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A guide to environmental fluctuations that examines photosynthesis under both controlled and stressed conditions Photosynthesis, Productivity and Environmental Stress is a much-needed guide that explores the topics related to photosynthesis (both terrestrial and aquatic) and puts the focus on the basic effect of environmental fluctuations. The authors—noted experts on the topic—discuss photosynthesisunder both controlled and stressed conditions and review new techniques for mitigating stressors including methods such as transgeneics, proteomics, genomics, ionomics, metabolomics, micromics, and more. In order to feed our burgeoning world population, it is vital that we must increase food production. Photosynthesis is directly related to plant growth and crop production and any fluctuation in the photosynthetic activity imposes great threat to crop productivity. Due to the environmental fluctuations plants are often exposed to the different environmental stresses that cause decreased photosynthetic rate and problems in the plant growth and development. This important book addresses this topic and: * Covers topics related to terrestrial and aquatic photosynthesis * Highlights the basic effect of environmental fluctuations * Explores common stressors such as drought, salinity, alkalinity, temperature, UV-radiations, oxygen deficiency, and more * Contains methods and techniques for improving photosynthetic efficiency for greater crop yield Written for biologists and environmentalists, Photosynthesis, Productivity and Environmental Stress offers an overview of the stressors affecting photosynthesis and includes possible solutions for improved crop production.

Mung bean is an important pulse crop. It is highly nutritive but is vulnerable to salinity stress. Therefore, the present study was aimed to investigate the protective effect of silicon (Si) against salt stress-induced damage to mung bean plants. Mung bean plants treated with NaCl (0, 50 and 100 mM) showed considerable declines in length and dry weights of shoots and roots. Chlorophyll-a (chl-a), chl-b, total chl, carotenoids and leaf relative water content (LRWC) decreased under NaCl stress. However, supplementation with Si in the form of sodium silicate (Na2SiO3) to NaCl-stressed plants ameliorated the adverse effects of NaCl on growth, biomass, pigment synthesis and leaf relative water content (LRWC). Silicon (Si)-supplemented plants exhibited enhanced chl-fluorescence and gas exchange parameters under normal (non-stress) as well as NaCl stress conditions. Salt-induced decline in the frequency of stomata and number of leaves per plant under salt stress was significantly recovered with Si supplementation. In addition, application of Si increased the levels of proline and glycine betaine in mung bean plants. Furthermore, histochemical staining tests showed that the levels of superoxide radicals and H2O2 increased with NaCl treatments, which thereby resulted in increased lipid peroxidation (LPO) and electrolyte leakage. Contrarily, decreased levels of H2O2, lipid peroxidation (measured as MDA content), and electrolyte leakage in Si-supplemented plants under NaCl stress indicated the stress mitigating role of Si. The activities of key antioxidant enzymes (SOD, CAT, APX and GR) under NaCl stress showed an increase under the NaCl regime. However, application of Si further boosted the activities of all four antioxidant enzymes in NaCl-stressed plants. The enhanced Na+ uptake and Na+/K+ ratio in mung bean plants accompanied by decreased K+ and Ca2+ uptake under NaCl stress were reversed with Si supplementation thereby resulting in enhanced accumulation of K+ and Ca2+ and decreased Na+. In conclusion, Si supplementation mitigated the negative effects of NaCl on mung bean plants through modifications in uptake of inorganic nutrients, osmolyte production and the antioxidant defence system.

Brassinosteroids (BRs) are an important group of plant steroidal hormones that are actively involved in a myriad of key growth and developmental processes from germination to senescence. Moreover, BRs are known for their effective role in alleviation of stress-induced changes in normal metabolism via the activation of different tolerance mechanisms. Efforts to improve plant growth through exogenous application of BRs (through different modes such as foliar spray, presowing seed treatment, or through root growing medium) have gained considerable ground world over. It has been widely demonstrated that the exogenous application of BRs to stressed plants imparts the stress tolerance mechanisms. In BR-induced regulation of physio-biochemical processes in plants, interaction (crosstalk) of BRs with other phytohormones has been reported. This crosstalk may fine-tune the effective roles of other hormones in regulating stress tolerance. The multifaceted role of BRs consolidated so far has reflected their immense potential to help plants in counteracting the stress-induced changes. The effects of introgression and up- and down-regulation of BR-related genes reported so far to improve crop productivity have been presented here. Strong evidence exists that BRs are involved in signal transduction particularly in the regulation of the mitogen-activated protein kinase (MAPK) cascade, which in turn is involved in controlled development, cell death, and the perception of pathogen-associated molecular pattern (PAMP) signaling. How far BRs are involved in signal transduction pathways operative under stressful environments has also been comprehensively discussed in this review.

