The Turnover Of D₁ Protein And The Regulation Effects Of Exogenous Progesterone In Wheat（Triticum Aestivum L.） Leaves Under High Temperature Stress

High temperature is one of the most common abiotic stresses.It induces diverse effects on plants,such as growth inhibition,oxidative damage,inactivation of photosystem Ⅱ.PS is extremely sensitive to high temperature stressⅡ.And the turnover of D₁ protein is a key step for PS Ⅱrepair cycle.Previous studies have shown that progesterone is a common steroid hormone in plants,which mitigate the damage on plants caused by the adverse effects of salt and low temperature stress.Here,the effects of high temperature on turnover of D₁ protein and stress resistance in three wheat varieties were compared.It reveals the positive correlation between the turnover rate of D₁ protein and high temperature tolerance in wheat.Using wheat AK58 as materials,the regulation effects of exogenous progesterone on the turnover rate of D₁ protein,antioxidant activity and photosynthesis capacity of PS inⅡ wheat leaves of grouting period under high temperature stress were determined.Results showed that application of progesterone increased the turnover rate of D₁ protein,decreased the oxidative damages and improved photosynthetic performance.The aim is to elucidate the protective mechanisms of progesterone on wheat leaves under high temperature stress and provide new idea for crop protection.The main results obtained through the above work are as follows: 1.Effects of high temperature on the turnover rate of D₁ protein and PSⅡfunction in three wheat varieties.Use three wheat varieties: Chinese spring（CS）,low resistance 58（AK58）and yuongong 949（YN949）as experimental materials,the results showed that high temperature stress induced lower lipid peroxidation in AK58 than YN949 and CS,which was related to different changes of SOD,CAT,POD and H2O2.Deg1,Deg2 and Fts H1/5 had higher expression in AK58 and YN949 than CS under high temperature.Under normal conditions,the expression of D₁ protein degradationrelated genes（Deg1,Deg2,Deg5,Deg8 and Fts H1/5,Fts H2/8）in AK58 were also higher,along with the high expression of the Psb A gene and the accumulation of D₁ protein.It was presumed that rapid synthesis and degradation of D₁ protein accelerated the turnover of D₁ protein and PS Ⅱdamage repair in AK58,thereby established a basis for acclimatizing high temperatures.Corresponding to this,AK58 performed better PSII photochemical efficiency（Fv/Fm,UPSII and ETR）and Photosynthetic rate（Pn）under high temperature.2.Effects of exogenous progesterone on turnover of D₁ protein in wheat leaves under high temperature stress.Compared with individual high temperature treatment,the high abundances of phosphorylated D₁ protein and expression of Psb A were observed in wheat leaves sprayed with exogenous progesterone under high temperature stress,and the expression of STN8 were increased slightly.It indicated that the phosphorylation of D₁ protein and rapid synthesis of new D₁ protein was promoted by exogenous progesterone.Exogenous progesterone promoted the expression of D₁ protein degradationrelated genes（Deg2,Deg5,Deg8,Fts H1/5 and Fts H2/8）not only under high temperature stress but also under normal conditions,but the expression of Deg1 declined.Moreover fast D₁ protein degradation favored PSII repair,which maybe reduce the PS photoinhibitionⅡ and contribute to acclimatizing high temperatures.3.Effects of exogenous progesterone on antioxidant capacity and photosynthesis in wheat leaves under high temperature stress.The activities of antioxidant enzymes（CAT,SOD,POD,APX,GR）and the content of non-enzymatic antioxidants（GSH,ASA）were distinctly increased by foliar application of progesterone under high temperature stress,meanwhile reduced the level of reactive oxygen and the content of malondialdehyde and electrolyte leakage induced by high temperature,thus alleviated the oxidative damage.A significant decrease in chlorophyll content,Fv/Fm,ФPSⅡ,ETR,q P values and increased q N values were found in wheat leaves when exposed to high temperature,but this phenomenon could be reversed by application of progesterone.Furthermore,the net photosynthetic rates（Pn）was also improved by progesterone treatment under high temperature stress.In a word,the turnover rate of D₁ protein was different in three wheat varieties under high temperature stress.Exogenous progesterone improved the photosynthetic capability of PSⅡand photosynthetic rate through increasing activities of antioxidant system,reducing cell membrane damage,promoting the turnover of D₁ protein in wheat leaves.The results of this paper can not only further enrich the theory of "thermal suppression" of photosynthesis,but also provide a scientific basis for taking measures to prevent the premature decline of photosynthesis.