Showing papers on "Plant physiology published in 2021"

Drought Tolerance Strategies in Plants: A Mechanistic Approach

Abstract: Anthropogenic activities in the past and present eras have created global warming and consequently a storm of drought stress, affecting both plants and animals Being sessile, plants are more vulnerable to drought stress and consequently reduce plant growth and yield To mitigate the effects of drought stress on plants, it is very crucial to determine the plant response mechanisms against drought stress Drought response mechanism includes morph-physiological, biochemical, cellular and molecular processes takes place in plants underlying drought stress These processes include improvement in root system, leaf structure, osmotic adjustment, relative water content and stomata regulation In addition, calcium and phytohormone (Abscisic acid, Jasmonic acid, Salicylic acid, Auxins, Gibberellins, Ethylene etc) signaling pathways and scavenging of reactive oxygen species are the key mechanisms to cope with drought stress Moreover, microorganisms such as bacteria and fungi also have an important role in drought tolerance enhancement To further elucidate and improve drought tolerance in plants, quantitative trait loci, transgenic approach and application of exogenous substances (nitric oxide, 24-epibrassinoide, glycine betaine and proline) are very crucial Hereby, the present study integrates various mechanisms of drought tolerance in plants

Copper Nanoparticle Application Enhances Plant Growth and Grain Yield in Maize Under Drought Stress Conditions

Abstract: Abiotic stresses, including drought, detrimentally affect the growth and productivity of many economically important crop plants, leading to significant yield losses, which can result in food shortages and threaten the sustainability of agriculture. Balancing plant growth and stress responses is one of the most important functions of agricultural application to optimize plant production. In this study, we initially report that copper nanoparticle priming positively regulates drought stress responses in maize. The copper nanoparticle priming plants displayed enhanced drought tolerance indicated by their higher leaf water content and plant biomass under drought as compared with water-treated plants. Moreover, our data showed that the treatment of copper nanoparticle on plants increased anthocyanin, chlorophyll and carotenoid contents compared to water-treated plants under drought stress conditions. Additionally, histochemical analyses with nitro blue tetrazolium and 3,3′-diaminobenzidine revealed that reactive oxygen species accumulation of priming plants was decreased as a result of enhancement of reactive oxygen species scavenging enzyme activities under drought. Furthermore, our comparative yield analysis data indicated applying copper nanoparticles to the plant increased total seed number and grain yield under drought stress conditions. Our data suggest that copper nanoparticle regulates plant protective mechanisms associated with drought tolerance, which is a promising approach for the production of drought-tolerant crop plants.

Plasma membrane H+-ATPase overexpression increases rice yield via simultaneous enhancement of nutrient uptake and photosynthesis

Abstract: Nitrogen (N) and carbon (C) are essential elements for plant growth and crop yield. Thus, improved N and C utilisation contributes to agricultural productivity and reduces the need for fertilisation. In the present study, we find that overexpression of a single rice gene, Oryza sativa plasma membrane (PM) H+-ATPase 1 (OSA1), facilitates ammonium absorption and assimilation in roots and enhanced light-induced stomatal opening with higher photosynthesis rate in leaves. As a result, OSA1 overexpression in rice plants causes a 33% increase in grain yield and a 46% increase in N use efficiency overall. As PM H+-ATPase is highly conserved in plants, these findings indicate that the manipulation of PM H+-ATPase could cooperatively improve N and C utilisation, potentially providing a vital tool for food security and sustainable agriculture.

Influence of nano-priming on seed germination and plant growth of forage and medicinal plants

Abstract: Plant growth and development are vastly affected by different abiotic and biotic stresses. Seed priming is an effective tool for increasing seed germination and plant growth that will eventually increase productivity under different environmental conditions and stresses. Efficient seed germination promotes successful establishment and deep root system of plants. Among the different seed priming methods, nano-priming is more effective mainly because of its small size and unique physicochemical properties. Since plant species are physiologically different, they differ in their uptake of nanoparticles in nano-priming, and hence in their rate and manner of growth. Most previous studies have separately investigated the effect of nanomaterial on seed germination, growth, and development of one plant at a time. However, very few studies have reported nano-priming effects using different particles on seed germination and seedling growth of forage and medicinal plants together. Therefore, this review summarizes studies of nano-priming effects using various particles on seed germination and seedling growth of forage and medicinal plants. Furthermore, the effect of different nanoparticles on the most important characteristics of germination, morphology and physiology affecting the establishment, growth and production of these plants are reviewed. In general, nano-priming increased seed germination, seedling growth and development, vigor, rate of seedling emergence and subsequent performance in most of the medicinal and forage plants. While the use of nanoparticles enhanced environmental stress resistance of these plants, negative effects of nano-priming on seed germination, seedling and plant growth traits were observed. In addition, future research areas of focus are discussed briefly.

Microplastics in soil-plant system: effects of nano/microplastics on plant photosynthesis, rhizosphere microbes and soil properties in soil with different residues

Abstract: To investigate the effects of polystyrene microplastics (PS-beads) on the soil properties, photosynthesis of Flowering Chinese cabbage, the rhizosphere microbial community and their potential correlation in soil with different residues. The influences of PS-beads (PS-MPs, M1, 5 μm; PS-NPs, M2, 70 nm) on the plant photosynthesis and growth parameters, soil dissolved organic matter (DOM) and the characteristic functional groups, the microbial community and metabolism prediction were studied by a pot-experiment in soil without residues (N), with biochar (B), degradable mulching film (DMF) fragments (D), or biochar and DMF (BD). Chlorophyll a was more susceptible to the exogenous substances than Chlorophyll b. In soil with different residues, PS-beads of different sizes could change different components, structures and functional groups in aromatic rings of DOM, might further change the microbial community and metabolism. M2 decreased TDN and NO3− and increased the weight of the plant in group D. M2 increased the weight of the plant in group N. M2 decreased the net photosynthetic rate in group B. The different sizes of PS-beads affected the different parameters of plant growth and potentially changed the plant growth and photosynthetic parameters through altering the microbial metabolism and the correlation among microbes. The potential mechanisms of PS-beads changing the plant growth were different in soil with different residues. Our results evidenced the PS-beads potentially changed the plant growth and photosynthesis by changing the microbial metabolism and the correlation among microbes.

