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Wheat is one of the most important food crops in China and its production is crucial to ensure national food security.In the north of China,wheat plants often suffer from heat and high irradiation stress during grain-filling stage,leading to damage in photosynthetic apparatus and reduction of yield.Especially,the reaction center in photosystem Ⅱ(PS Ⅱ) is prone to various environmental stresses,and the extent of damage depends on the balance between injury and repair.The repair of PSⅡ needs fast turnover of D1 protein,which is the key component of PSⅡ.During the repair of PSⅡ,damaged D1 protein must be degraded and subsequently replaced by new copies quickly.It is well known that Deg1 protease plays an important role in cleavage of damaged D1 protein.However,the dynamic change in Deg1 protease under heat and high light stress is still largely unclear.In this study,we used wheat cultivar "Aikang 58" to determine the effects of heat and high light stress on Deg1 protease and D1 protein levels and PSⅡ performance and further the regulation role of salicylic acid(SA) in the repair of PSⅡ.Wheat leaves of grain-filling stage were pretreated with 0.3 mmol/L SA and distilled water(as control) respectively and then subjected to three temperature and irradiation treatments: moderate temperature and irradiation(25℃,600 μmol m-2 s-1,MTI) for 2h,high temperature and irradiation(38℃,1600 μ mol m-2 s-1,HTI) for 2h,and HTI following by 3h MTI.Fluorescence parameters were measured using a chlorophyll fluorometer.The levels of Deg1 protease and D1 protein were analyzed by western-blotting analysis.The results showed that HTI treatment resulted in degradation of Deg1 protease and D1 protein and reversible damage to PSⅡ function.Compared with control,pretreatment with SA not only retarded degradation of Deg1 protease and D1 protein,maintained higher potential photochemical efficiency(Fv/Fm),actual photochemical efficiency(ΦPSⅡ),electron transfer rate(ETR) of PSⅡ and net photosynthetic rate(Pn) of wheat leaves under HTI,but also accelerated the recovery under non stress condition.It suggests that SA could protect photosynthetic apparatus of wheat against combined stress of heat and high irradiation to some extent via maintaining the turnover of D1 protein.