FLUOROMETRIC EQUIPMENT FOR MONITORING P680(-DOT) REDUCTION IN PS-II PREPARATIONS AND GREEN LEAVES(CENTER)

Newly developed equipment is described that permits the monitoring of laser flash induced transients of the normalised chlorophyll-a fluores cence quantum yield in isolated PS II preparations and whole leaves wi th a high time resolution. The essential operational unit of the set-u p is a rapidly gated photomultiplier. In this way, the fluorescence ar tefact, due to the high intensity excitation laser flash, is sufficien tly suppressed and the dead time of the signal response is reduced to about 500 ns. It is shown that the fluorescence rise kinetics in the m u\s time-domain, after flash excitation is strongly dependent on the r edox state of the primary electron donor of PS II (P680). At high exci tation energies, the decay of carotenoid triplets, which are very effi cient quenchers of chlorophyll singlet states, dominates the rise kine tics of the flash induced fluorescence yield in the mu s time domain.