Effects Of Exogenous Spermidine On Carbon And Nitrogen Metabolism Mechanism In Tomato Seedlings Under High Temperature Stress

High temperature is one of the major abiotic factors to influence global agricultural production.High temperature directly affects the physiological and biochemical processes in plants,and indirectly alters the growth patterns of plants.Continuous high temperature stress affects seedlings morphogenesis.Tomato(Lycopersicon esculentum Miller)is one of the main vegetable crops in the world,and is also an important model patterns in evolution and physiological research.Tomatoes are one of the major vegetable crops,in spring,summer and autumn greenhouse planting,it is vulnerable to high temperature stress.Polyamines(PAs)are kinds of low molecular and polycation in plants metabolism process,which are widely exists in plants,mainly including putrescine(Put),spermidine(Spd)and spermine(Spm).Recently,more and more researches were focused on the abiotic and biotic stress which used exogenous PAs to regulate and ease high temperature damage.And the information between PAs and high temperature stress in plant physiology is very limited,Especially metabonomics research.In the present study,we used high temperature sensitive tomato(cv.Puhong 968)as the material,through using 1 mM exogenous Spd foliar spray,we determined the effects of high temperature stress(38/28?,day/night)on tomato seedlings growth and carbon-nitrogen metabolism.We also investigated on changes of metabolites and mRNA transcription level in tomato seedlings to the molecular mechanism why exogenous Spd improved the heat resitance of tomato seedlings.The main results are as follows:1.High temperature stress significantly inhibited the growth of tomato seedlings.Under high temperature stress,tomato seedlings diameter,height,above-and under-fresh weight were significantly reduced,and the level of ROS(including O2·and H2O2)significantly increased.Exogenous Spd processing alleviated plants growth inhibition,improved the plants aboveground fresh weight,improved the biomass accumulation,and alleviated the harmful effects caused by reactive oxygen species.Under high temperature stress,the three states of Put were reduced,free and conjugated Spd were increased.Spraying Spd promoted free and conjugated Put and Spd and also down-regulated the PAO and SAMDC gene expression.Thus,mutual transformation in Put,Spd and Spm may be adapted seedlings to resist high temperature damage,high levels of endogenous Spd may be the internal causes of tomato heat resistance.2.High temperature stress increased the contents of trehalose,inositol,galactose glycosides and raffinose,and reduced the glycolysis and TCA cycle metabolites,which accelerated carbon starvation and the lack of energy supply of the seedlings,so as to inhibited the growth of plants.Spraying exogenous Spd reduced the contents of the osmotic substances,and accumulated amounts of glucose-6-phosphate,fructose-6-phosphorate,pyruvate and citrate,thereby promoted the metabolic process of glycolysis and TCA cycle,reduced the inhibition of high temperature on plant growth.High temperature significantly increased the contents of glycine,phenylalanine,tryptophan and tyrosine,Spd inhibited the effect of the high temperature of protein degradation,reduced the contents of amino acids.In addition,the exogenous Spd can greatly increase glycolysis and TCA cycle key enzyme gene expression levels.The Spd may alleviate the harmful effects of high temperature on tomato seedlings by increasing carbon metabolism and biosynthesis of amino acids.3.Under high temperature stress,the sucrose contents in tomato leaves increased significantly,fructose,glucose and starch contents were significantly reduced,the sucrose,fructose,glucose and starch in roots were significantly reduced.Spraying exogenous Spd under high temperature significantly decreased sucrose in leaves,compared with high temperature,fructose,glucose and starch increased significantly.High temperature significantly reduced the activities of key enzymes and gene expression,sucrose metabolism significantly increased after spraying Spd,SPS,SS,and AI activities and their gene expressions in leaves significantly increased.These shows that spraying exogenous Spd made tomato seedlings have better ability of sucrose metabolism,which could increased the heat resistance of tomato seedlings.4.Under high temperature stress,the contents of NO3--N in the leaves and roots of tomato seedlings significantly reduced,and NH4+-N increased significantly.Spraying Spd promoted the contents of NO3--N,reduced the NH4+-N contents.For nitrogen metabolism related enzymes,the high temperature significantly inhibited the NR,GS and GDH activities,decreased the activities of transaminase GPT and GOT.While spraying Spd promoted the key enzyme activities,and raised their gene expression,and promoted the activity of transaminase GOT and GPT,promoted the transfer process of ammonia.Under high temperature stress,spraying exogenous Spd seedlings have a stronger ability to grow,may be due to exogenous Spd up-regulated the nitrogen assimilation capacity of plants,promoted the metabolism of NH4+-N.