Effect of water stress on the photosynthesis of flag leaf of winter wheat

Effect of water stress on the chlorophyll a fluorescence parameters of flag leaf of the wheat was studied by using OS 30 chlorophyll fluorometer. The result indicated that the chlorophyll a fluorescence parameters of flag leaf were changed obviously under water stress. The decrease of the time in ms from the opint F 0 to the point of 1/2 F v (T 1/2 ), the ratio of the variable to maximal fluorescence (F v/F m), the ratio of the variable to minimal fluorescence (F v/F 0), variable fluorescence quenching rate (ΔF v/F 0) and Rfd (ΔF v/F t) values under water stress suggested the primary light energy conversion of PSⅡ, the potential activities of PSⅡ, the potential photosynthetic activities and photosynthetic electron transport had been inhibited. Meanwhile effect of water stress on leaf water potential was discussed.