Fluorescence Induction Studies in Isolated Chloroplasts IV. The Inhibition of Electron Transfer from Primary to Secondary Electron Carriers of PS-II at Low Temperature and by DCMU

Abstract

In previous papers (MALKIN & KOK 1966) we have shown that it is possible to estimate the concentration of electron-transport components between PS II and PS I from the phenomenon of fluorescence induction in isolated chloroplasts. Ours and similar studies by other workers have indicated the presence of relatively high concentrations of such components (about 1/20 equivalents per total chlorophyll compared to the concentration of primary reaction centers, which is about 1/500 equivalents/ chlorophyll). This large concentration of active electron transfer components (the “pool”) is shown to be composed of a small number of different kinetic species (Fig. l): 2 in our earlier papers (MALKIN

1996), and also in the model of MURATA et al (1966) and JOLIOT (1964). KOK & FORBUSH (1968) suggested a model in which the pool is essentially the reaction center but with different reaction constants. A common feature of all models is the presence of two or three consecutive steps of the photoreduction by PS-II i.e. Q in a light reaction, followed by a dark step Q^- + A → Q + A^- in model la, and similarly for models lb and lc (Fig. 1).