Copper: uptake, toxicity and tolerance in plants and management of Cu-contaminated soil

Abstract: Copper (Cu) is an essential mineral nutrient for the proper growth and development of plants; it is involved in myriad morphological, physiological, and biochemical processes. Copper acts as a cofactor in various enzymes and performs essential roles in photosynthesis, respiration and the electron transport chain, and is a structural component of defense genes. Excess Cu, however, imparts negative effects on plant growth and productivity. Many studies have summarized the adverse effects of excess Cu on germination, growth, photosynthesis, and antioxidant response in agricultural crops. Its inhibitory influence on mineral nutrition, chlorophyll biosynthesis, and antioxidant enzyme activity has been verified. The current review focuses on the availability and uptake of Cu by plants. The toxic effects of excess Cu on seed germination, plant growth and development, photosynthesis, and antioxidant response in plants are discussed. Plant tolerance mechanisms against Cu stress, and management of Cu-contaminated soils are presented.

Anthocyanins are Key Regulators of Drought Stress Tolerance in Tobacco.

Abstract: Abiotic stresses will be one of the major challenges for worldwide food supply in the near future. Therefore, it is important to understand the physiological mechanisms that mediate plant responses to abiotic stresses. When subjected to UV, salinity or drought stress, plants accumulate specialized metabolites that are often correlated with their ability to cope with the stress. Among them, anthocyanins are the most studied intermediates of the phenylpropanoid pathway. However, their role in plant response to abiotic stresses is still under discussion. To better understand the effects of anthocyanins on plant physiology and morphogenesis, and their implications on drought stress tolerance, we used transgenic tobacco plants (AN1), which over-accumulated anthocyanins in all tissues. AN1 plants showed an altered phenotype in terms of leaf gas exchanges, leaf morphology, anatomy and metabolic profile, which conferred them with a higher drought tolerance compared to the wild-type plants. These results provide important insights for understanding the functional reason for anthocyanin accumulation in plants under stress.

Arbuscular Mycorrhiza Improves Photosynthesis and Restores Alteration in Sugar Metabolism in Triticum aestivum L. Grown in Arsenic Contaminated Soil.

Abstract: Contamination of agricultural soil by arsenic (As) is a serious menace to environmental safety and global food security. Symbiotic plant-microbe interaction, such as arbuscular mycorrhiza (AM), is a promising approach to minimize hazards of As contamination in agricultural soil. Even though the potential of AM fungi (AMF) in redeeming As tolerance and improving growth is well recognized, the detailed metabolic and physiological mechanisms behind such beneficial effects are far from being completely unraveled. The present study investigated the ability of an AM fungus, Rhizophagus intraradices, in mitigating As-mediated negative effects on photosynthesis and sugar metabolism in wheat (Triticum aestivum) subjected to three levels of As, viz., 0, 25, and 50 mg As kg-1 of soil, supplied as sodium arsenate. As exposure caused significant decrease in photosynthetic pigments, Hill reaction activity, and gas exchange parameters such as net photosynthetic rate, stomatal conductance, transpiration rate, and intercellular CO2 concentration. In addition, As exposure also altered the activities of starch-hydrolyzing, sucrose-synthesizing, and sucrose-degrading enzymes in leaves. Colonization by R. intraradices not only promoted plant growth but also restored As-mediated impairments in plant physiology. The symbiosis augmented the concentration of photosynthetic pigments, enhanced Hill reaction activity, and improved leaf gas exchange parameters and water use efficiency of T. aestivum even at high dose of 50 mg As kg-1 of soil. Furthermore, inoculation with R. intraradices also restored As-mediated alteration in sugar metabolism by modulating the activities of starch phosphorylase, α-amylase, β-amylase, acid invertase, sucrose synthase, and sucrose-phosphate synthase in leaves. This ensured improved sugar and starch levels in mycorrhizal plants. Overall, the study advocates the potential of R. intraradices in bio-amelioration of As-induced physiological disturbances in wheat plant.

Mechanistic Elucidation of Salicylic Acid and Sulphur-Induced Defence Systems, Nitrogen Metabolism, Photosynthetic, and Growth Potential of Mungbean (Vigna radiata) Under Salt Stress

Abstract: The potential of plant nutrients (such as sulphur, S) and phytohormones (such as salicylic acid, SA) has been explored in isolated studies by researchers in controlling the impact of abiotic stresses such as salinity in plants. However, information is scanty on the major mechanisms underlying the role of S and/or SA in modulation of enzymes involved in nitrogen (N) assimilation, GOGAT cycle, and antioxidant defence system; the cellular status of N-containing osmolyte proline, glucose, S-containing compounds; and their cumulative role in photosynthesis functions and growth in crop plants. The present study aimed to assess the role of cumulative effect of SA and S (SO42−) mediated induction of N assimilatory enzymes, GOGAT cycle, N-osmolyte proline and its metabolizing enzymes, glyoxylase enzymes, and antioxidant capacity in mungbean (Vigna radiata L.) exposed to NaCl with or without SO42− and SA. Salt-exposed V. radiate showed differential elevations in damage (O.2−, H2O2, lipid peroxidation; glucose) and defence (ascorbate peroxidase, APX; glutathione reductase, GR; superoxide dismutase, SOD; reduced GSH; proline) and inhibitions in the activities of NR and NiR; N content, photosynthesis, photosynthetic N-use-efficiency (NUE), and growth. The separate supplementation of SA and SO42− to 50 mM NaCl almost equally strengthened the antioxidant machinery and diminished NaCl-accrued damages. However, combined supply of SA and SO42− to NaCl-exposed cultivars led to significant improvements in NR and NiR activities, the accumulation of N, GSH, proline, enhanced activity of APX, GR, and reduced activity of SOD, and also decreases in O.2−, H2O2, lipid peroxidation and glucose. These observations were corroborated with SA, SO42− and NaCl-mediated changes in the traits of photosynthesis and growth, stomatal behaviour, and the polypeptide patterns of Rubisco in V. radiata. Overall, in V. radiata, SA-mediated higher enhancements in the activity of N assimilatory enzymes (NR, NiR, and GS), increase in the N and proline, and GSH; and decreases in the contents of Na+ and Cl− ions, and glucose (a photosynthesis repressor); maintenance of a fine tuning among SOD, APX, and GR enzymes; and higher minimization of ROS (O.2−, H2O2) and lipid peroxidation finally led to a higher promotion in photosynthesis and growth.

