Thermal uncoupling in chloroplasts. Inhibition of photophosphorylation without depression of light-induced pH change

Abstract

When chloroplasts are heated at about 50 °C for 30–60 sec (or for longer periods at slightly lower temperatures) they lose much of their ability to support photophosphorylation, but electron transport and proton fluxes are accelerated and the lightinduced pH shift is maintained or even increased. It is suggested that the heat treatment increases the permeability of the thylakoid membrane to charge compensating ions so that the light-induced charge separation is diminished and that in these circumstances the generation of a proton gradient is, in itself, insufficient to promote photophosphorylation or to limit electron transport to the extent observed in untreated chloroplasts.