Effects of Post-Anthesis Heat Stress on Chlorophyll a Fluorescence Parameters in Flag Leaves of Strong-Gluten Winter Wheat

Heat stress after anthesis of winter wheat is one of the main natural calamities for wheat production in northern China,which results in plant senescence and decrease of grain yield.This study was carried out on the effect of heat stress on the chlorophyll a fluorescence parameters in flag leaves of strong-gluten wheat cultivar.The results indicated that heat stress deceased the chlorophyll a fluorescence parameters of flag leaf,such as Fv(variable fluorescence),Fm(maximal fluorescence),Fv/Fm,Fv/Fo(Fo is the minimal fluorescence),which indicated that primary light energy conversion and potential photosynthetic activity and electron transport of PSⅡ had been inhibited.But differences were found at different stages of grain-filling: great decrease of Fv/Fo and Fv/Fm in flag leaves occured when(or just after) treated,then adapted recovery happened,and significant decrease occured in late stage of winter wheat,which indicated serious damage of PSⅡ in flag leaves and early senescence of plant.And decrease of net photosynthetic rate(Pn) in flag leaves resulted in decrease of 1000-grain weight and grain yield.