Microalgae-cyanobacteria–based biostimulant effect on salinity tolerance mechanisms, nutrient uptake, and tomato plant growth under salt stress

Abstract: High soil salinity is a major abiotic stress affecting the growth, nutrition, development, and productivity of crops. This study investigated the modulating effect of combined microalgae-cyanobacteria extract formulations (MEF1%, MEF5%, and MEF10%) prepared from the species Dunaliella salina, Chlorella ellipsoidea, Aphanothece sp., and Arthrospira maxima, on tomato plant growth and tolerance under four NaCl concentrations (0, 80, 120, and 150 mM). MEF5% enhanced the vegetative growth of tomato plants, characterized by higher shoot and root weight and larger leaf area. According to principal component analysis (PCA), improved plant growth was closely associated with leaf photosynthetic pigments, which was mainly due to improved osmotic adjustment and ion homeostasis. Proline accumulation was significantly enhanced by MEF5%-treatment in plants grown under 120 mM and 150 mM NaCl conditions. MEF5%-treatment also significantly improved nitrogen (N), phosphorus (P), and potassium (K+) absorption in plants grown at 80 mM and 120 mM NaCl levels. Leaf lipid peroxidation through ROS oxidative stress significantly decreased with enhanced CAT and SOD activities in MEF5%-treated plants. MEF5% triggered a significant decline in fatty acid content, indicating fatty acid transformation into other lipid forms such as alkanes, which are essential in the cuticular wax synthesis of hydric stressed plants. Enhanced K+ uptake and reduced Na+/K+ ratio in the leaves of treated plants indicate MEF’s active role in reestablishing ion homeostasis. Nutrient uptake can be improved by enhanced root biomass, which subsequently increases the roots’ surface for nutrient absorption. These results indicate that MEF stimulated plant growth and tolerance responses through (i) enhanced antioxidant enzyme activities and (ii) improved root growth and nutrient uptake. Therefore, combined microalgae-cyanobacteria formulations could be another sustainable alternative to boost nutrient uptake, growth, and crop adaptability under normal and saline conditions.

Comparative Transcriptomics and Metabolomics Reveal an Intricate Priming Mechanism Involved in PGPR-Mediated Salt Tolerance in Tomato.

Abstract: Plant-associated beneficial strains inhabiting plants grown under harsh ecosystems can help them cope with abiotic stress factors by positively influencing plant physiology, development, and environmental adaptation. Previously, we isolated a potential plant growth promoting strain (AXSa06) identified as Pseudomonas oryzihabitans, possessing 1-aminocyclopropane-1-carboxylate deaminase activity, producing indole-3-acetic acid and siderophores, as well as solubilizing inorganic phosphorus. In this study, we aimed to further evaluate the effects of AXSa06 seed inoculation on the growth of tomato seedlings under excess salt (200 mM NaCl) by deciphering their transcriptomic and metabolomic profiles. Differences in transcript levels and metabolites following AXSa06 inoculation seem likely to have contributed to the observed difference in salt adaptation of inoculated plants. In particular, inoculations exerted a positive effect on plant growth and photosynthetic parameters, imposing plants to a primed state, at which they were able to respond more robustly to salt stress probably by efficiently activating antioxidant metabolism, by dampening stress signals, by detoxifying Na+, as well as by effectively assimilating carbon and nitrogen. The primed state of AXSa06-inoculated plants is supported by the increased leaf lipid peroxidation, ascorbate content, as well as the enhanced activities of antioxidant enzymes, prior to stress treatment. The identified signatory molecules of AXSa06-mediated salt tolerance included the amino acids aspartate, threonine, serine, and glutamate, as well as key genes related to ethylene or abscisic acid homeostasis and perception, and ion antiporters. Our findings represent a promising sustainable solution to improve agricultural production under the forthcoming climate change conditions.

Alleviation of Field Low-Temperature Stress in Winter Wheat by Exogenous Application of Salicylic Acid

Abstract: Low temperature in later spring severely limits plant growth and causes considerable yield loss in wheat. In this study, the impacts of exogenous salicylic acid (SA) on plant growth, grain yield and key physiological parameters of wheat plants were investigated under field low-temperature conditions using a field air temperature control system (FATC). The results showed that low-temperature stress significantly decreased leaf net photosynthetic rate, plant height and biomass production of wheat plants at the jointing stage, resulting in a reduction in grain yield. Moreover, the growth period of wheat plants was prolonged by low-temperature stress. However, SA-treated plants significantly improved the photochemical efficiency of photosystem II, accumulation of osmo-protectants, activities of enzymatic antioxidants, and pool of non-enzymatic low molecular substances compared with non-SA-treated plants under low-temperature stress. Pretreatment with SA effectively alleviated low-temperature-induced reduction in leaf net photosynthetic rate, plant height, biomass production and grain yield as well as prolonging of growth period of wheat plants. However, SA-treated plants had no significant effects on the expression levels of cold-responsive genes compared with non-SA-treated plants under low-temperature stress. Our results demonstrated that exogenous application of SA is an appropriate strategy for wheat to resist late spring low-temperature stress under field conditions.

