Effect Of Exogenous NADPH On Thioredoxin System And Photosynthetic Carbon Assimilation In Tomato Seedlings Under NaCl Stress

Salt stress can disorder the water uptake and metabolism function of plant cells, inhibit the normal growth of plants and decrease the yield and quality. Therefore, it is necessary to understand the mechanism of salt stress and to seek ways to increase the salt tolerance of crops. Using processing tomato variety "Liger-87-5" as the tested material, a hydroponic experiment was conducted to study the effects of exogenous different concentrations of NADPH on the thioredoxin system and photosynthetic carbon assimilation of processing tomato seedlings under Na Cl stress. The relationships between thioredoxin system and photosynthetic carbon assimilation were also explored. Main research results are as follows:1、NaCl stress caused the plant dwarf, decreased root activity and biomass, hindered moisture and nutrients absorption and translocation, and increased membrane lipid peroxidation. Exogenous spraying5,10,15 μM NADPH could improve the morphological index, increase osmotic adjustment substance concentrations and reduce the cell membrane peroxidation of processing tomato seedlings under salt stress,which effectively alleviated the Na Cl stress on the growth inhibition of tomato seedlings. And spraying 10μM NADPH had a better effect.2、NaCl stress decreased the thioredoxin reductase(TrxR) and thioredoxin peroxidase(Tpx) activity of the processing tomato seedling leaves, causing the cells state in an oxidized redox level, Na Cl stress increased the mRNA expression levels of all genes in the NTS system. NaCl stress also increased the mRNA expression levels of Trxh1, Trxh2 genes, but decreased the NTRV1 gene expression levels in the Fd/Trx system of leaves. Exogenous NADPH imroved the TrxR and Tpx activity, increased the concentrations of NADPH, GSH, AsA and the ratios of NADPH/NADP+, GSH/GSSG, AsA/DHA.Exogenous NADPH eased the damage of Na Cl stress on processing tomato seedlings by regulating the mRNA transcriptional expression of thioredoxin protein genes.3、NaCl stress increased the ROS accumulation, inhibited the antioxidant enzymes activities of processing tomato seedling leaves, and decreased the gene expression of antioxidant enzymes. Exogenous spraying NADPH improved the reducing force, increased antioxidant enzyme activities and the key antioxidant enzyme gene expression levels of processing tomato seedling leaves, reduced toxic effect caused by oxidative stress and ensured the normal physiological metabolism of processing tomato seedlings.4、NaCl stress led to the light damage and photoinhibition of tomato leaves, reduced Pn value, the total and initial activity of Rubisco, and the expression levels of key genes of photosynthetic carbon assimilation. NaCl stress inhibited the photosynthesis of processing tomato seedlings and reduced the accumulation of photosynthetic products. Exogenous spraying NADPH improved the PSII photochemical reaction and Rubisco activity, up-regulated the key genes expression of photosynthetic carbon assimilation,improved Pn significantly, which alleviated the NaCl stress on photosynthetic reaction inhibition.