Effects Of γ-aminobutyric Acid On Inorganic Nitrogen Metabolism,sugar Metabolism And Mineral Elements Contents Of Melon Seedling Under Hypoxia Stress

In soilless culture, hypoxia stress come into appearance as a result of insufficient oxygen supply or root-cushion formation, which influences the normal growth and development of plant Now hypoxia stress has become a bottle neck of soilless culture application to large area production.Therefore, inproving the hypoxia tolerance of crops plays a vital role in soilless culture.γ-Aminobutyric acid （GABA） is a four-carbon non-protein amino acid conserved from bacteria to plants and vertebrates.In plant physiological metabolism process,GABA can regulate cytosolic pH, limit the accumulationof reactive oxygen intermediates under oxidative stress conditions,have the role of signal transduction and osmotic adjustment, and induce synthesis of ethylene ,in a variety of ways such as adversity stress adjustment.By the method of hydroponic culture,this paper studied the effects of exogenous GABAonInorganic nitrogen metabolism,sugar metabolism and mineral elements contents of melonseedling under hypoxia Stress.Impact the exogenous GABA relieve stress mechanism of hypoxia stress.Soilless culture of plants in search of relief of hypoxia stress injury and effective measures to provide a theoretical basis.The result showed that the activities of nitrate reductase （NR）, nitrite reductase （NiR） and the contents of nitrate （NO₃^--N）, nitrite （NO₂^--N）, ammonium （NH4+-N）, amino acids, total nitrogen as well as Mn, Fe, Cu significantly increased of melon seedlings under hypoxia stress, however the contents of soluble protein and K+,Ca²⁺,Mg²⁺, Zn obviously decreased, as a result the growth of seedlings was inhibited; Compared with HY stress, the contents of NO₃^--N, NO₂^--N, NH4+-N, amino acids, soluble protein and activities of NR, NiR in roots were significantly increased when melon seedlings were grown in the nutrient solution of applying GABA under hypoxia stress, meanwhile the mineral elements contents in seedlings such as total nitrogen, K+,Ca²⁺,Mg²⁺,Zn were significantly increased, but the contents of Mn, Fe, Cu were significantly decreased, which relieved the inhibition of hypoxia to roots in melon seedlings. However, exogenous GABA and sodium tungstate application aggravated the harm of hypoxia stress to melon seedlings through inhibiting NR activity and decreasing contents of NO₃^--N, NH4+-N, glutamic acid, amino acids, soluble protein, total nitrogen t in seedlings.Hypoxia stress, melon seedling roots starch content gradually reduced, leaf starchcontent increased; Blade in the whole process of starch content of increased significantly;The root system and leaf fructose, sucrose content is first after the change trend of increase reduced; Hypoxia stress, Hypoxia stress induced melon seedling roots and leaves shows for the SS, SPS, GK activity increased at first, then decreased and roots activities INV with hypoxia stress the extension of time and reduce, leaves INV activitiies first increase performance after the change trend of lower. Hypoxia stress blade sucrose acid converting enzyme （AI） and invertase activity （INV） respectively in dealing with 2-4 d, 2-6 d increased significantly,and GK root activity increased significantly ; exogenous GABA treatment improved Hypoxia stress of blade root, the content of fructose ,SPS activity, the leaves of the GK activity and reduce the seedling leaves AI activity and INV activity. Exogenous GABA processing in dealing with 2-4 d root SS activity increased significantly.Hypoxia stress stress, melon seedling leaves and roots of anaerobic respiration enzyme lactate dehydrogenase （LDH）, leaf （alcohol dehydrogenase） ADH activity increases, add after GABA reduced low oxygen stress roots and leaves melon activity and LDH leaf ADH activity, but not significant. GABA in a certain extent, to ease the low oxygen stress on the melon seedling damage.