Anacystis nidulans Demonstrates a Photosystem II Cation Requirement Satisfied Only by Ca2+ or Na+

Open Access
Publisher Website
Google Scholar
Abstract
Anacystis nidulans exhibits a total loss of photosystem II (PSII) activity upon incubation in a nutrient medium deficient in Ca2+ and Na+ and containing a divalent cation chelator. This loss of activity is light-dependent, which corresponds to an energy requirement. Likewise, Ca2+ efflux takes place only in cells incubated in light. The loss of PSII activity is reversible by addition of submillimolar amounts of either Ca2+ or Na+ to the external medium but not by the addition of any other cation. Restoration of lost PSII activity also requires light. Light saturation curves for partially depleted cells demonstrate both lower maximum O2 evolution rates and decreased relative quantum yields when compared to control cells. Partial electron transport reactions isolate the site of the Ca2+/Na+ effect to the reaction center itself or immediately on its oxidizing side and exclude the water-splitting complex. O2 flash yields decline during cation depletion, indicating a decrease in the number of functional PSII reaction centers, but the maximum turnover rate for still functional reaction centers does not decline. Thus, PSII of A. nidulans exhibits an all-or-none cation requirement, satisfied only by Ca2+ or Na+.

This publication has 20 references indexed in Scilit: