Effects of γ-aminobutyric Acid on Nitrogen Metabolism in Roots and Leaves of Cold-stressed Rice(Oryza sativa L.) During Early Vegetative Growth

Abstract:Cold stress adversely affects rice growth,particularly at the early vegetative growth stage.In higher plants,nitrogen metabolism plays a central role in amino acid metabolism,plant defense mechanisms and productivity.This report investigated the effects of cold stress and supplemental γ-aminobutyric acid （GABA） under cold stress on nitrogen metabolism in rice seedlings.Cold stress resulted in a greater increase in the transformation to NH4+by nitrate reductase （NR） in roots,it further resulted in lower levels of NO3-content in roots,weakened glutamine glutamate （GOGAT/GS） pathway and elevated glutamate dehydrogenase （GDH） pathway of rice seedlings.Whereas,compared with cold stress,supplementation of GABA (2.5 mmol·L-1) could increase relative water content（79.43%） and biomass （34.15%） of rice seedlings.GABA could act as an amplifier of stress signal conduction/transduction to increase NR activity and promote NO3-assimilation in leaves.In addition,GABA elicited the Ca2+signaling pathway which could promote the GDH pathway and GABA shunt,increase the activities of GS and GDH,and the expression of Os GAD2 and Os GDH family.The GABA might increase the ratio of the Glu family and avoid NH4+toxicity in order to raise the concentration of organic compounds and alleviate the harmful consequences of cold stress.Based on these observations,this study proposed that GABA mediated cold tolerance in rice seedlings by activating Ca2+burst and subsequent crosstalk among Ca2+signaling,GDH pathway and GABA shunt.