Correlation of Absorbance Changes and Thylakoid Fusion with the Induction of Oxygen Evolution in Bean Leaves Greened by Brief Flashes 1

摘要

Dark-grown bean leaves (Phaseolus vulgaris) which had been greened for several days in a repetitive series of brief xenon flashes were studied during the initial induction period when O2 evolution first appears. The induction of O2 evolution requires actinic irradiation (e.g. 2 mw/cm2 of red light) and goes to completion in about 8 minutes with a half-time just under 3 minutes. Absorbance measurements on the intact leaves showed that a change of a carotenoid pigment, monitored at 505 nm, was closely correlated with the rate of O2 evolution during the induction period. Inhibitor studies, however, showed that the absorbance change persisted in the presence of a number of inhibitors which blocked O2 evolution. Electron microscopy revealed that the primary thylakoids which were unfused in the flashed leaves before induction became fused in pairs or groups of three during the 8-minute induction period. It is postulated that the 505-nm absorbance change of the carotenoid pigment is correlated more directly with the fusion process than with O2 evolution. Heat treatment (45 C for 5 min) or infiltration with 0.8 m tris, which prevented the fusion process, also prevented the absorbance change.