Abstract
The inhibitory effect of Ni super(2+) on photosynthetic electron transport of Chlamydomonas reinhardtii was investigated by monitoring Hill activity and fluorescence. The O sub(2)-evolution which was measured, both polarographically and under flashlight conditions, decreased with increasing nickel concentrations. Nickel inactivated photosystem (PSII) activity without affecting PSI-mediated electron flow. The photoreduction of 2,6-dichlorophenol indophenol was strongly inhibited by Ni super(2+) in the broken cells of C. reinhardtii and the activity lost could not be restored by adding 1,5-diphenyl carbazide. Nickel showed no significant effect on 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) insensitive O sub(2)-production (using 2,6-dichloro-p-benzoquinone as electron acceptor). Chl a fluorescence yields at room temperature, both in the presence and absence of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea showed significant increases in response to different nickel treatments. The results indicate that nickel inhibits the electron flow on the reducing side of PSII and that its inhibition site must be located beyond the inhibition site of DBMIB.