Studies on kinase-controiled state transitions in Photosystem II and $b_6 f$ mutants from $Chlamydomonas\ reinhardtii$ which lack quinone-binding proteins

Abstract : We have studied kinase-dependent state transitions in vivo using photosynthetic mutants from the green alga $Chlamydomonas\ reinhardtii$ lacking in quinone-binding proteins. The aim of our study was to identify proteins involved in the plastoquinone-dependent activation of the LHC-kinase. Whereas mutants totally devoid of the quinone-binding subunits D1 and D2 of Photosystem II showed unaltered state transitions, mutants lacking the $b_6 f$ complexes were incapable of state transitions. These mutants were blocked in State 1, which is indicative of either the absence of the LHC-kinase responsible for the regulation, or of the loss of a component responsible for the activation of this enzyme. These two hypotheses are discussed in light of (i) the patterns of phosphorylation of the thylakoid membrane proteins observed in the $b_6 f$ mutants and (ii) the characteristics of the kinase activities recovered from their thylakoids.