FLUORESCENCE INDUCTION IN THE RED ALGA PORPHYRIDIUM CRUENTUM

Abstract— The intensity dependence and the spectral changes during the fast (sec) and the slow (min) transient of chlorophyll (Chl) a fluorescence yield, measured at 685 nm, have been analyzed in the red alga Porphyridium cruentum . Both the fast and the slow fluorescence yield changes are affected differently by the inhibitors of electron transport ( e.g ., DCMU) and by the uncouplers of phosphorylation (atebrin and FCCP). Fixation of Porphyridium cells with glutaraldehyde abolishes most of the fluorescence yield changes except for the so-called very fast ( OI ) phase. The same fixed cells, however, reduce DCPIP (a Hill oxidant) but do not evolve O₂ when CO₂ is used as electron acceptor. We interpret these and other results by the hypothesis that fluorescence transients in intact cells are linked to both electron transport and the energy dependent structural changes in the thylakoid membrane.