Changes in light energy distribution upon state transitions: An in vivo photoacoustic study of the wild type and photosynthesis mutants from Chlamydomonas reinhardtii

We investigated, by a photoacoustic method, the changes in light energy distribution to the reaction centres upon state transitions in vivo in Chlamydomonas reinhardtii. We present spectra of the quantum yield of charge separation in the wild type and in several photosynthesis mutants lacking either cytochrome b(6)f complexes, the PS II cores or the PS I cores. Our results show unambiguously that in the wild-type LHCII becomes connected to PS I in state 2, in a cyt b(6)f-controlled process, We show that mutants lacking the PS II cores, but not those lacking PS I cores, display a behaviour very similar to that of the wild type upon state transition. Lateral displacement of LHCII, but not of minor antenna complexes (CP26), from the stacked to the unstacked membrane domains results in transfer to PS I of about 80% of the excitation energy absorbed by LHCII. Consequently, in state 2, more than 90% of the chlorophylls transfer energy to PS I in mutants lacking PS II cores. In contrast, a significant proportion of the PS I peripheral antenna is connected with PS II, in state 1 as well as in state 2, in mutants lacking PS I cores. Moreover, in these mutants, phospho-LHCII remains part of PS II antenna in state 2. We attribute these features to the super-stacked organization of the thylakoid membranes in the PS I deficient mutants.