| In China's Huanghuai winter wheat zone, cross-stress of heat and high irradiance occurs frequently, which results in damage to photosynthetic apparatus, decline of photosynthesis in leaves, retard of seed growth and decrease in grain yield. In this paper, we studied the regulating effects of exogenous salicylic acid(SA), calcium ion (Ca2+)and nitric oxide (NO) on chloroplast protein kinase(PK), phosphorylation of D1 protein, performance of photosystemⅡ(PSⅡ), resistance to oxidative damage induced by high irradiance. The aim was to provide the reference for selection of the exogenous substance which could prevent photosynthetic apparatus from the damage caused by high temperature and irradiance stress.Using wheat variety "Yunong 949" as material, the experiments were carried out on the experimental farm of Henan Agricultual University. Wheat seeds were planted in pots and routine culturing system was adopted. Foliar sprayings of salicylic acid (SA, 0.5mmol·L-1),Ca2+(10mmol·L-1), sodium nitroprusside (SNP, 0.1mmol·L-1; which was used as NO donor) and water (as control) were done the 20th day after anthesis (grain filling stage). Then the plants were exposed to irradiance of 1800μmol·m-2·s-1 provided by 1000W tungsten lamp and temperature of 36℃. The physiological and biochemical characteristics of flag leaves were determined at 1,2,3 hours after irridance and at the stage of recovery under proper condition. The main results were as follows:1. Effects of exogenous SA, Ca2+ and NO on the content of D1 protein and the activity of protein kinases under heat and high irradiance stress in wheat leavesCross-stress of heat and high irradiance caused reversible damage to D1 protein and PSⅡfunction. The contents of D1 and D1* (phosphorylated D1 protein) decreased because of the degradation of D1. The activity of protein kinse (PK) and phosphatase declined.Pretreatment with SA, Ca2+ and NO had the distinct effects on the integrated structure of D1 protein. They all heightened the contents of D1 and D1*. Application of SA at 0.5mmol·L-1 had remarkably lifted the activity of PK, but the activity of phosphatase was remarkablrly lifted only before and after stress. Application of Ca2+ at 10mmol·L-1 had markedly lifted the activity of PK and the phosphatase. Application of SNP with 0.1mmol·L-1 had markedly lifted the activity of PK before and during stress; the activity of phosphatase was advanced before and after stress. It was concluded that Ca2+ had better effect on protecting D1 than S A and NO.2. Effects of exogenous SA, Ca2+ and NO on the function of PSⅡunder heat and high irradiance stress in wheat leavesHeat and high irradiance stress led to the lower of Fv/Fm,ΦPSⅡ, qp and electron transport rate(ETR) in PSI, PSⅡor whole chain and Pn. Spraying SA, Ca2+ and NO had effectively alleviate the damage to the function of PSⅡcaused by high temperature and irradiance stress. They all retarded the drop of Pn, Fv/Fm,ΦPSⅡ, qp, ETR, Pn.and the rise of NPQ.3. Effects of exogenous SA, Ca2+ and NO on the stress-induced oxidative damage and the stability of membrane under heat and high irradiance stress in wheat leavesCompared with control, spraying SA, Ca2+ and NO solution to leaves during grain-filling increased the antioxidant capacity of wheat leaves.Exogenous SA, Ca2+ and NO could maintain higher activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate-peroxidase (APX), reduced accumulation of H2O2,O2·and MDA content and keep lower relative permeability of cell membrane.In conclusion, it was turned out that spraying wheat plants with proper concentration of SA,Ca2+ and SNP during grain-filling could prevent the leaves from the photoinhibition induced by heat and high irradiance stress, keep higher phosphorylation level of D1 protein effectively, maintain higher activity of PSⅡ, improve photosynthetic characteristics to some extent, increase the activity of SOD,CAT and APX, decrease the content of H2O2, O2·-, relative conductance and the concentration of MDA. |
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