TRANSIENT CHLOROPHYLL FLUORESCENCE YIELD CHANGES FROM THE ISOLATED PHOTOSYSTEM-II REACTION CENTER INDUCED BY ELECTRON-TRANSFER

It is shown that the photoaccumulation of reduced pheophytin can occur in the isolated D1/D2/cytochrome b559 photosystem II (PSII) reaction centre when Fe(II) ie used as a donor to P680+ in a way similar to tha t observed in the presence of sodium dithionite. Using Fe(II) as an el ectron donor system it has been possible to induce chlorophyll fluores cence transients from the isolated reaction centre complex when it is reconstituted with decylplastoquinone. These transients seem to reflec t classical changes in fluorescence yield of PSII which accompany the conversion of the quinone acceptor from its oxidised to its reduced st ate. In the case of the isolated complex these decylplastoquinone depe ndent changes in fluorescence yield are dominated by direct quenching by oxidised quinone and do not reflect changes in the extent of the re combination reaction between the primary radical pair, P680+ pheophyti n-.