Chloride involvement in the synthesis, functioning and repair of the photosynthetic apparatus in vivo

Cl- has long been known as a micronutrient for oxygenic photosynthetic resulting from its role an essential cofactor for Photosystem II (PSII). Evidence on the in vivo Cl- distribution in Spinacia oleracea leaves and chloroplasts show that sufficient Cl- is present for the involvement in PSII function, as indicated by in vitro studies on, among other organisms, S. oleracea PsII There is also sufficient Cl- to function, with K+ , of parsing the H+ electrochemical potential difference (proton motive force) across the illuminated thylakoid membrane into electrical potential difference and pH difference components. However, recent in vitro work on PSII from S. oleracea shows that oxygen evolving complex (OEC) synthesis, and re-synthesis after photodamage, requires significantly higher Cl- concentrations than satisfy the function of assembled PSII O2 evolution of the synthesised PSII with OEC. The low Cl- affinity of OEC (re-)assembly could be a component of limiting the rate of OEC (re-) assembly.