title: Action spectra for photosynthetic adaptation in Scenedesmus obliquus : I. Chlorophyll biosynthesis under autotrophic conditions.
abstract: Photosynthetic adaptation of the unicellular green alga Scenedemus obliquus to different light conditions was investigated with respect to chlorophyll synthesis. Cultures were grown under white light (20 W · m(-2)) from fluorescent lamps and were then transferred and subjected to the actual adaptation regime which consisted of a 24-h irradiation by different fluence rates and wavelengths. Fluence rate-response curves for chlorophyll synthesis were measured between 4 · 10(-2) and 1 · 10(2) W · m(-2). In white light from incandescent lamps, in blue and red light the fluence rate-response curves for chlorophyll (Chl) a and also for Chl b were bell-shaped. In red light the threshold was about the same as under blue light. The maximal amounts of Chl a and b were about twofold increased under blue light relative to the values obtained with red light. Action spectra for the stimulation of chlorophyll synthesis (Chl a + Chl b) as well as those for the separate chlorophylls showed two maxima near 450 and 500 nm. However, the action spectrum for Chl b synthesis demonstrated a considerably higher value in the 450-nm peak. Experiments with the photosynthesis inhibitor 3-(3,4-dichlorphenyl)-1,1-dimethylurea (DCMU) indicated that photosynthetic energy supply supported the photostimulation of chlorophyll synthesis. The action spectra indicate the cooperation of two photoreceptors. The 460-nm peak is attributed to the "typical" blue-light receptor, being more active in Chl b formation. The peak at 500 nm may represent carotenoproteins acting as an accessory pigment system.
authors.affiliation: Fachbereich Biologie/Botanik, Philipps-Universität Marburg, Lahnberge, W-3550, Marburg, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Thielmann
authors.forename: P
authors.initials: P
authors.lastname: Galland
authors.forename: H
authors.initials: H
authors.lastname: Senger