39] Acceptors and donors and chloroplast electron transport

Abstract

Publisher Summary This chapter discusses new developments in chloroplast electron-transport studies using exogenous electron acceptors and donors since 1970s. One of the notable recent developments is the introduction of a new group of Hill oxidants which are capable of intercepting electrons from photosystem II (PS-II) at very high rates even in unfragmented chloroplasts. Represented by oxidized p -phenylenediamines, these PS-II electron acceptors (or “class III acceptors”) are all lipid-soluble oxidants with high redox potentials. Together with the introduction of a number of new electron-transport inhibitors, the introduction of class III acceptors has opened up a new approach toward the mechanisms of photosynthetic electron transport and associated phosphorylation. The recognition of lipophilicity as an essential character of PS-II electron acceptors has also stimulated the interests of investigators in the membrane topology of the electron-transport system, thereby contributing much to the understanding of the structure-function of the thylakoid membrane. This chapter deals only with experiments which utilize the envelopefree “class II” chloroplasts 7 (or “type D” chloroplasts according to Hall's terminology), the standard material for electron-transport and photophosphorylation studies.