Effect Of Pre-Treated With NO On Salt Tolerance In Seedling And Post-Anthesis And Salt And Waterlogging And Therir Combination Effects On Effects On Grain Yield In Wheat

As key growth stages, wheat plants during germination, seedling formation and grain filling are very sensitive to salt stress.Then, it is of importance to improve seed germination and early seedling formation and tolerance during grain filling to increase grain yield in wheat under salt stress. In this study, seeds of winter wheat(Triticum aestivum L.)cultivars of Yangmai 12 and Huaima 17 were pre-soaked with 0.1 mmol L-1 of sodium nitroprusside (SNP, as nitric oxide donor) for 20 h just before germination. Effects of exogenous nitric oxide (NO) on the following seed germination and seedling growth under salt stress were studied. In addition, stresses of salt (ST) and waterlogging (WL), and their combination (SW) were imposed on wheat plants from 7 days after anthesis (DAA) in a pot culture experiment. The WL and SW treatments lasted for 5 days,while the ST treatment was continuously imposed during the grain filling stage.Effects of ST and WL stresses and SW on grain yield formation were then investigated. The main results included:1.Exogenous NO effects on seed germination and mitochondrial anti-oxidative system under by 300 mmol L-1 NaCl stress.Under this stress event, exogenous NO increased germination rate and weights of coleoptile and radicle, while reduced seed weight. Exogenous NO also enhanced seed respiration rate and ATP synthesis.Activities of amylases were then enhanced to accelerate starch degradation and total soluble sugar accumulation in germinating seeds. Meantime, exogenous NO improved degradation of protein and promoted amino acid content in seeds.Exogenous NO increased activities of superoxide dismutase (SOD) and catalase (CAT), which inhibited release of superoxide anions (O2-·) and reduced accumulation of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in seed mitochondria. Exogenous NO also reduced Na+ concentration while increased K+ concentration in the seeds, thereafter maintained a better balance between K+ and Na+ during germination under salt stress, as compared with the seeds not pretreated by SNP.2.Effects of exogenous nitric oxide on carbon and nitrogen metabolism and antioxidation system in wheat seedling under 120 mmol L-1 NaCl stress. Salt stress significantly reduced contents of chlorophyll, carotenoid, total soluble sugars and soluble protein in wheat seedlings, which resulted in a decrease of dry matter accumulation. Exogenous NO significantly reduced O2-·release rate and H2O2 content, while increased activities of SOD and CAT, which resulted in an obvious decrease in MDA content in leaves of seedlings growth under salt stress.Meanwhile, exogenous NO increased contents of chlorophyll, carotenoid, and total soluble sugars in wheat seedlings. Compared to the salt stress treatment, NO pre-treatment significantly increased soluble protein content and enhanced activities of endopeptidase and carboxypeptidase in leaves. Thus, NO effectively maintained a balance between carbon and nitrogen metabolisms in seedling growing under salt stress, and consequently resulted in a better seedling growth, and increase in plant height, fresh weight and dry weight of seedlings, compared with the non NO-pretreatment.3.Effects of salt and waterlogging and their combination on flag leaf photosynthesis, chloroplast ATP synthesis, and antioxidant capacity in wheat. In this study, rapid reductions in net photosynthetic rate (PN), stomatal conductance (GS), transpiration rate (Tr) and instantaneous water use efficiency (IWUE) in response to ST and SW treatments were observed in both cultivars, and ST and SW showed more severe adverse effects than WL. The slight decrease of PN in the WL, ST and SW treated plants was attributed mainly to the decreases of GS at 10 DAA, whereas at 18 DAA, non-stomatal limitation over PN could occur for the SW and ST treated plants. At 10 DAA, Fv/Fm,ΦpsⅡand qP did not decrease significantly, while NPQ dramatically increased under all stresses. Therefore, although the PSII was not essentially damaged under the stresses, great portion of the harvested energy by PSII was dispersed via the non-photochemical approach under stresses than under control at 10 DAA. However, at 18 DAA,ΦpsⅡ, Fv/Fm and qP were significantly lowered while NPQ was significantly increased in the ST and SW plants in relation to the CT and the WL plants, indicating ST and SW treatments led to clear damage to the PSII. It was notable that a single WL stress also obviously reduced leaf PN compared with the CT. However, this decrease of PN was seemingly not due to damage of the PSII function but to the lowered chlorophyll content and increased NPQ. In the present study, significant increases in H2O2 content and release rate of O2-·as well as MDA content in chloroplasts were observed under the ST and SW treatments. Reduction in ATP synthesis owed to depress activities of Mg2+-ATPase and Ca2+-ATPase in chloroplast under ST and SW. The adverse effects of WL was much less than that of ST and SW.4.Effects of salt and waterlogging stresses and their combination on carbon and nitrogen metabolism and balance between Na+ and K+. ST and SW treatments significantly reduced contents of soluble sugars, sucrose in the vegetative organs and grains and fructan in stem and sheath. However, ST and SW treatments increased free amino acid contents in flag leaf and others leaves, while reduced free amino acid contents in the vegetative organs and grains, which led to reduction of C/N. Contents of soluble sugar and sucrose and free amino acid in the vegetative organs and grains were slightly depressed under WL stress, which resulted in less ratio of C/N in all organs of both cultivars. ST and SW also enhanced accumulation of Na+while depressed accumulation of K+, thus resulted in a reduced K+/Na+ in wheat plants.5.Effects of salt and waterlogging stresses and their combination on wheat yield and quality. It was found that WL, ST and SW treatments significantly reduced redistribution of pre-anthesis stored nitrogen (remobilization of assimilates stored pre-anthesis), amounts of post-anthsis accumulated nitrogen (transportation of post-anthesis assimilates) transferred into grain, resulting in obviously decreasing grain yield, protein and starch yields, especially for the ST and SW treatments. Both ST and SW treatments significantly decreased grain protein accumulation and starch components.Accumulations of both cultivars grain protein and starch were significantly reduced under WL stress.In summary, exogenesis NO increased seed respiration rate and activities of amylase and consequently promoted the conversion from starch and protein into sugars and free amino acid contents. NO also increased activities of antioxidant enzymes and thus reduced oxidants (reduction in H2O2 content and O2-·release rate) in mitochondria, and facilitated a better ion balance between Na+ and K+ in seed during germination under high salinity. In addition, exogenous NO significantly reduced O2-·release rate and H2O2 content, while increased activities of SOD, CAT and endopeptidase and carboxypeptidase, which resulted in an obvious decrease of MDA content in leaves of seedlings growing under salt stress. Meanwhile, exogenous NO maintained higher contents of chlorophyll, carotenoid, and total soluble sugars in wheat seedlings. Thereby, NO effectively maintained a balance between carbon and nitrogen metabolisms in seeding growing under salt stress, and consequently resulted in a better seedling growth.Salt and waterlogging stresses and their combination reduced photosynthesis of both cultivars, depressed carbon and nitrogen metabolism, and led to an imbalance between K+ and Na+ in wheat plants.Plant senescence was then predated and duration of grain filling was shortened. Finally, both grain yield and quality were affected by these stresses.The adversary effects on yield and quality in wheat were severer under salt and combination of salt and waterloging than the single waterlogging in this study.