Effect Of Water Stress On Photosystem Ⅱ In Two Wheat Cultivars With Different Drought Resistance

Water stress affects the plant on configuration, physiology and biochemistry and so on. Especially it damages the activity of photosystem II (PSII) in plant. The effects of osmotic dehydration on the photochemical acting, gene transcription, and protein content of PSII in leaves of two wheat (Triticum aestivum L.) cultivars Miannnong NO. 4 and NO. 5 were studied.Roots of both cultivars were submerged into polyethylene glycol (PEG) solutions with an osmotic potential of -0.5 MPa for 0, 24, 48, and 72 h. Relative water content (RWC) decreased markedly after 48 and 72 h. Simultaneously, marked increase in electrolyte leakage, decrease in contents of chlorophylls (Chl) a and b, and inhibition in PSII acting were observed.Northern hybridization indicated that progressive water stress remarkably reduced contents of the chloroplast gene psbA and psbD and nuclear gene cab transcripts. Urea-SDS-PAGE and Western blotting analysis showed that the contents of major PSII proteins', including the D1 and D2 proteins in the PSII reaction centre (RC) and the light-harvesting chlorophyll a/b-protein complex (LHCII) in periphery, declined with increasing water stress. Thus the effects of water stress on PSII major functional proteins may account for the decrease in PSII acting.Miannong NO. 5 had less destroyed plasma membranes and slower decreasesof RWC, Chi contents, and DCIP photoreduction during water stress than Miannong NO. 4, which suggested its well drought resistance. The significant difference in steady state contents of LHCII proteins of two cultivars can be mainly attributed to the marked difference in transcript level of cab gene and remarkable difference in their drought resistance, which indicated that LHCII proteins protect PSII RCs.