The effect of light quality on plant physiology, photosynthetic, and stress response in Arabidopsis thaliana leaves

Abstract: The impacts of wavelengths in 500-600 nm on plant response and their underlying mechanisms remain elusive and required further investigation. Here, we investigated the effect of light quality on leaf area growth, biomass, pigments content, and net photosynthetic rate (Pn) across three Arabidopsis thaliana accessions, along with changes in transcription, photosynthates content, and antioxidative enzyme activity. Eleven-leaves plants were treated with BL; 450 nm, AL; 595 nm, RL; 650 nm, and FL; 400-700 nm as control. RL significantly increased leaf area growth, biomass, and promoted Pn. BL increased leaf area growth, carotenoid and anthocyanin content. AL significantly reduced leaf area growth and biomass, while Pn remained unaffected. Petiole elongation was further observed across accessions under AL. To explore the underlying mechanisms under AL, expression of key marker genes involved in light-responsive photosynthetic reaction, enzymatic activity of antioxidants, and content of photosynthates were monitored in Col-0 under AL, RL (as contrast), and FL (as control). AL induced transcription of GSH2 and PSBA, while downregulated NPQ1 and FNR2. Photosynthates, including proteins and starches, showed lower content under AL. SOD and APX showed enhanced enzymatic activity under AL. These results provide insight into physiological and photosynthetic responses to light quality, in addition to identifying putative protective-mechanisms that may be induced to cope with lighting-stress in order to enhance plant stress tolerance.

Hydrogen Sulfide–Phytohormone Interaction in Plants Under Physiological and Stress Conditions

Abstract: Hydrogen sulfide (H2S), as a novel gaseous signalling molecule, has been extensively investigated in plants ranging from seed germination to senescence. Phytohormones, including stimulator (such as auxin: AUX; gibberellin: GA; cytokinin: CTK; and melatonin: MEL) and inhibitor (such as ethylene: ETH; abscisic acid: ABA; salicylic acid: SA; and jasmonic acid: JA) types, as universal regulators, play a key role in the plant growth, development, and response and adaptation to adverse environments. Now, phytohormones are considered to be the key targets for improving plant productivity and stress tolerance, which affect the production and quality of crop plants. These indicate the interaction of H2S with phytohormones in many physiological processes such as seed germination, seedling establishment, plant growth, development, and senescence, as well as response to environmental stress. However, the molecular mechanism of H2S–phytohormone interaction is not completely clear. In this review, the interaction of H2S with stimulator hormones (AUX, GA, and MEL) and inhibitor hormones (ETH, ABA, SA, and JA) in plants under physiological and stress conditions was discussed. The H2S–phytohormone interaction not only highlighted H2S-mediated phytohormone signaling in stomatal development and closure, fruit ripening, organ abscission, as well as heat, chilling, salt, cadmium, iron deficiency, and boron tolerance; but also focused on the phytohormone-mediated H2S signaling in seed germination, root development, stomatal closure, fruit ripening, organ abscission, as well as drought, chilling, and cadmium tolerance. The aim is to arouse the rapid development of the research on H2S, phytohormones, and their interaction in plant biology field, laying the foundation of acquiring transgenic crop plants with high yield, high quality, and multiple stress tolerance.

Salicylic acid alleviates chromium (VI) toxicity by restricting its uptake, improving photosynthesis and augmenting antioxidant defense in Solanum lycopersicum L

Abstract: Contamination of agricultural soil by chromium (Cr) is a serious menace to environmental safety and global food security. Although potential of salicylic acid (SA) in mitigating heavy metal (HM) toxicity in plants is well recognized, detailed physiological mechanisms behind such beneficial effects under Cr-stress in tomato (Solanum lycopersicum L.) plant are far from being completely unravelled. The present study evaluated the efficacy of exogenously applied SA, in alleviating Cr-mediated alterations on photosynthesis and antioxidant defense in tomato exposed to three different concentrations of Cr(VI) [0, 50, and 100 mg Cr(VI) kg−1 soil]. Exposure of tomato plants to Cr resulted in increased Cr-accumulation and oxidative damage, as signposted by high Cr concentration in root as well as shoot, augmented malondialdehyde (MDA) and superoxides levels, and inhibition in enzymes of ascorbate–glutathione (AsA-GSH) cycle. Furthermore, a significant (P ≤ 0.05) reduction in photosynthetic pigments and gas exchange parameters was also evident in Cr-stressed tomato plants. Findings of the present study showed that exogenous application of 0.5 mM SA not only promoted plant growth subjected to Cr, but also restored Cr-mediated disturbances in plant physiology. A significant (P ≤ 0.05) decrease in Cr acquisition and translocation as evidenced by improved growth and photosynthesis in SA-treated plants was observed. Additionally, exogenous SA application by virtue of its positive effect on efficient antioxidant system ameliorated the Cr-mediated oxidative stress in tomato plants as signposted by lower MDA and superoxide levels and improved AsA-GSH cycle. Overall, current study advocates the potential of exogenous SA application in amelioration of Cr-mediated physiological disturbances in tomato plant.

