Evidence that the variable chlorophyll fluorescence in Chlamydomonas reinhardtii is not recombination luminescence

Room temperature single photon timing measurements on intact, Chlamydomonas reinhardtii cells at low excitation energies have been analysed using a four exponential kinetic model. Closing the PSII reaction centres produced two major variable lifetime and two minor constant lifetime components. The yield of each component mirrored the changes in lifetime. Such observations indicate the presence of well-connected PSII centres favoring excitation energy transfer. A Chlamydomonas mutant lacking PSII reaction centre proteins exhibited decay components equivalent to those seen at FM in the wild-type. A titration of in vivo fluorescence, in both the mutant and wild-type algae, using DNB, produced decay components similar to those seen on opening PSII reaction centres. Such observations indicate that the luminescence hypothesis for the origin of the long-lived lifetime component is not the case.