29] In vivo effect of calcium on photosystem II

Abstract

This chapter focuses on the in vivo effect of Calcium on Photosystem II. A Ca 2+ requirement for photosystem II (PSII) was first indicated in isolation protocols for photosynthetically active cyanobacterial membranes. In view of the extensive homology between the photosynthetic membrane structure and function of chloroplast and cyanobacterial thylakoid membranes, it is not surprising that Ca 2+ has been implicated in PSII of fractionated chloroplast membranes as well. Experiments with PSII submembrane preparations from cyanobacterial cells, however, indicate a site of function different from that observed in chloroplast PSII preparations. In cyanobacterial thylakoid membranes and PSII preparations the Ca 2+ requirement lies close to the reaction center, while in PSII preparations from chloroplasts the water-oxidizing complex demonstrates a requirement for Ca 2+ . Cyanobacteria afford the opportunity to examine PSII Ca 2+ requirement in vivo, thus eliminating possible artifacts which may develop during membrane isolation and fractionation. The chapter reports the detailed conditions which lead to Ca 2+ deficiency in intact cyanobacterial cells, and describe types of experiments that can be used to probe the function of Ca 2+ in cyanobacterial thylakoid membranes using intact, Ca 2+ -depleted cells.