Effect Of Exogenous Aminobutyric Acid On Nitrogen Metabolism And Nutrition Quality Of Lettuce

In recent years, with the development of facility vegetables growing,serious consequence caused by excessive application of fertilizer, has become one of the three major sources of vegetables pollution, seriously affect on crop yield and quality, and eventually affect human health by the food chain.Lettuce widely cultivated as one of the facilities leafy vegetables,the apply fertilizer has a very close relationship with improvement of the production yield and quality of lettuce.Thus reducing the content of lettuce nitrate has important meaning in improving the yield and quality.γ-aminobutyric acid (GABA) is a four-carbon non-protein amino acid conserved from bacteria to plants and vertebrates. In recent years,research about the exogenous GABA on metabolism of plant physiology mainly focused on theimprovement of resistance of salt stress , cold stress , hypoxia stress,but few reports about exogenous GABA on the effect of the quality in vegetables.So, a hydroponics experiment investigated that the effect of exogenous GABA on nitrogen metabolism and mineral elements contents of lettuce under different nitrogen level, defined the optimum time,concentration and method for add exogenous GABA,trial to further research to investigate the effect of exogenous GABA on the nitrogen metabolism and mineral elements contents under high nitrogen stress in hydroponics culture, In order to investigate the inner mechanism of the nitrogen metabolism,provide a theoretical basis for seeking a method to reduce the nitrate content of leafy vegetables , and effective measures to improve the quality.The paper investigated that the effect of different concentration GABA on growth and quality in lettuce using three different appliction method including soaking, leaf spraying and application GABA in nutrient solution under hydroponics of non-heading lettuce variety‘Dasu’. The results showed that three application method were all promoted the growth of lettuce, decreased the nitrate content and improved the quality through increasing nitrate reductase activity.But there existed the concentration effect under different application methods, among them, the preferable concentration of soaking, leaf spraying and application GABA in nutrient solution were 5.00 mmol/L, 100 mmol/L, 2.50 mmol/L respectively.The result showed that the effect of exogenous application 2.50 mmol/LGABA in nutrient solution was best both in growth and quality improvementA hydroponics experiment was conducted to investigate the effect of exogenous application GABA time on nitrate content and quality improvement in non-heading lettuce variety‘Dasu’. The results showed that the growth and quality of lettuce were all increased under the nutrient solution applying GABA 3-12 d. And the fresh weight, activity of nitrate reductase and contents of amino acid and protein were all highest, but the the nitrate content in leaves were the lowest. While the effects of treatment 9 d and 12 d were lower than that of 6 d, and the effect of 3 d was the lowest. The results indicated that application exogenous GABA could increased yield and quality of lettuce, but there existed time effects, and the effect of 6 d was best.The lettuce variety‘Dasu’was used to investigate the effect of exogenous GABA on the growth index,nitrogen metabolism and mineral elements contents under high nitrogen stress in hydroponics culture.The results showed that compared with high nitrogen stress,the activities of nitrate reductase (NR), nitrite reductase (NiR) and the contents of nitrite (NO2--N), ammonium (NH4+-N), amino acids, soluble protein,total nitrogen as well as K+, Ca2+, Mg2+ significantly increased,however the contents of nitrate (NO3--N),Mn, Fe obviously decreased, when lettuces were grown in the nutrient solution of GABA under high nitrogen stress.However, exogenous GABA and sodium molybdate application anesis the harm of high nitrogen stress to lettuce,while exogenous GABA and sodium tungstate application had opposite effects.The result indicated that exogenous GABA might alleviate the damage of lettuce from high nitrogen stress via enhanced NR activity and improving nitrate absorption and transformation, meanwhile increased K+, Ca2+, Mg2+contents and decreased Mn, Fe contents.