EFFECT OF EXOGENOUS γ-AMINOBUTYRIC ACID ON GROWTH AND PHYSIOLOGICAL METABOLISM IN CUCUMBER(Cucumis sativus L.) SEEDLINGS UNDER FLOODING STRESS

The effects of exogenous γ-Aminobutyric Acid on growth,soluble protein and soluble sugar contents,antioxidant enzyme activity and reactive oxygen species content in cucumber seedlings were studied under flooding stress with vermiculite and sand culture.The result showed that the growth of seedlings was inhibited,and the soluble protein content of leaves decreased,but the soluble sugar content,SOD,POD,CAT activities,O2.-production rate and MDA content obviously increased in leaves of cucumber seedlings under flooding stress.Under stem basal flooding stress,exogenous application GABA treatment enhanced the contents of soluble protein,soluble sugar and the activities of SOD,POD,CAT in leaves,while O2.-production rate and MDA contents decreased,which suggested that GABA increased the resistance to stem basal flooding of cucumber seedlings.But under whole plant flooding conditions,exogenous application GABA treatments decreased contents of protein,sugar and the activities of SOD,POD,CAT,but O2. production rate and MDA content in leaves significant increased,which manifested that GABA treatment aggravated the harm of whole plant flooding stress to cucumber seedlings.The result suggested that under different flooding degree,the effect of exogenous GABA on growth and physiological metabolism existed significant difference.