Photosynthetic Activity during the Life Cycle of Synchronous Skeletonema Cells

Abstract

AbstractA culture of Skeletonema costatum grown at a light intensity of 3 klux and at 20°C was synchronized in diurnally intermittent illumination of 12 hour light and 12 hour dark. The culture was hardly fully synchronous as the cell division period lasted about 9 hours. The cell division started in the middle of the light period. The concentration of the pigments: chlorophyll a, chlorophyll 6 and fucoxanthin and the rate of light‐saturated photosynthesis were followed every hour during the 24 hour period. Both the concentration of pigments and the photosynthetic activity showed a rhythmical variation. The concentration per cell of all three pigments examined increased during the development of the cells and decreased automatically during the period of cell division. An increase in the pigment concentration was found only in the light period. The rate of light‐saturated photosynthesis calculated per unit of cell number increased during the cell development and decreased during the division period. The increase in the photosynthetic activity at light‐saturation started about 4 hours after the end of cell division, which was 4 hours before the light was turned on while the increase in the concentration of chlorophyll a first started 1–2 hours after this moment.The variation in photosynthetic activity was compared with that found by other workers. The results found with Chlorella ellipsoidea by Japanese scientists (Nihci et al.) was explained as an inhibition phenomenon because the cells were not adapted to the experimental conditions.