ON THE ORIGIN OF THE 35-MU-S KINETICS OF P680(-II WITH AN INTACT WATER OXIDIZING COMPLEX(.) REDUCTION IN PHOTOSYSTEM)

The origin of the '35-mu s kinetics' of P680(+.) reduction in photosys tem II (PS II) with an intact mater oxidising complex has been analyse d by comparative measurements of laser flash induced changes of the 83 0-nm absorption and the relative quantum yield of chlorophyll (Chl) fl uorescence, The latter parameter was monitored at a time resolution of 500 ns by using newly developed home built equipment [Reifarth, F,, C hristen, G, and Renger, G, (1997) Photosynth, Res. 51, 231-242]. It wa s found that: (i) the amplitudes of the unresolved ns-kinetics of both 830-nm absorption changes and the rise of fluorescence yield exhibit virtually the same period four oscillation pattern when dark adapted s amples are excited with a train of saturating laser flashes; (ii) the corresponding oscillation patterns of the normalised extent of the 35- mu s kinetics under identical excitation conditions are strikingly dif ferent with maxima after the 3rd and 5th flash for the 830-nm absorpti on changes vs. pronounced maxima after the 4th and 8th flash for the r ise of the fluorescence yield, The period four oscillations unambiguou sly show that the '35-mu s kinetics' of P680(+.) reduction are charact eristic for reactions in PS II entities with an intact water oxidising complex. However, the disparity of the oscillation patterns of (ii) i ndicates that in contrast to the ns components of P680(+.) reduction t he 35-mu s kinetics do not reflect exclusively an electron transfer fr om Y-Z to P680(+.). It is inferred that a more complex reaction takes place which comprises at least two processes: (a) P680(+.) reduction b y Y(Z )and (b) coupled and/or competing reaction(s) which give rise to additional changes of the chlorophyll fluorescence yield. (C) 1998 Fe deration of European Biochemical Societies.