Effects Of Exogenous α-Naphthaleneacetic Acid On Growth And Physiological Characteristics Of Soybean Under Long-Term Drought Stress After Flowering Stage

The soybean is one of important oil crops in china, an important source of high quality protein and human edible oils and fats. The root system of soybean is not developed and needs much water and is more sensitive to drought stress. In recent years, due to global climate change,drought stress happens freguently. Drought stress has become an important limited factor on yeild and quality of soybean.In this study, Nannong 99-6 (Gycine max var. Nannong99-6) and Kefeng 1 (Gycine max var. Kefeng 1) were used to study the effect of long-term drought stress on the physiological characteristics and yield of soybean at flowering stage, at the same time,and study the effecs of exogenous a-naphthaleneacetic acid (NAA) on the growth, physiological characteristics and yield of soybean at flowering stage. The result will help to elucite the resistant mechanism of a-naphthaleneacetic acid and give some new sights for drought-resistant cultivation. The result is ad follows:1. The shoot dry mass, grain yeild and yeild components were significantly decreased under long-term drought stress.The activity of SOD, POD, CAT, APX, MDHAR,GR and content of As A and GSH in both varieties were significantly increased under drought stress. Meanwhile, H2O2, MDA contents, the production rate of O2- in leaves of soybean under drought stress were significantly increased. The increasing amplitude of Nannong 99-6 was higher than Kefeng 1.The study also showed that drought stress makes the activity of sucrose synthase enzymes (SPS and SS) and sucrose decomposition enzymes(SS, INV) were significantly increased in leaves. Glucose, frucose, sucrose and soluble sugar contents were increased under drought stress, with extension of stress time, sugar content was decreased, carbonhydrate metabolism out of balance. Long-term drought stress makes the activity of NR, GS, GDH, ICDH, GO and endopeptidase and the content of NH4+-N, NO3--N were significantly increased, the content of soluble protein was decreased, and the levels of free amino acid and proline were significantly increased, with increasing drought stress, there was a downward trend. Comparison of different varieties, the Kefeng 1 of carbon and nitrogen metabolism enzymes activity more rapid response to drought than Nannong 99-6.2. a-Naphthaleneacetic acid pretreatment significantly increased shoot dry mass, grain yield and yield components in both varieties. α-Naphthaleneacetic acid pretreatment increased the activity of POD, CAT, APX, MDHAR, GPX and the ratio of AsA/DHA and GSH/GSSG, and significantly deceased the levels of MDA H2O2 and the production rate of O2-, reduce membrane lipid peroxidation level.This study also showed that a-Naphthaleneacetic acid pretreatment makes the activity of sucrose synthase enzymes (SPS and SS) and sucrose decomposition enzymes(SS, INV) were significantly increased in leaves, glucose, frucose, sucrose and soluble sugar contents were also significantly increased, with increasing stress, sugar content was decreased. Exogenous a-naphthaleneacetic acid pretreatment makes he activity of GS, GDH, ICDH and the content of NH4+-N, soluble protein, proline were significantly increased in leaves of soybean. While the content of NH4+-N, free amino acid and the activity of NR, endopeptidase, GO were significantly decreased. The effects of exogenous a-naphthaleneacetic acid pretreatment is more significantly in Kefeng 1 than Nannong 99-6.