US EPA

4971593 

Technical Report 

Comparison of toxic effects of mercury, copper and zinc on photosystem II of barley chloroplasts 

Chun, HS; Kwon, YM; Lee, CB 

1993 

36 

3 

195-201 

Korean 

BIOSIS COPYRIGHT: BIOL ABS. The room temperature fluorescence induction of chloroplasts was utilized as a probe to locate the site of inhibition by mercury, copper and zinc on PS II by mercury. Inhibitory effect of Hg2+ on electron transport activity was notable as compared with Cu2+ and Zn2+. At concentrations of HgCl2 over 50 muM, activities of PS II and whole-chain electron transport decreased more than 70%, while that of PS I decreased about 10 30%. This suggests a that PS II is more susceptible to Hg2+ than PS I is. In the presence of diphenylcarbazide (DPC), 50 muM HgCl2 inhibited the reduction of dichlorophenolindophenol (DCPIP) about 50%. Addition of heavy metals induced marked decrease in maximal variable fluorescence/initial fluorescence ((Fv)mo), but no changes in Fo. With various concentrations of heavy metals, changes of chlorophyll a fluorescence emitted by PS II showed gradual decrease in photochemical quenching (qQ), which indicates an increase in reduced state of electron accepto