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Photosynthesis is the unique life phenomenon of green plants, andthe key to crop yield formation. The appropriate light and temperature is importantcondition for photosynthesis. Wheat is the main food crop in China and the base ofpeople’s lives, its yield is directly related to the improvement of people’s livingstandards and the development of national economy. The optimum temperature ofwheat growth is15-20℃, thedaily mean temperature higher than15℃during grainfilling period is not conducive to the development of grains. Wheat plants tend to beaffected by high light and heat stress at the late growth and development stage,causing the destruction of photosynthetic apparatus, blocking grain growth. Thispaper studied the effects of high temperature and irradiation on D1protein, Deg5protease, PS Ⅱ activity in wheat chloroplasts,photosynthetic rate, and autioxidantenzyme activities, and the regulatory effects of salicylic acid in order to furtherexplore the regulatory mechanism of PS Ⅱ andphotosynthetic apparatus under hightemperature and irradiation and provide a basis for taking contingency measures.The wheat (cv. Aikang58) was used as experiment material through field culturingand sand culturing. Field culturing was conducted on experimental farm of HenanAgricultual University with sandy loam soil, while sand culturing was conducted inlaboratory. The wheat plants in field culturing could be used at filling stage (the20thday after flowering), and the wheat plants in sandy culturing could be used atfour-leaf stage. First, wheat leaves were pretreated with water (as control) and0.1mmol/L salicylic acid (SA), and then treated with different light and temperatureconditions. The flag leaves of field culturing plants and the expended leaves of sandyculturing plants were used to determine the level of D1protein and Deg5protease,and the related physiological indicators. The main results were as follows: 1. The regulatory effects of salicylic acid on the level of D1protein and Deg5protease under high temperature and irradiationHigh temperature and irradiation caused the decline of the content of D1protein inwheat chloroplast and the expression level of Deg5protease. Compared with control,wheat leaves pretreated with0.1mmol/L SA had a higher level of D1protein andDeg5protease under high temperature and irradiation. It was suggested thatexogenous SA could alleviate the damage to Deg5protease and D1protein underhigh temperature and irradiation, and lay the foundation for the repair of PSⅡ andthe carrying out of photosynthesis.2. Effects of salicylic acid on PSⅡ function andphotosynthetic rate of wheatUnder high temperature and irradiation, the maximum photochemical efficiency(Fv/Fm) of PS Ⅱ, actual photochemical efficiency (ΦPS Ⅱ),photochemicalquenching (qP), photosynthetic electron transfer rate(ETR), net photosyntheticrate(Pn) and stomatal conductance(Gs) of wheat leaves dropped, andnon-photochemical quenching (NPQ) and initial fluorescence(Fo) increased, whichshowed that he PSII activity center and photosynthetic function was damaged.Compared with control, the pretreatment of salicylic acid could maintain higherFv/Fm, ΦPSII, qP, ETR, Pn and Gsof wheat leaves, and lower NPQ and Folevelunder high temperature and irradiation, and accelerate the recovery of the functionsunder non-stress conditions. It was suggested that exogenous SA could improve thePSII activity, enhance the photosynthetic rate, and was conducive to the developmentof the wheat grain.3. The regulatory effects of salicylic acid on activities of antioxidant enzymes andfunction of cell membranes of wheat leavesUnder high temperature and irradiation, activities of superoxide dismutase(SOD),catalase(CAT), peroxidase(POD) in wheat leaves decreased, membrane lipidperoxidation product malondialdehyde(MDA) content, osmotic adjustmentsubstance proline(Pro) content and relative electrical conductivity increased.Compared with control, activities of SOD, CAT, POD in wheat leaves pretreatedwith SA were higher, content of MDA, Pro and the relative electrical conductivitywere lower. It was suggested that exogenous SA could improve the antioxidantenzyme activities in wheat leaves, alleviate the damage to cell membrane under hightemperature and irradiation, and enhance stress resistance of wheat plants.
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