The swelling and shrinking of chloroplasts during electron transport in the presence of phosphorylation uncouplers.

Abstract

Abstract Illuminated chloroplasts undergo light-scattering changes which are associated with volume changes. These changes can be greatly increased in the presence of electron transport and the increase is quantitatively related to the Hill reaction rate. Chloroplasts treated with the uncoupler atebrin (quinacrine) are capable of very high Hill reaction rates and shrink a great deal during electron transport. The shrinking is reversed rapidly if the light is turned off and even more rapidly if the electron acceptor is exhausted. Chloroplasts treated with the uncoupler methylamine are capable of even higher Hill reaction rates but such chloroplasts swell in the light and shrink again in the dark or after the electron acceptor is exhausted. Both the atebrin-stimulated shrinking and the methylamine-stimulated swelling are partially inhibited by the presence of ATP. Carbonylcyanide phenylhydrazones, like atebrin and methylamine, permit high electron-transport rates by uncoupling the Hill reaction from phosphorylation but they completely abolish the conformational changes of chloroplasts.