Abstract
Photosystem I (PSI) cyclic electron transport is essential for photosynthesis and photoprotection. In angiosperm, the PGR5 (PROTON GRADIENT REGULATION 5)-dependent pathway is the main route of electrons in cyclic electron transport and contributes to ATP synthesis.
Previously, we reported that overaccumulation of PGR5 accelerated the rate of PSI cyclic electron transport, resulting in delayed chloroplast development. Enhanced PSI cyclic activity may cause higher reduction of the plastoquinone (PQ) pool, disturbing chloroplast development. The Arabidopsis immutans mutant, which is defective in plastid terminal oxidase (PTOX), exhibits leaf variegation, probably because of a lack of oxidized PQ supply to phytoene desaturase involved in carotenoid biosynthesis during chloroplast development. These results imply the link of the pheonotypes between PSI cyclic electron transport and PTOX. Here, we discuss the function of these alternative electron transport pathways, which were clarified from our genetic analysis.
