[Electron transport and photophosphorylation, coupled with photoreduction of oxygen by chloroplasts of peas, grown under different conditions of illumination]

Abstract

A comparative study of the intensity of O2 uptake, NADP+ reduction and ATP synthesis in pea chloroplasts grown upon different illumination conditions was carried out. The rates of O2 uptake in the absence of cofactors and in the presence of ferredoxin are almost identical for "dark" and "light" chloroplasts. In a medium containing oxidized NADP+ the rate of electron transport is considerably lower in the "dark" chloroplasts; the pseudocyclic transport coupled with simultaneous reduction of O2 in these chloroplasts is somewhat higher (on the average by 30%). The decrease of electron transfer to NADP+ caused by reduction of light intensity during plant growth (presumably due to the limiting step, i. e. ferredoxin--NADP+-reductase) is to some extent compensated for by a more effective utilization of O2 as an electron acceptor. This eventually results in an increase of the ATP/NADPH ratio.