Characterization of New Strains of Photosynthesis Mutants of <italic>Chlamydomonas Reinhardtii</italic> IV Impaired Excitation Energy Transfer in Three Low Fluorescent Mutants

Abstract

Three new mutants of Chlamydomonas reinhardtii were characterized, which showed maximum Chl fluorescence yields close to the initial minimum level and clearly lower than the wild type maximum yield. Two of these mutants, mf 1 and mf 2, also showed anomalies characteristic of mutants lacking functional PS II: absence of PS II-related photochemical activity and of the variable component of fluorescence, deficiencies of high potential Cyt b-559, of the Chl-protein complexes CP III and CP IV and of five PS II-related proteins. The third mutant, mf 3, was able to perform photosynthesis and did not show any of the above deficiencies. Low-temperature fluorescence emission spectra indicated clearly that, whatever the oxido-reduction state of the plastoquinone pool, the emission of the main light-harvesting antenna at 682 nm was weaker and the emission of the PS I core antenna at 712–716 nm was more important in mf 1 and mf 2 than in a “classical” PS II-deficient mutant. In mf 3, unlike the wild type, the PS II-related emissions at 686 and 696 nm were relatively less important than that at 712–716 nm. Low-temperature fluorescence excitation spectra showed that, in the three mutants, the light captured by the main Chl a+b antenna, CP II, was the most efficient in inducing PS I fluorescence. These results indicate that, in the three mutants, the energy captured by the main light-harvesting antenna is always preferentially transferred towards PS I. They will be discussed in terms of membrane defects leading to an impaired regulation mechanism for the distribution of the excitation energy between the two photosystems.