Regulating Effects of Exogenous Spermidine on Photosynthetic Character and Antioxidant Metabolism of Soybean Seedling Leaves under Salt Stress

In order to explore the mechanism that spermidine( Spd) improves soybean seedlings resistance to salt stress,takeing Zhengdou 30 as material,we studied the effects of Spd with different concentration on photosynthetic character and antioxidant metabolism of soybean seedling leaves under salt stress( 100 mmol·L~(-1)Na Cl). The results are as follows: under salt stress,the relative drought matter increase rate( RDMTR),the activity of antioxidant enzymes( superoxide dismutase: SOD,peroxidase: POD,catalase: CAT,and ascorbic acid oxidase : APX) and photosynthetic parameters( net photosynthetic rate:Pn,stomatal conductance: Gs,intercellular CO_2concentration: Ci,transpiration rate: Tr) of soybean seedling leaves significantly decreased,however,relative electrolyte leakage rate( RELR),superoxide anion generation rate( O~-_2·),hydrogen peroxide( H_2O_2) and malondialdehyde( MDA) contents increased. But,exogenous Spd with different concentration increased RDMIR,the activity of antioxidant enzymes and photosynthetic parameters of soybean seedling leaves and decreased RELR,O~-_2·,H_2O_2 and MDA contents,and the increases or decreases are markedly at 0. 5mmol·L~(-1)Spd concentration. These results suggest that the appropriate concentration of Spd could decrease O~-_2· generation rate and the contents of H_2O_2 and MDA via increasing the activities of antioxidant enzymes in soybean seedlings and increase photosynthetic efficiency via improving photosynthetic parameters to alleviate the injury of salt stress to soybean seedlings and promote the growth of soybean seedlings.