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Not in Pubmed!; International audience; Mutant strains of the cyanobacterium Synechocystis 6803 were constructed in which either the apcABC operon, encoding core subunits allophycocyanin alpha and beta and a small linker L 8, or the apcE gene encoding the phycobilisome core-membrane linker was deleted. Phycobilisome assembly and energy transfer were studied in these mutants using both SDS gel analysis of phycobiliprotein complexes and low temperature fluorescence spectroscopy. Both mutants assembled phycocyanin rods but neither assembled a core complex. Although the mutants have no functional phycobilisomes, they grow photoautotrophically. No energy transfer between the remaining soluble phycobiliproteins and the photosystems was observed.

We have studied the electron transfer properties of Photosystem II using several techniques (fluorescence, oxygen emission and thermoluminescence measurements) in a series of herbicide-resistant mutants from widely different organisms. Five mutants of Synechocystis 6714, of which we have determined the D1 sequence, one mutant of Synechococcus 7942, one mutant of Chlamydomonas reinhardtii , a triazine-resistant biotype of Chenopodium album and their herbicide-susceptible controls were analyzed. Two mutants have an almost unimpaired Photosystem II electron transfer. For five mutants of the different organisms, the initial phase of the electron transfer Q − A to Q B is unaltered but the electron transfer equilibrium between these two acceptors is displaced. In the Chlamydomonas -resistant mutant, the electron transfer from Q − A to Q B is slowed down.