Metal-induced inhibition of photosynthetic electron transport chain of the cyanobacteriumNostoc muscorum

Abstract

This study presents information on the mechanism of inhibition of the photosynthetic electron transport of Nostoc muscorum by chromium (Cr) and lead (Pb). Photosystem II (PS II) was found to be more sensitive both to low and high concentrations of test metals used. A considerable inhibition of photosystem I (PS I) was, however, observed at high concentrations only. Although Cr‐induced inhibition of DCPIP photoreduction and lowering of chlorophyll a (Chl a) fluorescence intensity (F685) could not be reversed by artificial electron donors (diphenyl‐carbazide (DPC), NH2OH, MnCl2 and benzidine) of PS II, these electron donors did substantially reverse the Pb‐induced inhibition of DCPIP photoreduction as well as the lowering of Chl a fluorescence. Nevertheless, an increase in Chl a fluorescence at high concentrations of Pb suggested that this metal also arrests electron flow on the reducing side of the PS II reaction centre. Besides this, the suppression of fluorescence intensity of phycocyanin at low concentrations of both metals points to the involvement of phycobilisomes in the inhibition of PS II activity. The present study demonstrates that the modes of action of Cr and Pb on PS II are quite different.

Photosynthetic Responses of Energy Plant Maize under Cadmium Contamination Stress

“…Plants growing at high levels of Cd show many physiological disorders [3]. Inhibited metabolic process is related to the decline in respiration and photosynthesis, which ultimately leads to inhibition of plant growth and yield [4].…”

Heavy metal induced changes in the spectral properties ofAnacystis nidulans

“…PS2 was affected e.g. by Cr and Pb in Nostoc muscorum (Dubey et al 1986, Prasad et al 1991, Cd in Nostoc linkia (Husaini et al 1991), Cu, Cd, Zn in Anacysac nidulans (Singh and Singh 1987), Cu in Anabaena doliolum (Rai et al 1991), Cu, Zn and Cd in Chroococcus paris (Les and Walker 1984), Hg in Spirulina platensis (Murthy and Mohanty 1991). However, the data on the effect of heavy metals on light-harvesting complex, i.e.…”