Effects of excess iron stress on photosynthetic characteristics and chloroplast membranes in pea seedling leaves

A hydroponic experiment was employed to study the effects of excess iron on the photosynthetic characteristics and on the compositions and fluidity of chloroplast membrane in pea （Pisum sativum） seedling leaves. The results indicated that with the iron concentration increased, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr), intercellular CO2 concentration (Ci), water use efficiency (WUE) and carboxylation efficiency (CE) showed various degree of downward trends. Chlorophyll content and maximal fluorescence (Fm), the PSⅡmaximal photochemical efficiency (Fv/Fm), PSⅡpotential photochemical efficiency (Fv/Fo), photosynthetic electron transport rate (ETR)，maximum quantum yield (Yield) and photochemical quenching coefficient (qP) also declined. However, primary fluorescence (Fo) and nonphotochemical quenching coefficient (qN) increased．At the same time, content of unsaturated fatty acids and membrane fluidity of chloroplast increased, while the saturated fatty acids decreased．These results suggested that the iron stress not only caused stomatal inhibition but also destroyed the photosynthetic structure directly. Furthermore, the iron stress also resulted in inactivation of photosynthesis center, decreases of both primary capture capacity and assimilation efficiency of light energy, and increasing leaf chloroplast membrane unsaturation degree, which caused a decline in photosynthetic capacity of pea seedlings finally.