Study On Physiological Mechanisms For Exogenous Selenium-mediated Drought And Salt Tolerance In Tomato

Drought and salinity are important factors limiting the growth and development of plants and directly affect the yield and quality of crops.In addition to breeding salt and drought tolerant crop varieties,the application of exogenous substances to improve their drought and salt tolerance is an important way to improve the utilization of drought and saline soils.The role of selenium（Se）in enhancing plant resistance to a variety of abiotic stresses has been reported,but its mechanism remains unclear.In this study,the role and mechanism of Se in regulating drought and salt stress resistance in tomato（Solanum lycopersicum L.）was investigated.Treatment of tomato seedlings in the form of sodium selenite applied to the nutrient solution.The main findings were as follows:1.Under drought and salt stresses,tomato seedlings exhibited the symptoms of plant dwarfism and leaf wilting.The net photosynthetic rate（Pn）,transpiration rate（Tr）,stomatal conductance（Gs）,intercellular CO₂ concentration（Ci）,and water use efficiency（WUE）were significantly reduced compared to control conditions.The exogenous of selenium significantly increased the plant height and stem thickness,increased the relative water content,enhanced photosynthesis,increased net photosynthetic rate,stomatal conductance and intercellular CO₂concentration,and improved water use efficiency of the tomato seedlings,significantly alleviating the toxic symptoms caused by salt and drought stresses.It can be seen that salt and drought stress inhibited the growth of tomatoes,while selenium addition significantly enhanced photosynthesis and improved the growth of plants.2.Under drought and salt stresses,exogenous application of selenium reduced the relative conductivity,malondialdehyde,hydrogen peroxide and superoxide anion content and their accumulation in tissues,decreased the soluble sugar and proline content,and catalase（CAT）,peroxidase（POD）,and superoxide dismutase（SOD）activities in tomato seedlings.It can be seen that the addition of selenium alleviated the damage caused by drought and salt stress to tomato seedlings and mitigated oxidative damage in tomato plants,thus indirectly reducing the need for osmoregulatory substances and antioxidant enzymes in plants under stresses.3.Under drought and salt stresses,the salicylic acid（SA）content of tomato plants increased after exogenous Se application,and the expression of genes related to SA synthesis and transformation,such as PAL1,ICS,SAMT,and SABP2,was detected.The expression level of PAL1 gene increased while that of ICS gene decreased,indicating that the increase in SA content after Se application was achieved by up-regulating the PAL pathway,and the increase in SA content had further improved the resistance of the plants.4.Under drought and salt stresses,the application of SA biosynthesis inhibitor（ABT）and Se significantly decreased the growth indexes such as stem thickness and plant height,and ABT pretreatment reduced the Pn,Gs,Ci and WUE of plants and enhanced the damage of plant leaves.It can be seen that the application of SA biosynthesis inhibitor（ABT）weakened the growth promoting effect of Se on tomato growth under drought stress and salt stress.The above results showed that the exogenous application of selenium significantly enhanced photosynthesis,increased antioxidant capacity,reduced reactive oxygen species level and increased SA content in tomato,which alleviated the degree of plant stress and promoted the growth of the plant under drought and salt stress.This experiment can lay some theoretical foundation for the application of selenium fertilizer in vegetable production.