Exogenous γ-Aminobutyric Acid Affects Reactive Oxygen Species Metabolism of Melon Seedlings under Hypoxia Stress

This paper investigated the effects of exogenous γ-aminobutyric acid(GABA) on reactive oxygen species(ROS) metabolism of melon seedlings 'Xiyu 1' under normoxia and hypoxia stress with hydroponics culture.Seedlings were cultured under normoxia+GABA(5 mmol·L-1),hypoxia stress,hypoxia stress+GABA(5 mmol·L-1) respectively for 0,2,4,6,8 d,and with normoxia treatment as the control.The results showed that the productive rate of O-·2,contents of H2O2 and MDA in roots and leaves were significantly increased when melon seedlings were grown in the nutrient solution under hypoxia stress.Meanwhile,the activities of SOD,POD,CAT,APX,GR and the contents of AsA,GSH were increased compared with control.Exogenous GABA application under hypoxia stress could significantly decreased the productive rate of O-·2,the contents of H2O2 and MDA of melon seedlings by increasing the activities of SOD,CAT,APX,GR and the contents of AsA,GSH.However,exogenous GABA application had less effect on ROS metabolism under normoxia condition,including significantly improved the activities of CAT,GR and the contents of AsA,GSH,significantly decreased the contents of H2O2 and MDA,but had little influence on other physiological indexes.The results suggested that exogenous GABA alleviated the harm of hypoxia stress in melon,most likely by decreasing ROS accumulation and maintaining the stability of cell membrane structure through significantly increasing antioxidant enzyme activities and antioxidant substance contents in roots and leaves of melon seedlings.