Picosecond Time-Resoved Fluorescence Spectroscopy of Excitation Energy Transfer-Photoexcitation Transport in Light-harvesting Antenna System in Algae-

Abstract

Time-resolved fluorescence spectra of intact cells of red and blue-green algea, Porphyridium cruentum and Anacystics nidulans, were measured by means of a picosecond 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 (Chla). The spectrum changes with time in the range of 0-400 ps in P. cruentum and of 0-1000 ps in A. nidulans. The time-resolved spectra were analyzed into components to obtain the rise and decay curve of each fluorescence component. The time behaviors of sequential fluorescence emissions from the pigment system can be interpreted with the decay kinetics of an exp (-2kt^1/2) type. 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 PC→APC step. The results also indicate that a far-emitting APC (APC B etc) does not mediate a main energy transfer from phycobilisome to Chl a.