The present study was carried out to investigate the beneficial role of exogenous application of salicylic acid (1 mM SA) and nitric oxide (100 μM NO) in preventing the oxidative damage in Vigna angularis triggered by salinity stress. Salinity (100 mM NaCl) stress reduced growth, biomass accumulation, chlorophyll synthesis, photosynthesis, gas exchange parameters, and photochemical efficiency (Fv/Fm) significantly. Exogenous application of SA and NO was affective in enhancing these growth and photosynthetic parameters. Salinity stress reduced relative water content over control. Further, the application of SA and NO enhanced the synthesis of proline, glycine betaine, and sugars as compared to the control as well as NaCl treated plants contributing to the maintenance of tissue water content. Exogenous application of SA and NO resulted in up-regulation of the antioxidant system. Activities of enzymatic antioxidants including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), and glutathione reductase (GR), as well as the content of non-enzymatic components, were more in SA + NO treated seedlings as compared to control and salinity stressed counterparts resulting in significant alleviation of the NaCl mediated oxidative damage. Content of nitrogen, potassium, and calcium increased due to SA and NO under normal conditions and NaCl stress conditions while as Na and Cl content reduced significantly.

Pot experiments were conducted to investigate the role of selenium in alleviating cadmium stress in Solanum lycopersicum seedlings. Cadmium (150 mg L−1) treatment caused a significant reduction in growth in terms of height and biomass accumulation and affected chlorophyll pigments, gas exchange parameters, and chlorophyll fluorescence. Selenium (10 μM) application mitigated the adverse effects of cadmium on growth, chlorophyll and carotenoid contents, leaf relative water content, and other physiological attributes. Lipid peroxidation and electrolyte leakage increased because of cadmium treatment and selenium-treated plants exhibited considerable reduction because of the decreased production of hydrogen peroxide in them. Cadmium-treated plants exhibited enhanced activity of antioxidant enzymes that protected cellular structures by neutralizing reactive free radicals. Supplementation of selenium to cadmium-treated plants (Cd + Se) further enhanced the activity of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) by 19.69, 31.68, 33.14, and 54.47%, respectively. Osmolytes, including proline and glycine betaine, increased with selenium application, illustrating their role in improving the osmotic stability of S. lycopersicum under cadmium stress. More importantly, selenium application significantly reduced cadmium uptake. From these results, it is clear that application of selenium alleviates the negative effects of cadmium stress in S. lycopersicum through the modifications of osmolytes and antioxidant enzymes.

Experiments were conducted to evaluate the role of exogenously applied nitric oxide (NO; 50 µM) and spermidine (Spd; 100 µM) in alleviating the damaging effects of Ni (1 mM NiSO 4 6H 2 O) toxicity on the growth, chlorophyll metabolism, photosynthesis, and mineral content in tomato. Ni treatment significantly reduced the plant height, dry mass, and the contents of glutamate 1-semialdehyde, δ-amino levulinic acid, prototoporphyrin IX, Mg–prototoporphyrin IX, total chlorophyll, and carotenoids; however, the application of NO and Spd alleviated the decline considerably. Supplementation of NO and Spd mitigated the Ni-induced decline in photosynthesis, gas exchange, and chlorophyll fluorescence parameters. Ni caused oxidative damage, while the application of NO, Spd, and NO+Spd significantly reduced the oxidative stress parameters under normal and Ni toxicity. The application of NO and Spd enhanced the function of the antioxidant system and upregulated the activity of glyoxalase enzymes, reflecting significant reduction of the oxidative effects and methylglyoxal accumulation. Tolerance against Ni was further strengthened by the accumulation of proline and glycine betaine due to NO and Spd application. The decrease in the uptake of essential mineral elements such as N, P, K, and Mg was alleviated by NO and Spd. Hence, individual and combined supplementation of NO and Spd effectively alleviates the damaging effects of Ni on tomato.

The protective role of exogenously applied kinetin (10 μM KN, a cytokinin) against the adverse effects caused by NaCl-induced (150 mM) stress in Solanum lycopersicum was investigated. Application of KN significantly enhanced growth and biomass production of normally grown plants (non-stressed) and also mitigated the adverse effect of NaCl on stressed plants to a considerable extent. Among the examined parameters, chlorophyll and carotenoid contents, photosynthetic parameters, components of the antioxidant system (both enzymatic and non-enzymatic), osmotica accumulation, and mineral uptake exhibited a significant increase following the application of KN. Furthermore, KN application reduced the generation of reactive free radical hydrogen peroxide, coupled with a significant reduction in lipid peroxidation and an increase in membrane stability. The activities of antioxidant enzymes, and glyoxylase system were found to be promoted in plants exposed to NaCl, and the activities were further promoted by KN application, thereby protecting S. lycopersicum plants against NaCl-induced oxidative damage. Further strengthening of the antioxidant system in KN supplied plants was ascribed to regulation of ascorbate-glutathione cycle, phenols and flavonoids in them. The levels of proline and glycine betaine increased considerably in KN-treated plants, thereby maintaining relative water content. Moreover, exogenous KN application reduced the inhibitory effects of NaCl on K+ and Ca2+ uptake, which resulted in a considerable reduction in tissue Na+/K+ ratio.

