPase protein. Western-blot analysis further indicated that the GhSBPase gene was indeed the gene encoding the SBPase protein in upland cotton. The GhSBPase protein was localized in chloroplast, which was consistent with its function as a key enzyme in photosynthesis. The GhSBPase gene was specifically highly expressed in leaves, and its expression level was significantly lower in a yellow-green leaf mutant than in the wild type. Moreover, the GhSBPase expression was in response to drought, salt, high- and low-temperature stress, and exhibits different expression patterns. The GhSBPase promoter had the cis-acting elements in response to abiotic stress, phytohormone, and light. In addition, the GhSBPase expression was positively correlated with the chlorophyll fluorescence parameters, suggesting that changes in the expression of the GhSBPase had potential applicability in breeding for enhanced cotton photosynthetic efficiency. These results will help to understand the function of the GhSBPase gene in photosynthesis and the adaptability of plants to external stress and provide important gene information for the high-yield breeding of crops in the future.

Comparing the salinity tolerance of twenty different wheat genotypes on the basis of their physiological and biochemical parameters under NaCl stress.

The climate has drastically changed over the past two decades. Rising temperatures and climate change may lead to increased evapotranspiration, specifically soil evaporation, causing water to evaporate and salt to accumulate in the soil, resulting in increased soil salinity. As a result, there is a need to evaluate methods for predicting and monitoring the effects of salinity on crop growth and production through rapid screening. Our study was conducted on 20 wheat genotypes, 10 sensitive and 10 tolerant, exposed to two salinity levels (90 and 120 mM NaCl) with the control under greenhouse conditions. Our results revealed significant differences in the genotypes' response to salinity. Salt stress decreased chlorophyll index in sensitive genotypes but increased chlorophyll a and carotenoids in tolerant genotypes at 90 mM. Salt stress also increased protein, proline, lipoxygenase, and reactive thiobarbituric acid levels in all wheat genotypes. The study suggests that plant photosynthetic efficiency is a reliable, non-destructive biomarker for determining the salt tolerance of wheat genotypes, while other biochemical traits are destructive and time-consuming and therefore not suitable for rapid screening.

Decreasing photosystem antenna size by inhibiting chlorophyll synthesis: A double-edged sword for photosynthetic efficiency

Improving photosynthetic efficiency has long been considered as an important strategy to increase crop yield. Optimization of antenna size of photosynthetic systems is one strategy to increase plant photosynthetic efficiency. However, applying this strategy to improve photosynthesis received conflicting results, and the reasons behind these conflicts are unclear. In this study, we constructed transgenic rice with amiRNA targeting to YGL1, which encodes a key enzyme of chlorophyll a/b synthesis in chlorophyll biosynthesis pathway, to generate different lines with different leaf chlorophyll contents and antenna sizes to test under what conditions reduction of antenna size can improve photosynthesis. We found that leaf photosynthesis, canopy photosynthesis (Ac), biomass and grain yield of the heterozygote were not significantly different from those of wild type (WT) while the Ac, biomass and yield of the homozygote were lower than those of WT. Further, when the maximal quantum yield of photosystem II (Fv/Fm) was larger than 0.8, decreasing antenna size by reducing chlorophyll biosynthesis didn't affect leaf photosynthesis. In view of this phenomenon, we proposed that the accumulation of protoporphyrin and the reduced photoprotection capacity might be the cause of the decrease in Fv/Fm and Ac. Therefore, this study shows that reduction of antenna size by inhibiting chlorophyll synthesis can lead to improved light distribution and photosystem efficiency, as long as photodamage and photobleaching can be avoided to maintain the photosystem II efficiency. The double-edged sword effect of inhibiting chlorophyll synthesis on photosynthetic efficiency should be considered when the antenna size is manipulated to gain higher photosynthesis.

Impact of engineering the ATP synthase rotor ring on photosynthesis in tobacco chloroplasts.

The chloroplast ATP synthase produces the ATP needed for photosynthesis and plant growth. The trans-membrane flow of protons through the ATP synthase rotates an oligomeric assembly of c subunits, the c-ring. The ion-to-ATP ratio in rotary F1F0-ATP synthases is defined by the number of c-subunits in the rotor c-ring. Engineering the c-ring stoichiometry is, therefore, a possible route to manipulate ATP synthesis by the ATP synthase and hence photosynthetic efficiency in plants. Here, we describe the construction of a tobacco (Nicotiana tabacum) chloroplast atpH (chloroplastic ATP synthase subunit c gene) mutant in which the c-ring stoichiometry was increased from 14 to 15 c-subunits. Although the abundance of the ATP synthase was decreased to 25% of wild-type (WT) levels, the mutant lines grew as well as WT plants and photosynthetic electron transport remained unaffected. To synthesize the necessary ATP for growth, we found that the contribution of the membrane potential to the proton motive force was enhanced to ensure a higher proton flux via the c15-ring without unwanted low pH-induced feedback inhibition of electron transport. Our work opens avenues to manipulate plant ion-to-ATP ratios with potentially beneficial consequences for photosynthesis.

