Photosynthetic Mechanism for PEG Osmotic Stress in Different Varieties of Barley

The response of photosynthetic characteristics in three barley varieties(Ganpi No.3,Xian 91-2 and Yangsimai No.3) with different drought resistance was studied by measuring chlorophyll fluorescence parameters under the condition of drought stress set with PEG6000(5 %,10 %,15 %,20 %,25 % and 30 %) in pots.The results showed that,with the increase of drought stress on the three barley varieties,the chlorophyll a,the chlorophyll b,the chlorophyll content,maximum fluorescence(Fm),maximum photochemical efficiency(Fv/Fm),effective quantum yield(PSⅡ) significantly decreased,but the initial fluorescence(F0),electron transfer rate(ETR) and photochemical quenching(qP) non-photochemical quenching coefficient(NPQ) increased.Three varieties under the treatment of low concentration PEG only maintained the steady of the photosynthetic apparatus by reducing the light energy use and improving heat dissipation,but high concentration treatment of PEG resulted in depredation of the photosynthetic apparatus.The change range of each parameter in Xian 91-2 was less than that in Ganpi No.3 and Yangsimai No.3 was less than that of Xian 91-2.