EXCITATION ENERGY TRANSFER IN THE LIGHT HARVESTING ANTENNA SYSTEM OF THE RED ALGA<i>Porphyridium cruentum</i>AND THE BLUE‐GREEN ALGA<i>Anacystis nidulans</i>: ANALYSIS OF TIME‐RESOLVED FLUORESCENCE SPECTRA

Abstract

Abstract— Time‐resolved fluorescence spectra of intact cells of red and blue‐green algae Porphyridium cruentum and Anacystis nidulans were measured by means of a ps laser and a time‐correlated photon counting system. Fluorescence spectra were observed successively from various pigments in the light harvesting system in the order of phycoerythrin (PE), phycocyanin (PC), allophycocyanin (APC) and chlorophyll a (Chl a ). The spectrum changes with time in the range of0–400 ps in P. cruentum and of0–1000 ps in A. nidulans . The time‐resolved spectra were analyzed into components to obtain the rise and decay curve of each fluorescence component. Overall time behaviors of the sequential fluorescence emissions from various pigments can be interpreted with a decay kinetics ofexp(–2 kt ½ ). The rate constants of the energy transfer show that the energy transfer takes place much faster in the red alga P. cruentum than in the blue‐green alga A. nidulans , particularly in the step PCAPC. Results also indicated that a special form of APC, far‐emitting APC, exists in the pigment system of A. nidulans , but it does not mediate a main energy transfer from phycobilisome to Chl a.