Changes in hydrogen metabolism during greening of pigment mutant C-2A' from Scenedesmus obliquus [Chlorophyceae]

Capacities of H2-photoproduction and photoreduction were determined in the greening pigment mutant C-2A′ of Scenedesmus obliquus. In the dark grown culture the capacity for H2-photoproduction is low and for photoreduction not detectable. Both processes increase with chloroplast development in the light. Photoreduction increases in parallel to the photosynthetic capacity using H2 instead of water as electron donor. H2 reaches optimal values during the stage of highest quantum efficiency of photosynthetic oxygen evolution, but does not increase further. Hydrogenase of adapted cells is most active in dark grown cultures and declines during greening. This indicates that hydrogenase activity is not the limiting factor in the hydrogen metabolism studied in this investigation. Studies with cells in which the formation of the reaction centers were reversibly suppressed by chloramphenicol demonstrate that hydrogen metabolism depends on intact reaction centers and can not be mediated by light harvesting chlorophylls.