Effects Of SA,Proline,and GABA On Nitrogen Metabolism,Yield,and Quality Of Rice Under Salt Stress

Soil salinization is one of the major stress in the world to limit crop growth and yield,and it is also an important factor limiting the stable development of rice(Oryza sativa L.)production in China.Salicylic acid(SA),proline(Pro)andγ-aminobutyric acid(GABA)play an important role in plant growth and development and against stress.In this study,two contrasting rice cultivars,salt-tolerant cultivar Longdao 5(LD5)and salt-sensitive variety Mudanjiang 30(MDJ30),were used as test materials.The mathematical models between the combination of SA,Pro,GABA and the yield of rice under salt stress were established by means of quadratic general rotary unitized design.The optimal combination of SA,Pro and GABA was obtained by frequency analysis.Based on the concentration of SA,Pro and GABA in the optimal combination,the effects of single and compound agents of SA,Pro and GABA on primary N metabolism,Pro metabolism,GABA metabolism,the dry matter translocation and distribution,yield and its components,nutritional quality and taste value of rice under salt stress were studied.This study was designed to analyze the intrinsic mechanism of three exogenous substances from the perspective of nitrogen metabolism,to reveal the response pattern of nitrogen translocation and allocation of rice to exogenous substance under salt stress,to clarify the regulation effect of single and compound agents on dry matter translocation and allocation,yield and quality of rice under salt stress,and comprehensive evaluation of the impact of exogenous substance on the yield and quality.The study enriched he physiological basis of salt tolerance in rice,provided the theoretical basis for the establishment of rice salt tolerance cultivation technology system and the improvement of rice quality under abiotic stress.The main results demonstrated that:1.The recommended optimal combination obtained by frequency analysis is 0.45~0.53mmol L~-11 for SA,27.48~32.12 mmol L~-11 for Pro and 3.41~4.30 mmol L~-11 for GABA,which can improve the rice yield more than 10%under salt stress.2.Exogenous SA,Pro,GABA and their compound agents promoted the uptake,assimilation,and accumulation of nitrogen by rice under salt stress.Exogenous substance increased nitrate nitrogen content,the activities of NR,GS,and GOGAT,decreased the activity of NADH-GDH and ammonia nitrogen content in functional leaves under salt stress.The activities of GS,GOGAT,and NADH-GDH in rice grains under salt stress were enhanced by three single agents and their combinations.The regulation effect of exogenous substances on the GOT and GPT activity in functional leaves and grain were related to the genotype.Exogenous SA,Pro,and GABA significantly increased the nitrogen translocation(NT),NT conversion rate of vegetative organ(NTCRV)and NT efficiency(NTE)of stem plus sheath and/or leaf.Exogenous compounding agents increased the NT of vegetative organ,NTE of stem plus sheath in two genotypes and NTCRV of LD5 under salt stress.Exogenous Pro+GABA and SA+Pro+GABA reduced the NTE in MDJ30 leaves under salt stress.3.Exogenous substance increased the endogenous Pro content in functional leaves of rice under salt stress.The improvement effect of SA,GABA,and SA+GABA was mainly related to the increase of P5CS activity and decrease of ProDH activity.The improvement effect of Pro,SA+Pro,Pro+GABA,and SA+Pro+GABA was mainly attributed to the increased absorption of Pro by leaves,as excessive Pro feedback inhibited P5CS activity,increased ProDH activity and OAT activity at early days.The endogenous GABA content in functional leaves increased under exogenous GABA treatment but decreased under other exogenous substance.Exogenous substance inhibits the activity of GAD,a key enzyme in GABA synthesis,and accelerates GABA degradation by increasing the GABA-T activity.4.Exogenous SA,Pro,GABA and their combinations significantly increased the dry matter accumulation in aerial part of rice under salt stress.The dry matter translocation(DMT)from vegetative organ of MDJ30 under salt stress was significantly increased by exogenous substance.Exogenous SA,Pro,GABA,SA+GABA,and Pro+GABA significantly increased the DMT efficiency(DMTE),DMT conversion rate of vegetative organ(DMTCRV)of MDJ30 under salt stress.While exogenous SA,GABA,and SA+Pro+GABA significantly decreased the DMT and DMTE of stem plus sheath in LD5,and SA+Pro+GABA significantly decreased DMTCRV of LD5.The DMT from stem plus sheath and/or leaf in LD5 under salt stress was significantly increased by Pro,SA+Pro,SA+GABA,and Pro+GABA.In addition,exogenous Pro,SA+Pro,and Pro+GABA significantly increased DMTCRV of LD5,and Pro and Pro+GABA significantly increased DMTE of stem plus sheath in LD5.Exogenous SA,Pro,GABA and their combinations significantly increased the yield of rice under salt stress.The improvement effect of exogenous substance on MDJ30 was greater than that of LD5.The effects of single agent on the yield of rice under salt stress were SA>GABA>Pro.The effect of SA+GABA and Pro+GABA on the yield of rice under salt stress was great than that of any single agent,which showed a synergistic effect.While the effect of SA+Pro was related to the genotype difference in salt tolerance,and the joint application of SA and Pro synergistically increased the yield of LD5 under salt stress.The effect of compounding agents on rice yield under salt stress was SA+Pro+GABA>SA+GABA>SA+Pro>Pro+GABA.The combination between any single agent and the other two agents showed synergistic effect.5.Based on the partial least squares method,the partial regression equations for nutritional quality and taste value of rice were established(Q~2Y and R~2Y were 75.62%and 64.30%,respectively).Through the analysis of variable important for the projection(VIP),it was determined that protein content of brown and milled rice,prolamin,and globulin are the most important factors affecting the taste value of rice.Through regression coefficient analysis,nine negatively-controlled and two positive-controlled nutritional indicators affecting the taste value of brown rice were identified.Seven factors that negatively regulate the taste value of milled rice were also identified.6.The comprehensive evaluation results for nutritional quality demonstrated that exogenous GABA,SA+Pro,and Pro+GABA increased the nutritional quality of MDJ30 under salt stress,and the effect of SA+Pro was greater than GABA and Pro+GABA.This was mainly due to the fact that many nutritional indicators under the treatment of SA+Pro was greater than that of GABA and Pro+GABA,such as the protein content of brown and milled rice,globulin content,prolamin content,glutelin content,essential amino acid content,essential amino acid index(EAAI),biological valence(BV),nutritional index(NI)and score of ratio coefficient of amino acid(SRC).In addition,SA+Pro treatment increased the amino acid scores(AAS)and chemical scores(CS)of MDJ30 under salt stress and was higher than GABA treatment.Exogenous SA+GABA enhanced the nutritional quality of LD5 under salt stress,while other exogenous substances reduced the nutritional quality of LD5 under salt stress.This was mainly due to the increase of amylose and fatty acid content of brown rice,glutelin content,AAS,CS,and SRC.The comprehensive evaluation results for taste value showed that exogenous SA increased the taste value of rice under salt stress,and was higher than that of other exogenous substance.This was mainly due to the fact that the protein and fatty acid content of brown rice and the prolamin content of MDJ30 were significantly lower than that of other exogenous substance,and the ratio of glutelin to prolamin in MDJ30 significantly higher than that of other exogenous substance;and the fact that the fatty acid content of brown rice and glutelin in milled rice of LD5 significantly lower than other exogenous substance.The comprehensive evaluation results for yield and nutritional quality showed that the best treatment for MDJ30 and LD5 are exogenous SA+Pro and SA+GABA,respectively.The comprehensive evaluation results for yield and taste value showed that exogenous SA+Pro+GABA is the optimal treatment of both MDJ30 and LD5.