Studies on the delayed light emission in spinach chloroplasts. I. Nature of two phases in development of the millisecond delayed light emission during intermittent illumination

Abstract

The time course of changes in delayed light emission measured at 1.2 msec (average) after each excitation flash during intermittent illumination of spinach chloroplasts showed a complicated time-dependent change. In this time course, the existence of at least two components was found. One which developed slowly during illumination was selectively and thoroughly eliminated by addition of the uncouplers methylamine or a low concentration of carbonylcyanide 3-chlorophenylhydrazone (CCCP), or by uncoupling treatments of chloroplasts such as EDTA washing, sonic oscillation of chloroplasts and addition of a low concentration of Triton X-100. This component was found to be completely suppressed by addition of inhibitors of electron transport, 3-(4′-chlorophenyl)-1,1-dimethylurea (CMU), 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea (DCMU) and o-phenanthroline. A suspending medium of pH 6.0 was optimal for the development of the component. The other component which developed rapidly at the onset of illumination was suppressed by the inhibitors CMU, DCMU, o-phenanthroline and high concentrations of CCCP. The highest yield of this component was observed at pH 4. The mechanism of the delayed light emission was discussed on the basis of the assumption that it is ultimately excited by a reverse reaction of the electron flow through Photoreaction II. It was concluded that the former, slowly developing component of delayed light emission is related to the amounts of accumulated highenergy intermediate or state of photophosphorylation, and the latter, fast-developing component to the amounts of reduced and oxidized products formed during illumination by Photoreaction II.