O2 supports 3-phosphoglycerate-dependent O2 evolution in chloroplasts from spinach leaves

We tested the hypothesis that the Mehler-ascorbate peroxidase (MAP) pathway supports 3-phosphoglycerate (PGA)-dependent oxygen (O-2) evolution using intact chloroplasts. Lowering O-2 concentration (<1 mu M) suppressed PGA-dependent O-2 evolution rate. High O-2 concentration (about 250 mM) enhanced the electron fluxes in Photosystem II (PSII). Also, high O-2 concentration oxidized both Q(A) in PSII and Cyt f in thylakoid membranes. These results indicated that the MAP pathway stimulated photosynthetic electron transport. Furthermore, electrochromic shift signal was also increased at high O-2 concentration, compared to low O-2 concentration. Non-photochemical quenching of chlorophyll fluorescence was also enhanced at high O-2 concentration. These data support our hypothesis that the MAP pathway functioned in intact chloroplasts and accelerated PGA-dependent O-2 evolution by inducing Delta pH formation to produce and supply adenosine triphosphate (ATP) to the conversion reaction of PGA to glyceraldehyde 3-phosphate through 1,3-diphosphoglycerate in chloroplasts.