Effects Of Tea Polyphenols On Physiological Characteristics And Antioxidant System Related Gene Expression In Wheat Under Salt Stress

Salinization is one of the most serious constraints to agriculture worldwide,especially in arid and semi-arid regions.It limits the growth and geographical distribution of plants,and adversely affects the physiological and biochemical characteristics of plants through osmotic stress,ion imbalance and toxicity.These effects include inhibiting the seed germination of plants,limiting the utilization of light energy to reduce the biomass by photosynthesis,and accelerating the production of reactive oxygen species(ROS)in cells that leads to membrane lipid peroxidation of cell membrane,which hinder the normal growth and development of plants.Therefore,it is necessary study the salt resistance mechanism of plants.In this experiment,wheat(Triticum aestivum L.)cultivar cv Longchun 30 was used as experimental material to study the effect of tea polyphenols(TP)on the physiology and gene expression of wheat under salt stress.The main research results are as follows:1.Salt treatment significantly inhibited the germination of wheat seeds,resulted in reducing biomass of wheat seedlings,as well as the root-shoot ratio,malondialdehyde(MDA),membrane tissue oxidation rate,relative electrical conductance(REC)and cell vitality loss index were significantly increased.The addition of TP effectively alleviated the inhibition of salt on the germination of wheat seeds,and had no significant effects on the biomass and root-shoot ratio of wheat seedlings,but the membrane lipid peroxidation and cell viability loss of wheat leaves were decreased.2.Salt stress significantly reduced the amount of Chlorophyll(Chl)and Chlorophyll/Carotenoid(Chl/Car)in the wheat.At the same time,it also reduced the maximum fluorescence(Fm),variable fluorescence(Fv),photosystem II(PSII)reaction center potential activity(Fv/F0),PSII electron transfer efficiency(Fm/F0),photochemical quenching(q L)and quantum yield of non-regulated energy dissipation [Y(NO)],and increased the value of initial fluorescence(F0)and non-photochemical quenching(q N),quantum yield of modulating energy dissipation [Y(NPQ)];TP alleviated the decrease of Chl content,Fm,Fv,Fv/F0,Fm/F0,q L and Y(NO)and the increase of F0,q N,and Y(NPQ)in the wheat by salt stress.3.Salt stress alone caused the accumulation of soluble protein,soluble sugar and proline(Proline,Pro)in the leaves of wheat seedlings,and the accumulation of all three was 6 d more than 3 d;In addition,ornithine transaminase(OAT),glutamate kinase(GK),pyrroline-5-carboxylic acid synthase(P5CS)and proline dehydrogenase(PDH)enzyme activities and gene expressions of OAT,P5 CS,pyrroline-5-carboxylic acid reductase(P5CR)and PDH were increased in the 1 d and 3 d wheat seeding leaves.At 6 days,GK and P5 CS enzyme activity and gene expression were raised,while OAT and PDH enzyme activities and gene expression were reduced,and the expression level of P5 CR was also decreased.The exogenous TP reduced soluble protein and soluble sugar contens caused by salt treatment,and promoted the activities of OAT,GK,P5 CS and PDH as well as the up-regulation of OAT,P5 CS,P5CR and PDH gene expression,thus further increasing Pro content in wheat leaves.4.Salt-induced resulted in hydrogen peroxide(H2O2)content increase in wheat seedling leaves,superoxide dismutase(Cu/Zn-SOD and Mn-SOD),aseorbate peroxidase(APX)and glutathione reductase(GR)gene expression levels were increased at 2 d and 4 d,while the expression of catalase(CAT)and peroxidase(POD)were enhanced only at 4d.In addition,except Cu/Zn-SOD reached the maximum at 2 d,and the expression levels of Mn-SOD,CAT,POD,APX and GR all increased first and then decreased with time and reached the maximum at 4 d.The addition of TP effectively reduced the accumulation of H2O2,Cu/Zn-SOD,Mn-SOD,CAT and POD at 4d and 6d in wheat leaves under salt stress,while APX was up-regulated at 2,4 and 6 d that increased with the extension of treatment time.GR was only down-regulated at 4 d and up-regulated at other time points.The above results indicated that salt stress significantly inhibited the germination of wheat seeds,and increased MDA content,membrane tissue oxidation rate,REC and cell viability loss of seedling leaves,resulting in cell membrance permeability increased.Chl content and Fm,Fv,Fv/F0,Fm/F0,q L and Y(NO)were reduced in leaves of seedlings,while q N and Y(NPQ)were increased,so that increased the heat dissipation of light energy,which affected the photosynthesis ability and reduced biomass accumulation of wheat seedlings.In addition,salt stress increased the soluble protein and soluble sugar contents in wheat leaves,and induced the Pro metabolic enzyme activities of OAT,GK,P5 CS and PDH,and the expression of OAT,P5 CS and P5 CR were up-regulation at 3days,the enzyme activities of GK and P5 CS and P5 CS gene expression were up-regulated,OAT,PDH activities and gene expression were decreased to increase Pro content.The up-regulation of antioxidant enzyme gene transcription level might be beneficial to remove the accumulation of H2O2 in cell and improve the salt tolerance of wheat.The addition of TP alleviated the effects of salt on seed germination,leaf membrane permeability,cell viability,Chl content and Chl fluorescence parameters,which weakened the degree of membrane peroxidation and heat dissipation and improved the photosynthetic capacity of wheat seedlings.Exogenous TP induced the enhancement of partial Pro metabolic enzymes and gene expression to promote the further increase of Pro content and decreased H2O2 under salt stress.In addition,the transcription levels of SOD,CAT and POD were down-regulated,while the transcription levels of APX and GR were up-regulated.