Background Salinity is one of the damaging abiotic stress factor. Proper management techniques have been proposed to considerably lower the intensity of salinity on crop growth and productivity. Therefore experiments were conducted to assess the role of improved nitrogen (N) supplementation on the growth and salinity stress tolerance in wheat by analyzing the antioxidants, osmolytes and secondary metabolites. Results Salinity (100 mM NaCl) stress imparted deleterious effects on the chlorophyll and carotenoid synthesis as well as the photosynthetic efficiency. N supplementation resulted in increased photosynthetic rate, stomatal conductance and internal CO 2 concentration with effects being much obvious in seedlings treated with higher N dose. Under non-saline conditions at both N levels, protease and lipoxygenase activity reduced significantly reflecting in reduced oxidative damage. Such effects were accompanied by reduced generation of toxic radicals like hydrogen peroxide and superoxide, and lipid peroxidation in N supplemented seedlings. Antioxidant defence system was up-regulated under saline and non-saline growth conditions due to N supplementation leading to protection of major cellular processes like photosynthesis, membrane structure and function, and mineral assimilation. Increased osmolyte and secondary metabolite accumulation, and redox components in N supplemented plants regulated the ROS metabolism and NaCl tolerance by further strengthening the antioxidant mechanisms. Conclusions Findings of present study suggest that N availability regulated the salinity tolerance by reducing Na uptake and strengthening the key tolerance mechanisms.

The effects of 24-epibrassinolide (EBL, 10−6 M) on mitigation of mercury (Hg, 15 μM and 30 μM HgCl2) toxicity on growth, physio-biochemical attributes, and antioxidant enzymes in chickpea (Cicer arietinum L.) were evaluated. Mercury (Hg)-treated plants showed reduced growth and leaf pigment content in a concentration-dependent manner, but this effect was significantly ameliorated by EBL application. Exogenously applied EBL enhanced the accumulation of proline and glycine betaine (GB) in control as well as in Hg-treated plants reflecting the positive effects of EBL on leaf’s relative water content (RWC) in the plants. EBL supplementation reduced the production of hydrogen peroxide, and hence, lipid peroxidation that ultimately provided membrane stability, thereby aiding in reducing electrolyte leakage induced by Hg toxicity. Application of EBL significantly improved the activities of antioxidant enzymes including SOD, CAT, GST, and GPX, thereby resulting in optimization of the ascorbate–glutathione pathway by improving the contents of electron donors and redox components, ascorbate (AsA), and glutathione (reduced as well as oxidized), which might have contributed to protecting the photosynthetic electron transport chain from Hg-induced oxidative stress. Considerable improvement in the uptake of essential elements was also obvious in EBL-treated plants. In conclusion, Hg stress induced adverse effects on growth and development of chickpea seedlings; however, EBL-treated seedlings showed restored growth through modulation of biochemical parameters and enzymatic and nonenzymatic antioxidants.

Supplying food to an ever-increasing population is one of the biggest challenges worldwide. Environmental stresses make this situation even graver. New technological approaches are imperative. Recently, genetic engineering has contributed enormously to the development of genetically modified varieties of different crops such as cotton, maize, rice, canola and soybean. Identification of stress-responsive genes and their subsequent introgression or overexpression within sensitive crop species are now being widely carried out by plant scientists. In this review, the role of biotechnology in association with genomics and its successes, endeavours, prospects and challenges in developing stress-tolerant crop cultivars are discussed. Abstract Increasing global population, urbanization and industrialization are increasing the rate of conversion of arable land into wasteland. Supplying food to an ever-increasing population is one of the biggest challenges that agriculturalists and plant scientists are currently confronting. Environmental stresses make this situation even graver. Despite the induction of several tolerance mechanisms, sensitive plants often fail to survive under environmental extremes. New technological approaches are imperative. Conventional breeding methods have a limited potential to improve plant genomes against environmental stress. Recently, genetic engineering has contributed enormously to the development of genetically modified varieties of different crops such as cotton, maize, rice, canola and soybean. The identification of stress-responsive genes and their subsequent introgression or overexpression within sensitive crop species are now being widely carried out by plant scientists. Engineering of important tolerance pathways, like antioxidant enzymes, osmolyte accumulation, membrane-localized transporters for efficient compartmentation of deleterious ions and accumulation of essential elements and resistance against pests or pathogens is also an area that has been intensively researched. In this review, the role of biotechnology and its successes, prospects and challenges in developing stress-tolerant crop cultivars are discussed.