Protective Effect Of Salicylic Acid, Abscisic Acid And Calcium Ion Against High Irradiance Stress-induced Oxidative Damage To Wheat Leaves And Influence On Photosynthesis

Wheat is the second biggest one of corps in our country, so its yield directly influences the living standard of people and the development of the economy. Unfortunately, the environmental stresses such as heat and high light were frequently encountered by wheat during grain-filling, a key period for yield and quality formation. Under the stresses, the photosynthetic system was injured, the organic nutrition was reduced, the seed development was retarded, and therefore, the yield and quality were decreased obviously. In the present paper, the protective effect of salicylic acid(SA), abscisic acid(ABA) and calcium ion against oxidative damage induced by high irradiance and influence on photosynthesis in wheat leaves were studied. The aim was to provide the reference for selection of the exogenous substance which could prevent photosynthetic apparatus from the damage caused by the high irradiance stress.The experiments were carried out on the experimental farm of Henan Agricultural University situated at suburb of Zhengzhou City . Two experiments, one in pot and the other in field, were set up with Yumai 34 as material. In the pot planting experiment, wheat leaves were pretreated with various solutions mentioned above in the grain-filling stage (20 day after anthesis). Three days later, the wheat plants in pots were brought into the laboratory and treated for 4 hours by the high irradiance provided with 1000W tungsten lamp. The radiant intensity was 1600μmol·m·^-2·s^-1 and the temperature was controlled at 30℃. After 24 hours, the physiological characteristics of flag leaves were determined. Meanwhile, the wheat plants in the field were also sprayed with the same solutions and leaf samples were taken for the measurement of physiological characteristics at the interval of three days. The main results were as follows: 1 Effect of exogenous SA, ABA and calcium ion on high irradiance stress-induced oxidative damage and photosynthesis in wheat leaves 1. 1 Effect of SA and ABAPretreatment with SA and ABA in proper concentration could effectively protect wheat leaves from oxidative damage caused by high irradiance. Therefore, higher activity of SOD and APX, lower H₂O₂, MDA and relative conductance in wheat leaves were maintained under thecondition of photo-inhibition. As a result, the increases of Fm/Fo, Fv/Fm, PS II, qP and Pn was maintained by SA treatment. Compared with control, 50 mg-kg"1 (SA1) was the most efficient in protecting leaves against oxidative damage induced by high irradiance and in improving the photosynthetic capability among the three concentrations. However, in the treatments of SA2 and S A3, the activities of SOD and APX and Fm/Fo, Fv/Fm, PS II ,qP and Pn presented the trend of decrease firstly and then increase, while the content of H2O2 , O2'", MDA, relative conductance and qNP increased firstly and then decreased. 2. 2 Effect of ABAAfter treatment with the different concentrations of ABA, compared with control, the general trend of the activities of SOD and APX and Fm/Fo, Fv/Fm, PS II, qP manifested decreasing firstly and then increasing, but the change of APX was not significantly. The contents...