Improving salinity tolerance in Salvia officinalis L. by foliar application of salicylic acid

Abstract: Higher absorption and translocation of sodium (Na) and chlorine (Cl) ions in plant tissue can lead to serious physiological and biochemical changes. However, salicylic acid (SA) is a natural signaling molecule responsible for the induction of environmental stress tolerance in plants. Spraying SA could provide protection against several types of stress such as salinity. This study aimed to show the influence of SA spraying (0.5 and 1 mM) on the damaging effects of NaCl toxicity (150 mM) in Salvia officinalis L. plants. The results showed that salinity strongly inhibited the growth of aerial and root parts and this inhibition was accompanied by a significant decrease in the production of chlorophyll pigments (by 63%). There was also a significant accumulation of Na, mainly in the roots. This accumulation of Na+ ions was accompanied by a decrease of calcium (Ca), potassium (K) and phosphorus (P) concentrations. However, SA mainly at 0.5 mM, greatly improved plant growth, essential oils and chlorophyll pigments synthesis. Besides, SA led to a decrease in Na content and an improvement in Ca, K and P content in the leaves and roots. Salt stress decreased the essential oil yield from 1.2% (control) to 0.4% (NaCl). Furthermore, gas chromatography–mass spectrometry analysis of essential oils exhibited that the 1,8-cineol, α-thujone, and camphor were identified as the main components of essential oils under all treatments. However, we noted in stressed plant treated or not with SA the appearance of the new majority compound thujanone. Salt stress decreased the major compounds content. SA spray under stress condition increased the content of major compounds compared to stressed plants untreated with SA. The histological study in scanning electron microscopy showed the peltate glands density decreased strongly under NaCl toxicity. However, SA application on stressed plants increased peltate glands density. On the other hand, the glands of stressed plants often show certain anomalies in the morphology: the first anomaly observed was the presence of glandular structures characterized by deformations in the form of small protuberances located on the head of the gland. The second, a less common abnormality is the morphological change in certain glands that change from a spherical to an ovoid shape. On another hand, all these anomalies were not detected in stressed plants sprayed with SA. Therefore, the absence of these anomalies under the effect of SA showed the repairing effect of this growth regulator. The findings of the present work suggest that spraying of SA may be useful for improving the plant growth in NaCl-contaminated areas.

Impact of melatonin and tryptophan on water stress tolerance in white lupine (Lupinus termis L.).

Abstract: Melatonin has been identified as a signal molecule that regulates plant responses to different abiotic and biotic stresses. Melatonin (MT) and its precursor tryptophan (Try) have a major role in improving plant stress tolerance to different environmental stresses such as water deficiency. The rapid increase in the Egyptian population caused insufficient protein sources, especially those of animal origin, in their diet. The possible solution is to augment the diet with legumes such as white lupine which are relatively rich in protein. Thus, the current experimental work was carried out to find changes in growth, biochemical aspects and yield quantity and quality of white lupine plant with spraying of both MT and Try at different concentrations on plant shoot under water deficit stress conditions. Results showed that water deficit (75 or 50% of water irrigation requirements; WIR) caused significant reduction in growth, photosynthetic pigments, indole acetic acid and yield compared with those received 100% WIR. Seed yield significantly decreased (p < 0.05) by 26.98 and 41.64% by decreasing WIR to 75 and 50%. The decrease was accompanied by significant increase in phenolic contents, hydrogen peroxide, lipid peroxidation and some antioxidant enzymes, while nitrate reductase enzyme was decreased. However, external application of either MT or Try significantly alleviated the adverse effects of water deficit (growth suppression), since MT or Try-treated plants recovered more quickly than untreated plants. Moreover, MT or Try—treated plants had higher photosynthetic pigments, indole acetic acid, phenolic, as well as yield quantity and quality under the three WIR as compared with untreated plants. Melatonin treatment at 100 µM and Tryptophan at 200 µM increased weight of seeds/plant by 78.29 and 52.19%, 71.49 and 43.78% and 41.21 and 13.07% in plants irrigated with 100, 75 and 50% WIR, respectively. Exogenous MT and Try significantly reduced hydrogen peroxide and malondialdehyde content, while markedly increased the activities of antioxidant enzymes and nitrate reductase under different WIR. Finally, the current study concluded that MT and Try treatments alleviated the detrimental effects of water deficiency and accelerated the recovery mainly via improving white lupine plants tolerance in forms of enhancing photosynthetic pigments, indole acetic acid, phenolic and antioxidant capacity.

Combination of Red and Blue Lights Improved the Growth and Development of Eggplant (Solanum melongena L.) Seedlings by Regulating Photosynthesis

Abstract: The photosynthesis, photomorphogenesis, and photoperiod processes in plants are regulated according to light intensity and quality. The aim of this study was to investigate the effects of different light qualities on eggplant seedlings and determine the best light quality for growth. The seedlings of eggplant cultivar ‘Jingqiejingang’ were grown under light-emitting diodes (LEDs): white (W, the control), red (R), blue (B), and different ratios of B/R lights (B/R = 1/1, B/R = 1/3, B/R = 1/6, B/R = 1/9). The growth parameters, leaf morphology, photosynthetic performance, chlorophyll fluorescence, and the carbon and nitrogen metabolism in the leaves of eggplant seedlings under different LED light treatments were studied. The results showed that the plant height, leaf development, and photosynthetic characteristics were inhibited by red light but elevated by blue light compared with the control. Conversely, the contents of chlorophyll a, chlorophyll b, and carotenoids were all increased by red light, while decreased by blue light significantly. In addition, the contents of carbohydrates and the activities of nitrogen assimilation enzymes were not or little changed by the monochromatic blue and red light. The combined light of red and blue were more beneficial for growth than the monochromatic light, especially B/R = 1/3 light. Under B/R = 1/3 light, the parameter values of plant growth, leaf development, photosynthetic pigments and characteristics, and carbon and nitrogen metabolism were all maximum. Taken together, combined application lights of red and blue are good practice for the cultivation of eggplant seedlings, and LED B/R = 1/3 light was optimum.

Inoculation of Rhizobium Alleviates Salinity Stress Through Modulation of Growth Characteristics, Physiological and Biochemical Attributes, Stomatal Activities and Antioxidant Defence in Cicer arietinum L.

