Role of Signaling Molecules Sodium Nitroprusside and Arginine in Alleviating Salt-Induced Oxidative Stress in Wheat.

Nitric oxide (NO) is a well-accepted signaling molecule that has regulatory effects on plants under various stresses. Salinity is a major issue that adversely affects plant growth and productivity. The current study was carried out to investigate changes in the growth, biochemical parameters, and yield of wheat plants in response to NO donors, namely sodium nitroprusside (SNP) (2.5 and 5.0 mM) and arginine (10 and 20 mM), under two salinity levels (1.2 mM and 85.5 mM NaCl). Salinity stress significantly decreased the lengths and weights of plant parts (shoot, tiller, and root) and reduced the flag leaf area, photosynthetic pigments, indole acetic acid (IAA), and yield and its components. Moreover, salt stress induced a significant accumulation of some osmoprotectants (total soluble sugars (TSS) and amino acids, especially proline) and triggered the accumulation of hydrogen peroxide (H2O2) and lipid peroxidation in wheat leaves. In contrast, arginine and SNP treatments significantly mitigated the negative impacts of salinity on growth and productivity via enhancing photosynthetic pigments, nitrate reductase, phenolic compounds, IAA, TSS, free amino acids, and proline. In addition, SNP and arginine potentially reduced oxidative damage by decreasing H2O2 and lipid peroxidation through the induction of antioxidant enzymes. The individual amino acid composition of wheat grains under the interactive effect of salinity and NO sources has been scarcely documented until now. In this study, the NO sources restrained the reduction in essential amino acids (isoleucine and lysine) of wheat grains under salinity stress and further stimulated the contents of non-essential and total aromatic amino acids. Interestingly, the applied protectants recovered the decrease in arginine and serine induced by salinity stress. Thus, SNP or arginine at the levels of 5.0 and 20 mM, respectively, had a profound effect on modulating the salt stress of wheat throughout the life cycle.

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

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.

Nano-Zinc Oxide and Arbuscular mycorrhiza Effects on Physiological and Biochemical Aspects of Wheat Cultivars under Saline Conditions.

BACKGROUND AND OBJECTIVE: Saline soils are restrictive factors to agriculture in arid and semi-arid regions, plant growth and productivity. Thus, it was important to consider how, nano-zinc oxide or bulk zinc oxide alleviates the oxidative salt stress in the presence of Arbuscular mycorrhiza (AM) fungi by two wheat cultivars (Sids 13 and Sakha 94). MATERIALS AND METHODS: A field experiment was carried out during two winter successive seasons to study the beneficial role of nano-zinc oxide or bulk zinc oxide with different concentrations (5 and 10 mg L-1) in enhancing growth, some biochemical and physiological of two wheat cultivars under saline soil. RESULTS: Soaking both wheat cultivars with nano-zinc oxide or bulk zinc oxide in the presence of AM improved growth parameters. All treatments increased significantly photosynthetic pigments, IAA, phenols contents, organic antioxidant enzyme activities and significant decrease in lipid peroxidation. some changes are observed in protein patterns, so several proteins were disappear, but others were selectively improved and synthesis of the new groups of protein was formed, some of these responses were observed through the effect of nano-zinc oxide or bulk zinc oxide and AM. CONCLUSION: Nano-ZnO (10 mg L-1) in the presence of AM was the most effective treatments on both cultivars. Results showed superiority of Sakha 94 cultivar in most growth parameters and biochemical aspects than Sids 13 cultivar.

Alleviation of drought stress by melatonin foliar treatment on two flax varieties under sandy soil.

The role of melatonin treatments on improving plant tolerance against drought stress is clear, while its special role and influences are poorly investigated. Thus, the effect of external treatment with different concentrations (2.5, 5.0 and 7.5 mM) of melatonin on two varieties of flax plant (Letwania-9 and Sakha-2) growth, some biochemical aspects and yield under normal [100% water irrigation requirements (WIR)] and drought stress conditions (75% and 50% WIR) in sandy soil were investigated in this study. Drought stress decreased significantly different growth parameters, photosynthetic pigments, yield and yield components of the two studied flax varieties. While, it increased significantly phenolic contents, total soluble sugars (TSS), proline and free amino acids as well as some antioxidant enzymes (superoxide dismutase, catalase, peroxidase and polyphenol oxidase). Meanwhile, external treatment of melatonin (2.5, 5.0 and 7.5 mM) increased significantly different growth and yield parameters as well as the studied biochemical and physiological aspects under 100% WIR. Also, melatonin treatment could alleviate the adverse effects of drought stress and increased significantly growth parameters, yield and quality of the two varieties of flax plant via improving photosynthetic pigments, indole acetic acid, phenolic, TSS, proline free amino acids contents and antioxidant enzyme systems, as compared with their corresponding untreated controls. Foliar treatment of 5.0 mM melatonin showed the greatest growth, the studied biochemical aspects and yield quantity and quality of Letwania-9 and Sakha-2 varieties of flax plants either at normal irrigation or under stress conditions. Finally we can conclude that, melatonin treatment improved and alleviated the reduced effect of drought stress on growth and yield of two flax varieties through enhancing photosynthetic pigment, osmoptrotectants and antioxidant enzyme systems. 5 mM was the most effective concentration.