Inhibition of photosynthetic electron transport in nostoc muscorum by ni2+and Ag+

Abstract

This paper presents the inhibition of photosynthetic electron transport chain of Nostoc muscorum by divalent Ni2+ and monovalent Ag 4. PS I (DCPIP/ASC͢MV) and PS II (H2O͢PBQ) activities were markedly inhibited by Ni21 and Ag+ in a concentration-dependent fashion but PS II was more susceptible than PS I to Ni2+. Ag+ was more toxic to PS I than PS II. The greater sensitivity of PS II to Ni2+ was further confirmed by the inhibition of DCPIP photoreduction and Chl a fluorescence. Restoration of Ag+-induced inhibition of DCPIP photoreduction and Chl a fluorescence by artificial electron donors (DPC, NH2OH, MnCl2) and their failure to restore Ni2+-induced inhibition suggests that Ni2+ inactivates PS II by causing alteration and destruction of photosynthetic membranes, but Ag+ inhibits the electron flow at the oxidizing side of PS II. Nevertheless, the suppression of the fluorescence intensity at low concentrations of both metal cations points to the involvement of phycobilisomes in the inhibition of PS II activity. © 1991, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.