Effects of Pb2+ on energy distribution and photochemical activity of spinach chloroplast

Lead (Pb2+) is a well-known highly toxic element. The mechanisms of the Pb2+ toxicity are not well understood for photosynthesis. In this paper, we reported the effect of Pb2+ on light absorption, distribution and conversion of spinach chloroplast by spectroscopy, and photochemical reaction activities. Several effects of Pb2+ were observed: (1) the absorption peak intensity of chloroplast obviously decreased in red and blue region and produced optical flattering; (2) fluorescence quantum yield nearby 680 nm of chloroplast greatly declined; (3) the excitation band nearby 440 nm of chloroplast significantly descended; (4) Pb2+ treatments reduced of the rate of whole chain electron transport, photochemical activities of PSII DCPIP photoreduction and oxygen evolution, but the photoreduction activities of PSI were little changed. Together, the studies of the experiments showed that Pb2+ decreased absorption of light on spinach chloroplast and inhibited excitation energy to be absorbed by LHCII and transferred to PSII, then reduced the conversion from light energy to electron energy, and decelerated electron transport, water photolysis and oxygen evolution.