Abstract: Rhizobium is a plant growth-promoting bacteria, generally involved in nitrogen fixation and promotes growth in plants under abiotic-stressed conditions such as salinity. The present study investigates the significance of Rhizobium application in alleviation of salt stress in chickpea by increasing cell viability, stomatal movement, photosynthetic pigment and protein content, nitrate reductase, carbonic anhydrase as well as enzymatic and non-enzymatic antioxidant activities. Healthy and viable seeds were inoculated with Rhizobium before sowing. Salt treatment was given in terms of NaCl (50 or 150 mM) to the plants through soil at 20 days after sowing. High NaCl level (150 mM) reduced the growth attributes, pigment as well as soluble protein content, altered stomatal behaviour, reduced cell viability and enhanced the formation of superoxide radicals and other reactive oxygen species in foliage. Moreover, Rhizobium inoculation improved the mineral uptake, reduced electrolyte leakage which directly influences photosynthesis and improved yield attributes in the salt-treated chickpea plants. Therefore, Rhizobium could be applied to chickpea plants for efficient growth under salt stress.

Lycopene β-cyclase expression influences plant physiology, development, and metabolism in tobacco plants

Abstract: Carotenoids are important isoprenoids produced in the plastids of photosynthetic organisms that play key roles in photoprotection and antioxidative processes. β-Carotene is generated from lycopene by lycopene β-cyclase (LCYB). Previously, we demonstrated that the introduction of the Daucus carota (carrot) DcLCYB1 gene into tobacco (cv. Xanthi) resulted in increased levels of abscisic acid (ABA) and especially gibberellins (GAs), resulting in increased plant yield. In order to understand this phenomenon prior to exporting this genetic strategy to crops, we generated tobacco (Nicotiana tabacum cv. Petit Havana) mutants that exhibited a wide range of LCYB expression. Transplastomic plants expressing DcLCYB1 at high levels showed a wild-type-like growth, even though their pigment content was increased and their leaf GA1 content was reduced. RNA interference (RNAi) NtLCYB lines showed different reductions in NtLCYB transcript abundance, correlating with reduced pigment content and plant variegation. Photosynthesis (leaf absorptance, Fv/Fm, and light-saturated capacity of linear electron transport) and plant growth were impaired. Remarkably, drastic changes in phytohormone content also occurred in the RNAi lines. However, external application of phytohormones was not sufficient to rescue these phenotypes, suggesting that altered photosynthetic efficiency might be another important factor explaining their reduced biomass. These results show that LCYB expression influences plant biomass by different mechanisms and suggests thresholds for LCYB expression levels that might be beneficial or detrimental for plant growth.

Impact of silicon dioxide nanoparticles on growth, photosynthetic pigments, proline, activities of defense enzymes and some bacterial and fungal pathogens of tomato

Abstract: The effects of silicon dioxide nanoparticles (SiO2 NPs) in two concentrations (0.10 and 0.20 gL− 1) as foliar spray and seed priming was observed on plant growth attributes, chlorophyll, carotenoid, proline, activities of defense enzymes of tomato and on bacterial pathogens i.e. Pseudomonas syringae pv. tomato (Pst), Xanthomonas campestris pv. vesicatoria (Xcv), Pectobacterium carotovorum subsp. carotovorum (Pcc) and Ralstonia solanacearum (Rs), and fungal pathogens i.e. Fusarium oxysporum f. sp. lycopersici (Fol) and Alternaria solani (As) under in vitro and greenhouse conditions. Disease suppression and increase in plant growth was dependent on concentration of NPs and mode of application. Foliar spray was more effective than seed priming in increasing plant growth, chlorophyll, carotenoid, proline and activities of defense enzymes i.e. superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and phenylalanine ammonia lyase (PAL) in the presence and absence of pathogens. Foliar spray of 0.20 gL− 1SiO2 NPs caused highest increase in plant growth parameters, chlorophyll, carotenoid, proline and activities of defense enzymes in tomato plants and caused maximum reduction in disease indices. In vitro tests and scanning electron microscopy revealed antimicrobial effects of SiO2 NPs with varied adverse effects on pathogens under study. Plants subjected to foliar spray with 0.20 gL− 1SiO2 NPs had more plant growth attributes, chlorophyll, carotenoid, proline and defense enzymes against pathogens under study.

Physiological and transcriptome analyses for assessing the effects of exogenous uniconazole on drought tolerance in hemp (Cannabis sativa L.)

Abstract: Uniconazole (S-(+)-uniconazole), a plant growth retardant, exerts key roles in modulating growth and development and increasing abiotic stress tolerance in plants. However, the underlying mechanisms by which uniconazole regulates drought response remain largely unknown. Here, the effects of exogenous uniconazole on drought tolerance in hemp were studied via physiological and transcriptome analyses of the drought-sensitive industrial hemp cultivar Hanma No. 2 grown under drought stress. Exogenous uniconazole treatment increased hemp tolerance to drought-induced damage by enhancing chlorophyll content and photosynthesis capacity, regulating activities of enzymes involved in carbon and nitrogen metabolism, and altering endogenous hormone levels. Expression of genes associated with porphyrin and chlorophyll metabolism, photosynthesis-antenna proteins, photosynthesis, starch and sucrose metabolism, nitrogen metabolism, and plant hormone signal transduction were significantly regulated by uniconazole compared with that by control (distilled water) under drought stress. Numerous genes were differentially expressed to increase chlorophyll content, enhance photosynthesis, regulate carbon-nitrogen metabolism-related enzyme activities, and alter endogenous hormone levels. Thus, uniconazole regulated physiological and molecular characteristics of photosynthesis, carbon-nitrogen metabolism, and plant hormone signal transduction to enhance drought resistance in industrial hemp.

