Electrochemical Phenomena Associated with the “Light Reaction” in Chloroplast Thylakoids

Abstract

Some observations are reported resulting from imposed “null potential” conditions on untreated thylakoid suspensions during successive periods of illumination and after chemical and physical modifications that affect “normal” behaviour. Comparison of normal coulombic outputs puts with those obtained from thylakoids in the presence of several inhibitors of electron flow from water to the reducing side of photo-system II, and with an inhibitor of photosystem I imply that the electrons detected are derived from the decomposition of water and are transferred to the electrode from the reducing side of photosystem I. Imposing more positive or less positive conditions of potentiostatic means prior to illumination at “null potential” resulted in signifant alterations of the parameters being measured. Similar abnormal effects were noted when the thylakoid system was examined under oxygen-saturated and anaerobic conditions. The results suggest that under circumstances wherein more positive conditions exists, the photosensitisers might in their more oxidised state, being hyperactivated receptors, increase the rate of water decomposition, resulting in concurrent increase in electron release. Conditions less positive than the “null state” result in an opposite effect.