EXCITATION ENERGY TRANSFER IN THE CRYPTOPHYTES. FLUORESCENCE EXCITATION SPECTRA AND PICOSECOND TIME‐RESOLVED EMISSION SPECTRA OF INTACT ALGAE AT 77 K

Abstract

AbstractExcitation spectra of chlorophyll‐a (Chl‐a) fluorescence in intact cells of Cryptomonas ovata, Chroomonas pauciplastida and Chroomonas salina were determined at 77 K. For all species the excitation spectra for emission from Chl‐a associated with photosystem II (PSII) showed increased contributions by a carotenoid (493 nm) and phycobiliproteins, and decreased contributions by carotenoid (417 nm, 505 nm) and Chl‐a (445 nm) as compared to excitation spectra for emission from Chl‐a associated with photosystem I (PSI). Excitation spectra of C. salina and C. ovata showed an increased contribution by Chl‐c2 to PSII Chl‐a fluorescence emission. In all three species the absorbance band positions of Chl‐a, as determined from the excitation spectra, were similar to those previously described in green plants. green algae and phycobilisome‐containing organisms. Time‐resolved 77 K fluorescence emission spectra of C. ovata and C. salina showed successive emission from both phycoerythrin and Chl‐c2, PSII Chl‐a, and PSI Chl‐a. C. pauciplastida showed successive emission from phycocyanin, PSII Chl‐a, and PSI Chl‐a. Spectral red‐shifts with time were observed for the phycobiliprotein peaks in all three species. The fluorescence decay of phycoerythrin in C. ovata and C. salina was faster than that of phycocyanin in C. pauciplastida. The results are discussed in relation to the organization of the antenna pigments of PSII and PSI in the cryptophyte algae.