Photosynthetic capacity and quantum requirement of three secondary mutants of Scenedesmus obliquus with deletions in carotenoid biosynthesis

Photosynthetic capacity and quantum requirement of photosynthesis were evaluated in three secondary mutants of Scenedesmus obliquus possessing specific blocks in carotenoid biosynthesis. These were derived from the mutant, C-2 A', a strain which develops chlorophyll only in the tight. All strains were capable of a normal and rapid production of chlorophyll and the development of a functional photosynthetic apparatus when exposed to light. LHC-II levels in the mutants lacking the beta,epsilon-carotenoids (strains C-2 A'-34,1 and C-2 A'-67, 3b) were considerably reduced in fully greened cells but normal in the beta,beta-epoxycarotenoid deficient-only strain (C-2A'-67,1) (Bishop, 1996). The maximum photosynthetic capacity and the quantum efficiency (at lambda = 682 nm) of photosynthesis of cells of C-2 A'-34,1 and C-2 A'-67,1 showed no significant changes when compared to the original parent strain, C-2 A'. However, the quantum requirement of the strain lacking both types of carotenoids, C-2 A'-67,3b, was slightly increased. It is of particular interest that both strains lacking the beta,epsilon-carotenoids also show a preferential loss of the oligomeric form of the LHC and its associated chlorophylls. The potential requirement of the different carotenoids in maintenance of photosynthetic efficiency in Scenedesmus is discussed.