Effect of Hydrogen Peroxide on Plant Growth, Photosynthesis, Leaf Histology and Rubisco Gene Expression of the Ficus deltoidea Jack Var. deltoidea Jack

Abstract: The present study was carried out to investigate the effects of hydrogen peroxide (H2O2) on the growth, photosynthesis, leaf histology, mineral uptake, phytochemical accumulation, and Rubisco gene expression in Ficus deltoidea var. deltoidea, a slow growing medicinal plant. The F. deltoidea plants were spray-treated with 0 (control), 8, 16, 30 and 60 mM H2O2 under field conditions. The results showed that the applications of 30 mM H2O2 increased the plant height, leaf number, and syconium number by 26%, 9% and 2275%, respectively, over the control specimen. Photosynthetic rates, transpiration, stomatal conductance and chlorophyll content of F. deltoidae plants increased significantly after treatment of 30 mM H2O2. A lower concentration (8 and 16 mM) of H2O2 also improved the leaf histological properties such as tracheary elements and other vascular cells. In addition, treatments with 30 mM H2O2 increased calcium, potassium, total phenolic and flavonoids content, in F. deltoidea plants, by 14%, 15%, 12% and 72%, respectively. In addition, H2O2 treatment at 30 mM concentration downregulated the Rubisco gene with a between 1 and 5 times fold gene expression change. From this study, it can be concluded that spraying with 30 and 16 mM of H2O2 once a week enhanced growth, photosynthesis, mineral accumulation, phenol and flavonoid content, as well as aided Rubisco gene expression, under field conditions.

Photosynthesis of the Cyanidioschyzon merolae cells in blue, red, and white light

Abstract: Photosynthesis and respiration rates, pigment contents, CO2 compensation point, and carbonic anhydrase activity in Cyanidioschizon merolae cultivated in blue, red, and white light were measured. At the same light quality as during the growth, the photosynthesis of cells in blue light was significantly lowered, while under red light only slightly decreased as compared with white control. In white light, the quality of light during growth had no effect on the rate of photosynthesis at low O2 and high CO2 concentration, whereas their atmospheric level caused only slight decrease. Blue light reduced markedly photosynthesis rate of cells grown in white and red light, whereas the effect of red light was not so great. Only cells grown in the blue light showed increased respiration rate following the period of both the darkness and illumination. Cells grown in red light had the greatest amount of chlorophyll a, zeaxanthin, and β-carotene, while those in blue light had more phycocyanin. The dependence on O2 concentration of the CO2 compensation point and the rate of photosynthesis indicate that this alga possessed photorespiration. Differences in the rate of photosynthesis at different light qualities are discussed in relation to the content of pigments and transferred light energy together with the possible influence of related processes. Our data showed that blue and red light regulate photosynthesis in C. merolae for adjusting its metabolism to unfavorable for photosynthesis light conditions.

Nitric Oxide-Mediated Enhancement in Photosynthetic Efficiency, Ion Uptake and Carbohydrate Metabolism that Boosts Overall Photosynthetic Machinery in Mustard Plants

Abstract: Nitric oxide (NO) acts as a gaseous diffusible plant growth regulator. It plays an important role in growth and development of plants. Therefore, in present study mustard plants were sprayed with different concentrations of sodium nitroprusside (0, 10–4 M, 10–5 M and 10–6 M), a donor of NO, at 25 days after sowing to assess different physiological parameters. The results indicate that foliar spray of SNP upregulate chlorophyll content, chlorophyll fluorescence along with gaseous exchange parameters which further boost overall photosynthetic efficiency. A gradual increase in carbon metabolism (total reducing sugars, total carbohydrate content, glucose, fructose, sucrose and starch content) was also observed in SNP-treated plants as compared to control. Nutrient status (carbon, nitrogen, phosphorus, sulfur, potassium and magnesium) of leaves also shows a significant increase. The activity of various enzymes associated with nitrogen metabolism, CO2/HCO3− homeostasis, glycolysis, Calvin cycle and Krebs cycle (nitrate reductase, carbonic anhydrase, hexokinase, rubisco, fumarase and succinate dehydrogenase) were also increased in the presence of SNP. It was also reported that O2−, H2O2 and MDA were decreased in SNP-treated samples. SNP application also upregulate antioxidative defense system by increasing the activity of antioxidant enzymes, i.e., CAT, POX and SOD. Thus, it can be concluded from the present observation that SNP proved beneficial and alter most of the parameters which ultimately improve photosynthetic efficiency in mustard plants.

Overexpression of differentially expressed AhCytb6 gene during plant-microbe interaction improves tolerance to N 2 deficit and salt stress in transgenic tobacco

Abstract: Stenotrophomonas maltophilia has plant growth-promoting potential, and interaction with Arachis hypogaea changes host-plant physiology, biochemistry, and metabolomics, which provides tolerance under the N2 starvation conditions. About 226 suppression subtractive hybridization clones were obtained from plant-microbe interaction, of which, about 62% of gene sequences were uncharacterized, whereas 23% of sequences were involved in photosynthesis. An uncharacterized SSH clone, SM409 (full-length sequence showed resemblance with Cytb6), showed about 4-fold upregulation during the interaction was transformed to tobacco for functional validation. Overexpression of the AhCytb6 gene enhanced the seed germination efficiency and plant growth under N2 deficit and salt stress conditions compared to wild-type and vector control plants. Results confirmed that transgenic lines maintained high photosynthesis and protected plants from reactive oxygen species buildup during stress conditions. Microarray-based whole-transcript expression of host plants showed that out of 272,410 genes, 8704 and 24,409 genes were significantly (p 2 up or down-regulated) under N2 starvation and salt stress conditions, respectively. The differentially expressed genes belonged to different regulatory pathways. Overall, results suggested that overexpression of AhCytb6 regulates the expression of various genes to enhance plant growth under N2 deficit and abiotic stress conditions by modulating plant physiology.

