Secondary carotenoid accumulation in Scenedesmus komarekii (Chlorophyceae,Chlorophyta)

As Scenedesmus komarekii Hegewald was cultured under high light intensity a nd nitrogen limitation, the color of cells progressed from green to brown, and finally through orange to brick red. The secondary carotenoids astaxant hin and canthaxanthin, as well as apolar carotenoids, were detected in the brown and orange cells. These carotenoids were contained in lipoidal globul es that were first formed at the periphery of the cell and progressively pr opagated toward its inside, eventually filling most of it. The chloroplast was single and parietal in the green cells. As the cells turned brown, the chloroplast divided into several small lobes and was pushed toward the inte rior by the accumulating lipoidal globules, Sometimes the outer layer of th e wall of the brown cell developed one or two diametrically opposed swellin gs, Once the cells became orange or red, neither lipoidal globules nor any major organelles were distinguishable. The cell wall in the orange cells be came thick because of the formation of electron-dense granules between its outer and inner layers. The mode of the secondary carotenoid accumulation i n S. komarekii differs from that of Haematococcus, an alga well known for i ts ability to accumulate secondary carotenoids, but resembles that of "Chlo rella" zofingiensis (= Mychonastes zofingiensis (Donz) Kalina et Puncocharo va).