Thallium induces morphological changes in the photosynthetic apparatus of synechocystis sp. PCC6803

Abstract

The aim of this study was to elucidate the mechanism of thallium (Tl) ion toxicity in photosynthetic organisms. The physiological and biochemical responses to Tl exposure were analyzed in the cyanobacterium Synechocystis sp. PCC6803, which is a widely used model to study photosynthesis. We examined the photosynthetic activities of Tl+-exposed cells, the extent of Tl accumulation, and the properties of membrane lipids. Exposure to Tl+ at 2.0 and 5.0 for 24 h decreased the net photosynthetic activities of cells to 92% and 34%, respectively. After exposure to 2.5 μM Tl+, cells concentrated the Tl to 20.8 μM on a packed cell volume basis. Exposure of Synechocystis to 0–2.5 μM Tl+ resulted in an approximately 9-fold concentration factor. Treatment with 2.0 μM Tl+ for 48 h decreased the total lipid content of the cells by 38%. Further, we observed the ultrastructure of cells treated with Tl+. The cells exposed to 5 μM Tl+ for 24 h showed thylakoid membrane fragmentation and generated less-dense particles following osmium staining. During this time, the net photosynthetic oxygen evolution of the cells was reduced to 34%. These results suggest that the accumulation of Tl in cells affects the integrity of the photosynthetic apparatus.