Electron donor pool of photosystem II in Tris-washed chloroplasts in a study of low temperature delayed fluorescence

Transient time courses ("induction") and the intensity of thedelayed fluorescence of chlorophyll a (measured between 0.1and 3.9 msec after a 0.9 msec excitation period) were studiedwith a phosphoroscope at temperatures between 40 and –170°Cin Tris-washed chloroplasts. Tris-washing of chloroplasts changed the temperature dependenciesof the induction and the intensity of the delayed fluorescence.From the analysis of the induction each photosystem II reactioncenter appears to be linked to a donor pool which can supplyone electron to the acceptor pool in Tris-washed chloroplasts. An artificial electron donor, diphenylcarbazide affected thedelayed fluorescence above –100°C evidence that electronsare donated to photosystem II in at least two different ways. An electron transport inhibitor, 3-(3',4'-dichlorophenyl)-l,l-dimethylurea,changed the induction of the delayed fluorescence at temperaturesabove –60°C. The temperature dependence of the electron transport in thevicinity of photosystem II was characterized from these results. (Received May 27, 1980; )