Effects Of Exogenous Nitric Oxide On Seeds Germination And Seedlings Physiological Characteristics Of Tea(Camellia Sinensis) Under Osmotic Stress

Tea plant has a long history of cultivation in our country,which is Thermophilic and Hygrophilous,it’s poor in drought tolerence.Nitric oxide is a signaling molecule exists widely in plant and regulatesmany processesof the growth and development in plants such as seed germination,lateral root development,stomatal closure,photomorphogenesis,programmed cell death.In particular,the application of NO in improving plant stress resistance has received extensive attention.A large number of studies show that NO can improve the drought resistance of rice,wheat,corn and other crops.However the research on the perennial woody plant just like tea is less.In this paper,Longjing 43 was chosen for the experimental material,explored the effects of exogenous NO on Seed Germination and seedling growth of tea plant under osmotic stress,and the mechanism was discussed.The main results were as follows:1.Application of SNP could significantly promote the tea seeds germination and had dose effect under osmotic stress,with the increase of SNP concentration,tea seeds germination rate,vigor index,germination index and root length showed rising firstly but dropped then.Whenthe concentration of SNP was 100μmol L^-1,the germination rate,vigor index,germination index,root length reached a maximum level,The MDA,soluble sugar and proline content were lowest,suggesting that this concentration of SNP can be most effectively relieve the inhibition of germination of tea seeds under osmotic stress.The effects of application NO specific scavenger cPTIO,K₄Fe（CN）₆and NO₂^- did not alleviate the stress,so that the exogenous nitric oxide promotes the tea seeds germination under osmotic stress.2.PEG stress inhibited the normal growth of tea seedlings.The seedling biomass,relative water content were decreased as the increase of the osmotic stress,the ratio ofroot/shoot was increased gradually.The chlorophyll a,chlorophyll b,carotenoid content and chlorophyll a/b value were reduced under osmotic stress,the chlorophyll fluorescence parameters including Fv/Fm,qP,qN,ETR showed a downward trend with the increase of the concentration of PEG and theextension of time.100μmol·L^-1 SNP treatment increased the biomass,water content of the seedlings under water dificit and prevented the increase of root/shoot ratio,improved the content of chlorophyll a,chlorophyll b,carotenoid content,inhanced the Fv/FM,qP,qN,ETR.The result showed that the exogenous NO can significantly relieve the inhibition on the development of teaseedlingunder osmotic stress.3.PEG treatment increased the proline and soluble sugar content of tea seedlingsignificantly,relative electric conductivity MDA,H₂O₂ and O₂^·-increased with varying degrees,the activity of SOD、POD、CAT、APX、GR、GPX were subject to different degrees of inhibition.100μmol·L^-1 SNP treatment significantly decreased the proline and soluble sugar content,relative conductivity,MDA,H₂O₂ and O₂^·-content under PEG stress.Carotenoid,glutathione and other low molecular weightantioxidants were also increased,and the glutathione redox ratio in vivo was also higher than PEG treatment.Exogenous NO under the mild degree stress,the antioxidant enzyme activities were significantly increased,while under heavy stress,the SOD,POD,GPX activity did not change significantly.