LIGHT-INDUCED CHANGE IN BUFFER CAPACITY OF SPINACH CHLOROPLAST SUSPENSIONS

Illumination of spinach chloroplast suspensions in the presence of a redox dye causes large changes in the buffer capacity of the suspensions. The light-induced changes of buffer capacity above pH 6.4 can be completely reversed in the dark, while buffer capacity changes at pH values less than 6.4 are partly or completely irreversible. While the light-induced buffer capacity change at pH 7.2 and light-induced net proton uptake show similar responses to uncouplers and similar light requirements, the buffer capacity change at pH 6.2 has a much lower light intensity requirement than the other phenomena. The demonstration of light-induced buffer capacity changes in chloroplast suspensions calls for quantitative reappraisal of the literature dealing with light-induced net proton uptake by chloroplasts. © 1969.