The relationship between anthocyanin accumulation and photoprotection in young leaves of two dominant tree species in subtropical forests in different seasons

Abstract: Increasing amounts of experimental evidence show that anthocyanins provide physiological protection to plants under stress. However, the difference in photoprotection mediated by anthocyanins and other photoprotective substances in different seasons is still uncertain. To determine the relationship between anthocyanin accumulation and the photoprotective effects in different seasons, Castanopsis chinensis and Acmena acuminatissima, whose anthocyanin accumulation patterns differ in different seasons, were used as materials to explain how plants adapt to different seasons; as such, their physiological and biochemical responses were analyzed. Young leaves of C. chinensis and A. acuminatissima presented different colors in the different seasons. In summer, the young leaves of C. chinensis were purplish red, while those of A. acuminatissima were light green. In winter, the young leaves of C. chinensis were light green, while those of A. acuminatissima were red. Compared with the young red leaves, the young light green leaves that did not accumulate anthocyanins had higher flavonoid and phenolics contents, total antioxidant capacity, non-photochemical quenching (NPQ), and relative membrane leakage, and a slower recovery rate in the maximum photochemical efficiency (Fv/Fm) after high-light treatment. In addition, the net photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductance (gs), and the effective quantum yield of PSII (ΦPSII) of the young leaves in winter were significantly lower than those in summer, while the activities of catalase (CAT, EC 1.11.1.6), peroxidase (POD, EC 1.11.1.7), and superoxide dismutase (SOD, EC 1.15.1.1) were significantly higher than those in summer. These data indicate that to adapt to seasonal changes anthocyanins, other antioxidative substances and antioxidative enzymes, as well as components involved in the safe dissipation of excitation energy as heat need to cooperate with one another.

Arsenic Toxicity in Soybean Plants: Impact on Chlorophyll Fluorescence, Mineral Nutrition and Phytohormones

Abstract: Arsenic (As) is naturally present in soils and groundwater in agricultural areas, mainly in the form of arsenate (AsV) and arsenite (AsIII). It can enter soybean plants and decrease their yield and growth, therefore posing a serious problem. Our aim was to evaluate its effects on physiological events closely related to plant growth and the possible signaling pathways involved. Photosynthesis related parameters, gas exchange, mineral concentration, phytohormone content, and the expression of genes related to abscisic acid (ABA) and jasmonic acid (JA), were analyzed in soybean leaves and roots exposed to AsV and AsIII. A reduction in the CO2 assimilation rate was associated with decreased stomatal conductance, transpiration rate and intercellular CO2 concentration in treated plants. The alterations observed in the photochemical phase of the photosynthesis (OJIP -test) suggest a reduction in electron transport, mainly under AsV treatment. Arsenic also induced changes in NH4+, NO3−, PO43−, Cl−, SO42− and Na+ content in roots, while the mineral status seemed to remain unchanged in leaves. Surprisingly, ABA content was significantly lower in As-treated plants and so was the expression of GmPYL1 and GmbZIP1, genes potentially involved in ABA signaling. However, treatment caused an increase in JA content and a decrease in its precursor, 12-oxo-phytodienoic acid (OPDA), which suggests that JA could play a key role in regulating the response to the metalloid. These results build on those of previous studies and contribute to elucidating the complexity of As-triggered responses in soybean.

Pretreatment with 24-Epibrassinolide Synergistically Protects Root Structures and Chloroplastic Pigments and Upregulates Antioxidant Enzymes and Biomass in Na+-Stressed Tomato Plants

Abstract: Salt stress reduces plant growth by negatively interfering with the division rate and cellular expansion, limiting the growth and development of the roots, stems, and leaves. 24-Epibrassinolide (EBR) is a molecule extracted from plant tissues and is a plant growth regulator with a high capacity to modulate tolerance to abiotic stresses. The objective of this study was to verify the possible improvements promoted by pretreatment with EBR in salt-stressed tomato plants, evaluating the variables related to root anatomy, photosynthetic pigments, antioxidant system, and biomass accumulation. The experiment comprised four treatments: two salt conditions (0 and 150 mM NaCl, described as Na+ (−) and Na+ ( +), respectively) and two concentrations of 24-epibrassinolide (0 and 100 nM EBR, described as EBR (−) and EBR ( +), respectively). EBR modulated the protection and vascularization of root structures, as demonstrated by the increases in epidermis thickness (12%) and metaxilem diameter (119%), respectively. This steroid relieved oxidative damage, which was clearly linked to elevated activities of superoxide ascorbate peroxidase (24%) and guaiacol peroxidase (31%). EBR also benefited photosynthetic pigments, reducing the degradation of chlorophylls. In addition, pretreatment with EBR favoured a higher biomass, which was due to positive effects on leaf and root tissues, including better performance of photosynthetic machinery.

Effect of Bacillus spp. and Brevibacillus sp. on the Photosynthesis and Redox Status of Solanum lycopersicum

Abstract: Plant-growth-promoting bacteria (PGPB) are gaining attention as a sustainable alternative to current agrochemicals. This study evaluated the impact of three Bacillus spp. (5PB1, 1PB1, FV46) and one Brevibacillus sp. (C9F) on the important crop tomato (Solanum lycopersicum) using the model cv. ‘MicroTom’. The effects of these isolates were assessed on (a) seedlings’ growth and vigor, and (b) adult potted plants. In potted plants, several photosynthetic parameters (chlorophylls (a and b), carotenoids and anthocyanins contents, transpiration rate, stomatal conductance, net CO2 photosynthetic rate, and intercellular CO2 concentration, and on chlorophyll fluorescence yields of light- and dark-adapted leaves)), as well as soluble sugars and starch contents, were quantified. Additionally, the effects on redox status were evaluated. While the growth of seedlings was, overall, not influenced by the strains, some effects were observed on adult plants. The Bacillus safensis FV46 stimulated the content of pigments, compared to C9F. Bacillus zhangzhouensis 5PB1 increased starch levels and was positively correlated with some parameters of the photophosphorylation and the gas exchange phases. Interestingly, Bacillus megaterium 1PB1 decreased superoxide (O2−) content, and B. safensis FV46 promoted non-enzymatic antioxidant defenses, increasing total phenol content levels. These results, conducted on a model cultivar, support the theory that these isolates differently act on tomato plant physiology, and that their activity depends on the age of the plant, and may differently influence photosynthesis. It would now be interesting to analyze the influence of these bacteria using commercial cultivars.