Studies on the Control of the Rhythm of Photosynthetic Capacity in Synchronized Cultures of Euglena gracilis (Z) 1234

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Synchronous cell division in Euglena gracilis (strain Z) was obtained in 24-hour light cycles consisting of 10 hours of light and 14 hours of darkness; cell division was restricted to the dark period. Photosynthetic capacity was found to vary in a cyclic manner during the cell cycle, reaching a peak 2 hours before the onset of darkness. Light reactions were investigated during the cell cycle to determine what role they played in the control of the observed rhythmic changes in capacity. Light-saturation curves showed no major change in the light-limited region. No fluctuations were found in Hill reaction activity or photoreduction of methyl red during the cell cycle. These results imply that the reactions comprising photosystems I and II do not generate the capacity rhythm.

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