Effect Of Exogenous Se On The Regulation Of Growth In Tomato Seedlings Under Ca?NO₃?₂ Stress

Soil secondary salinization is a problem that must be solved in the sustainable development of modern agriculture,and the accumulation of Ca?NO₃?₂ is one of the main causes of soil salinization.Tomato is an important vegetable cultivar,but soil salinization resulted in a decrease in tomato quality and yield.Therefore,it is important to improve the Ca?NO₃?₂ tolerance of tomato.In this study,tomato cultivar "Zhongshu 4" was used as experiment material,and effects of exogenous Se on the morphological indexes,photosynthetic and fluorescence properties,antioxidant enzyme activity and the gene expression,mineral element of content and polyamine content in tomato seedlings under Ca?NO₃?₂ stress was investigated.The main results were presented as followed:1.Compared with the control,Ca?NO₃?₂ stress significantly reduced the chlorophyll a,b,total chlorophyll content and root activity of tomato seedlings,and significantly inhibited the growth of root and shoot parts.Exogenous Se increased the chlorophyll content and root activity,thus effectively alleviating the inhibition of growth on tomato seedling under Ca?NO₃?₂ stress.2.Compared with the control,Ca?NO₃?₂ stress significantly increased the contents of hydrogen peroxide?H₂O₂?,superoxide anion?O₂·^-?and malondialdehyde?MDA?in tomato seedlings,increased the activity of SOD,POD and CAT,GR and TrxR activity and AsA-GSH cycle-related enzyme activity were decreased,significantly decreased the expression levels of antioxidant enzyme-related gene,indicated that Ca?NO₃?₂ stress caused ROS accumulation and decreased of reducing power levels due to the membrane lipid peroxidation.Exogenous Se increased the expression levels of antioxidant enzyme-related gene and significantly increased the activities of antioxidant enzymes,effectively reducing the content of H₂O₂,O2·-and MDA in leaves of tomato seedlings,and decreased the levels of membrane lipid peroxidation,Thus reduce the damage caused by Ca?NO₃?₂ stress.3.Compared with the control,Ca?NO₃?₂ stress decreased the net photosynthetic rate?Pn?,transpiration rate?Tr?and stomatal conductance?Gs?,significantly increased the intercellular CO₂ concentration?Ci? of tomato leaves,and non-Stomatal limitation was the main reason of declining Photosynthesi.Moreover Ca?NO₃?₂ stress reduced the PS?photosynthesis?Fv/Fm?,actual efficiency of PS???PS??,photochemical quenching coefficient?qP?,the apparent quantum yield?AQY?,the key enzyme RCA and FBPase,as well as the expression levels of key genes in photosynthetic carbon assimilation of tomato leaves.But the Non-photochemical quenching?NPQ?and dark respiration rate?Rd?were improved.Compared with the stress treatment,exogenous Se increased the expression levels of genes and the activity of key enzymes in photosynthetic carbon assimilation,and increased the AQY,Fv/Fm,?PS?,qP,also decreased NPQ and Rd,So increased the Pn,Gs and Tr,reduced Ci.The results showed that exogenous Se could promote the photosynthesis of plants and by inducing the expression of genes in carbon assimilation and enhancing the heat dissipation to induce the growth inhibition of tomato seedlings under Ca?NO₃?₂stress.4.Compared with the control,Ca?NO₃?₂ stress increased the element contents of Ca,S,decreased the element contents of Mg,Na and P in leaves and roots,resulting in ion toxicity in tomato seedling.At the same time,the contents of free polyamine in tomato seedlings were significantly increased,and the activities of ADC,ODC,SAMDC,DAO and PAO in the synthesis and decomposition of polyamine were significantly increased.Exogenous Se effectively reduced the element contents of Ca and S,increased the element contents of Mg,Na and P in roots and leaves of plants,as well as the contents of free polyamines and polyamine synthases were significantly increased,the content of polyamine decomposing enzymes decreased,and significantly increased the expression level of related genes,the results showed that exogenous selenium decreased the toxic ions of tomato seedlings,So that the body of the ion tends to normal levels,and maintain the higher level of polyamine in the body to alleviate the growth inhibition of tomato seedling under Ca?NO₃?₂ stress.