Studies on the induction of chlorophyll fluorescence in barley protoplasts. II. Resolution of fluorescence quenching by redox state and the transthylakoid pH gradient

Abstract

During the chlorophyll fluorescence oscillation described in barley protoplasts (Quick & Horton, Proc. R. Soc. Lond. B 220, 361-370, 1984) the components which contribute to quenching have been quantified. Quenching due to oxidized Q (q_Q) was measured either by DCMU addition or by light doubling and indicated an oscillation in the redox state of Q which was antiparallel to the rate of oxygen evolution but was approximately 15 s out of phase at a variety of light intensities and temperatures. An oscillation in the extent of energy-dependent quenching, q_e, was observed in strong but not weak light. These results are discussed in terms of the mechanism of the changes in energy and redox states that can contribute additively but in differing proportions to the fluorescence oscillation.