Changes in the pigment patterns and the photosynthetic activity during a light-induced cell cycle of the green alga Scenedesmus armatus

The photosynthetic oxygen evolution as well as the chlorophyll and carotenoid patterns were studied during the light phase (14 h) of the Scenedesmus armatus cell cycle. The alga was synchronised by the light/dark regime (14/10 h). In this publication, the term “cell cycle” refers to this period of light only. The oxygen evolution measured by a Clark-type electrode and expressed per cell, gradually increased from the beginning of the cell cycle, reaching its maximum at 12 h and then slowly declined towards the end of the cell cycle. This pattern reflects the final reproductive events of the cell cycle consisting of the third mitotic division, chloroplast and protoplast fission, followed by the formation of the autospores. When the same amount of oxygen was expressed per chlorophyll a content, we observed a rapid increase just after the onset of light, which reached a maximum at the third hour, after which, this slowly declined until the end of the cell cycle. A similar pattern for the relative quantum yield of oxygen evolution was obtained when a photobaric component of a photoacoustic signal was analysed by the photoacoustic spectroscopy method. The most abundant carotenoid was lutein. Much smaller amounts of α-carotene, β-carotene, loroxanthin, violoxanthin and neoxanthin were noted; traces of zeaxanthin and antheraxanthin were also identified. The photosynthetic efficiency and the ratio of lutein/α-carotene followed the same patterns during the cell cycle and similar relationships were also observed in the ratio changes of violoxanthin/β-carotene and violoxanthin/neoxanthin. The most photosynthetic-efficient cells contained the highest level of lutein, and had a much lower violoxanthin content. The content of neoxanthin and β-carotene found was lower, with both pigments still being present in similar amounts. These results suggest that the molecular organisation of LHC IIb mainly determined the photosynthetic efficiency of algae during its light-induced cell cycle.