Low-temperature (4-77°k) Spectroscopy of Chlorella; Temperature Dependence of Energy Transfer Efficiency

From the absorption spectra and the excitation spectra of chlorophyll a fluorescence measured (4-77 °K) at different wavelengths (685-760 nm) and their comparison with the emission spectra published elsewhere 23, we confirm that both the Pigment Systems (I and II) contain chlorophyll b, chlorophyll a 670 and chlorophyll a 678. But System II is relatively enriched in chlorophyll b and System I in chlorophyll a 685715 . Moreover, our data suggest the following correspondence between absorption and fluorescence bands: chlorophyll a 678 is responsible for F687, "Trap I I" for F698 and chlorophyll a 685-715 for F725. The efflciencies of energy transfer from chlorophyll b to chlorophyll a and from chlorophyll a 67o to chlorophyll a 678 that approach IOO % even at 4°K were found to be independent of temperature (4-295 °K). However, transfer efficiencies from chlorophyll a to the suggested trap of System II may be temperature dependent.