Regulation Mechanism Of γ-Aminobutyric Acid On Nitrogen Metabolism In Maize Seedlings Under Low Nitrogen Stress

The aminobutyric acid(GABA)is a four-carbon non-protein amino acid which is widely found in eukaryotes and prokaryotes.GABA is widely used in various tissues and organs of plants.The amount of GABA in normal plants is less varied,and when the plant is subjected to high temperatures,droughts,cold damage,mechanical stimulation,etc.,the accumulation of GABA in the face of adversity,which has been more and more aroused in recent years.In this paper,two maize varieties Yuhe 988(low nitrogen and low efficiency)and Zhengdan 958(low nitrogen and high efficiency)were used as experimental materials.When three leaves were cultured in 2 mmol·1-1ca(NO3)2 Hogland nutrient solution and Ca(NO3)2 0.025 mmol·L-1 Hogland nutrient solution,0.5 mmol·L-1 GABA was applied externally to study the changes of maize plant morphology,physiology,transcriptome and metabolome under low nitrogen stress γ-Regulation mechanism of aminobutyric acid on nitrogen metabolism in maize.The main results are as follows:1.Effects of γ-aminobutyric acid on maize morphological indices under low nitrogen stress:Under low nitrogen stress,plant height,leaf area,SPAD,nitrogen balance index and shoot dry weight of yuhe 988 and Zhengdan 958 seedlings were significantly decreased,while GABA could alleviate the effects of low nitrogen stress.2.Effects of γ-aminobutyric acid on nitrogen metabolism in maize under low nitrogen stress:Nitrate reductase activity of maize seedlings decreased as a whole,and this effect was significantly exacerbated by low nitrogen stress,while GABA treatment alleviated the effects of low nitrogen stress.The activities of glutamine synthase(GS),glutamate synthase(GOGAT)and glutamate dehydrogenase(GDH)showed an overall upward trend and were sensitive to low nitrogen stress.Under low nitrogen stress,the activities of these enzymes were significantly decreased,while GABA increased the activities of these enzymes.Glutamic acid decarboxylase(GAD)and γ-aminobutyrate transaminase(GABA-T)were sensitive to low nitrogen stress and exogenous GABA.There were significant differences in the responses of different maize varieties and different organs in the same maize variety.The results showed that the endogenous GABA content in yuhe 988 leaves was significantly reduced under low nitrogen stress,while the GABA content in leaves was significantly increased to the normal level under exogenous GABA.The root GABA content in Yuhe 988 seedlings was significantly increased under low nitrogen stress.Exogenous GABA has no significant effect on this effect.Under low nitrogen stress,the content of ammonium nitrogen in leaves of Yuhe 988 and Zhengdan 958 seedlings decreased significantly,while exogenous GABA could increase the content of ammonium nitrogen in leaves.3.Effects of γ-aminobutyric acid treatment on transcriptome and metabolome of plants under low nitrogen stress:Transcriptome analysis showed that the gene ZMA00400,which controls the biosynthesis of phenylalanine,tyrosine and tryptophan,and the gene ZMA04141,which controls protein processing in endoplasmic reticulum,were down-regulated in maize seedlings under low nitrogen stress.When exogenous GABA was applied to seedlings under low nitrogen stress,Carotenoid biosynthesis--gene ZMA00906,secondary metabolite biosynthesis gene ZMA01110,benzoxazine biosynthesis gene ZMA004402,plant circadian rhythm gene ZMA04712,photosynthetic antenna protein gene ZMA00196,zeatin biosynthesis gene ZMA00908 The performance is upward.Metabolome analysis showed that the metabolites between seedlings and normal citrogen seedlings under low nitrogen stress mainly concentrated on the biosynthesis of phenylalanine,tyrosine and tryptophan,Monobactam,aminoyl-TrNA,scopolamine,piperidine and pyridine alkaloids.Adding exogenous GABA low nitrogen treatment difference between seedlings and seedlings low nitrogen metabolites mainly for vitamin B6 metabolism,ascorbic acid and hydrochloride,arachidonic acid metabolism,benzene propane linoleic acid biosynthesis and metabolism,alpha-linolenic acid metabolism,ornithine,lysine and nicotinic acid biosynthesis of alkaloids,scopolamine,piperidine biosynthesis,benzene and pyridine alkaloids Propane biosynthesis,arginine biosynthesis.