Picosecond time-resolved energy transfer in Porphyridium cruentum. Part I. In the intact alga.
The wavelength-resolved fluorescence emission kinetics of the accessory pigments and chlorophyll a in Porphyridium cruentum have been studied by pico-second laser spectroscopy. Direct excitation of the pigment B-phycoerythrin with a 530 nm, 6 ps pulse produced fluorescence emission from all of the pigments as a result of energy transfer between the pigments to the reaction centre of Photosystem II. The emission from B-phycoerythrin at 576 nm follows a nonexponential decay law with a mean fluorescence lifetime of 70 ps, whereas the fluorescence from R-phycocyanin (640 nm), allophycocyanin (660 nm) and chlorophyll a (685 nm) all appeared to follow an exponential decay law with lifetimes of 90 ps, 118 ps and 175 ps respectively. Upon closure of the Photosystem II reaction centres with 3-(3,4-dichlorophenyl)-1,1-dimethylurea and preillumination the chlorophyll a decay became non-exponential, having a long component with an apparent lifetime of 840 ps. The fluorescence from the latter three pigments all showed finite risetimes to the maximum emission intensity of 12 ps for R-phycocyanin, 24 ps for allophycocyanin and 50 ps for chlorophyll a. A kinetic analysis of these results indicates that energy transfer between the pigments is at least 99% efficient and is governed by an exp --At1/2 transfer function. The apparent exponential behaviour of the fluorescence decay functions of the latter three pigments is shown to be a direct result of the energy transfer kinetics, as are the observed risetimes in the fluorescence emissions.
D002734:Chlorophyll / Q000378:metabolism*; D004735:Energy Transfer; D005453:Fluorescence; D007834:Lasers; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis; D010798:Phycocyanin / Q000378:metabolism*; D010799:Phycoerythrin / Q000378:metabolism*; D010860:Pigments, Biological / Q000378:metabolism*; D000461:Rhodophyta / Q000378:metabolism* / Q000528:radiation effects; D013057:Spectrum Analysis
D010860:Pigments, Biological; D010798:Phycocyanin; D010799:Phycoerythrin; D002734:Chlorophyll; D010100:Oxygen