Multi-objective optimal regulation model and system based on whole plant photosynthesis and light use efficiency of lettuce

Lettuce growth and light energy consumption in a plant factory with artificial lighting (PFAL) were studied, and whole plant photosynthetic rate (ACO2) and light use efficiency (LUE) data were obtained on different days after planting (DAP) under different photosynthetic photon flux densities (PPFDs). Genetic algorithm‐support vector regression (GA-SVR) was used to construct the ACO2 and LUE prediction models. The coefficient of determination (R2) between the predicted and measured values of the ACO2 model was 0.97 and the root mean square error (RMSE) was 0.42 μmol·mol−1·plant−1·min−1, and R2 between the predicted and measured values of the LUE model was 0.97 and RMSE was 0.36%. The ACO2 and LUE prediction models were used as the objective functions, and multi-objective search was performed by the non-dominated sorting genetic algorithm II (NSGA-II) and the distance-based knee point detection method were used to obtained the optimal equilibrium solution for different DAPs. The optimal equilibrium solutions were used as the basis to establish the light regulation model based on lettuce DAP with R2 of 0.99. To validate the effect of model regulation, a lettuce light regulation system was built using an artificial climate chamber for a 30-day system validation. The results showed that compared with the traditional quantitative light supplementation method, the dry matter of model regulation significantly increased by 39.23% and 29.48% compared with quantitative PPFD150 (μmol·m−2·s−1) and PPFD200 (μmol·m−2·s−1). Model regulation increased the number of total light quanta consumed by 1.39% over PPFD150 and decreased by 23.96% over PPFD200; however, plant productivity increased by 35.35% and 33.14%, respectively. Model regulation significantly reduced the number of light quanta consumed per unit mass of lettuce production by 24.35% for PPFD150 and 41.54% for PPFD200, and LUE of light-emitting diode energy into dry matter was significantly increased by 33.49% and 75.09%. Therefore, the light regulation model based on multi-objective optimization in this study could improve crop yield and increase LUE.

Effects of Ascorbic Acid on Physiological Characteristics during Somatic Embryogenesis of Fraxinus mandshurica

Fraxinus mandshurica is one of the precious tree species in northeast China and has important economic and ecological value. Ascorbic acid (ASA) is a strong antioxidant that can significantly improve plant photosynthetic efficiency and stress resistance and participate widely in plant growth and development. In this study, we investigated the development process of mature zygotic embryos of F. mandshurica under different concentrations of ASA and found that 100 mg·L-1 exogenous ASA was the optimal concentration and that the induction rate of somatic embryos (SEs) was the highest at 72.89%, which was 7.13 times higher than that of the control group. The polyphenol content, peroxidase (POD) activity, nitric oxide (NO) content, nitrate reductase (NR) activity, total ascorbic acid (T-ASA) content, ASA content, ASA/Dehydroascorbic acid (DHA) ratio, GSH/GSSG ratio, and ascorbate peroxidase (APX) activity were significantly increased under the application of exogenous ASA in explants, whereas the polyphenol oxidase (PPO) activity, phenylalanine ammonia-lyase (PAL) activity, superoxide dismutase (SOD) activity, and catalase (CAT) activity, malondialdehyde (MDA) content and nitric oxide synthase (NOS) activity were decreased. At the same time, the content of T-ASA and ASA, T-GSH and GSSG, and PAL and SOD had the same change pattern in the control group and the treatment group. These results suggested that high or low concentrations of ASA could not promote the somatic embryogenesis of F. mandshurica and that exogenous ASA had significant effects on the physiology of F. mandshurica explants. ASA was also highly related to somatic embryogenesis and the explant browning of F. mandshurica. Our results could provide a reference for further study on the browning mechanism of F. mandshurica explants and lay the foundation for optimizing the condition of somatic embryogenesis in F. mandshurica.

Exogenous application of proline and phosphorus help improving maize performance under salt stress

Salinity is one of the important abiotic stresses that challenge crop productivity worldwide. Crop nutrition management and exogenous application of proline may help improve plant salt tolerance. This study investigated the effects of exogenous proline (100 mM) and phosphorus (P; 10 and 100 mg kg−1 sand) application on the growth, P content and ionic balance in maize under salt stress. Seedlings of a maize hybrid 30Y87 were grown in sand-filled pots maintained under normal (1 dS m−1) and salt stress conditions (6 dS m−1). Salt stress caused a significant reduction in plant photosynthetic efficiency, plant growth, and shoot and root P contents and tissue potassium (K+) contents whereas a significant increase in tissue sodium (Na+) and chloride (Cl−) was also noted. However, the application of proline and P ameliorated the impact of salt stress by restricting the Na+ and Cl− uptake and accumulation, and significantly improved plant light absorption capacity, plant growth, P contents and tissue K+ contents under both control and salt stress conditions. In this regard, the application of proline with a high rate of P nutrition was more effective. In conclusion, co-application of proline with a high rate of P nutrition synergistically restricted the Na+ and Cl− accumulation and improved the plant growth under salt stress.