MUTANTS OF CHLAMYDOMONAS-REINHARDTII AFFECTED IN PHOSPHATIDYLGLYCEROLMETABOLISM AND THYLAKOID BIOGENESIS

Four mutants of Chlamydomonas reinhardtii have been isolated. The mfi and mf2 strains are not photosynthetically active because they lack PS II activity; they are also devoid of Delta(3)-trans-hexadecenoic acid- containing phosphatidylglycerol, and are almost unable to form trimeri c LHC2 or develop thylakoid appressions. Seventy-seven K fluorescence emission spectra have shown that mf1 and mf2 mutants are unable to per form significant state transition and are blocked in a permanent state II. The photosynthetic Pmf1 and Pmf2 strains were respectively select ed from mf1 and mf2 mutants grown on a minimal medium. Compared to wil d type cells, the Pmf1 mutant had about 5 % of Delta(3)-trans-hexadece noic acid-containing phosphatidylglycerol, a weak oxygen evolution act ivity, the capacity to form low amounts of trimeric LHC2 and a signifi cant level of membrane stacking. A similar partial restoration of the wild type phenotype was observed in the Pmf2 mutant, but to a larger e xtent: the recovery of about 50 % of Delta(3)-trans-hexadecenoic acid- containing phosphatidylglycerol is correlated with the recovery of abo ut 50 % of PSII activity, large amounts of trimeric LHC2 and stacking of photosynthetic membranes. These results demonstrate a clear corresp ondence between the level of Delta(3)-trans-hexadecenoic acid-containi ng phosphatidylglycerol, the formation of the trimeric LHC2 and the de velopment of grana stacks. The direct involvement of this lipid in the se characteristics was demonstrated by the restoration of trimeric LHC 2, appressed thylakoids and state I/state II transitions in mf1 and mf 2. mutants after in vivo selective targeting of Delta 3-trans-hexadece noic acid-containing phosphatidylglycerol in their photosynthetic memb ranes. (C) Elsevier, Paris.