Abstract:

To investigate the mechanism of chitosan promoting nodulation in vegetable soybean under salt stress,the effects of exogenous chitosan on sucrose metabolism and root accumulation in vegetable soybean under NaCl stress were explored.Effects of chitosan on nodulation,the accumulation of sucrose and reducing sugar in leaves and roots,as well as sucrose metabolism-related enzyme in vegetable soybean under NaCl stress were studied by using the vegetable soybean variety Nippon Green and the fast-growing rhizobia HH103 symbiosis as the test material in an artificial climate chamber.The results showed that the number of root nodules and fresh weight of root nodules in vegetable soybean were significantly decreased under the NaCl stress(T2)(P<0.05),with an average decrease of 36.06% and 29.91% in each stress period,respectively;the sucrose content of leaves and roots was significantly increased(P<0.05),and the reducing sugar content was significantly decreased(P<0.05);and the activities of sucrose synthase(SS)and sucrose phosphate synthase(SPS)were increased,while the activities of neutral convertase(NI)and acid convertase(AI)were decreased.The number of root nodules and fresh weight of root nodules significantly increased(P<0.05),after chitosan treatment(T3)in all stress periods,with average increases of 26.87% and 25.63% of T2;the sucrose and reducing sugar contents and sucrose metabolism-related enzyme activities of leaves and roots increased significantly compared with T2(P<0.05),with average increases of 11.32%,21.32% and 10.22%,11.11%,respectively.That chitosan could promote the nodule formation of vegetable soybean by inducing the high level of sucrose metabolism in the leaves and roots under NaCl stress and accelerating the transfer of sucrose to roots,which may be one of the important reasons for chitosan to improve the nodule formation ability of vegetable soybean under NaCl stress.

Key words: Vegetable soybean, NaCl stress, Chitosan, Glucose metabolism, Nodulation