OBSERVATIONS ON CELL DEVELOPMENT INCHLAMYDOMONAS SEGNIS(CHLOROPHYCEAE) AT LOW AND HIGH CARBON DIOXIDE TENSION1

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Abstract
Some cell cycle events were compared inChlamydomonas segnisEttl during its development in synchronous cultures (12:12 LD) supplied with air and air enriched with 5% CO2. In cultures bubbled with air, growth resulted in production of 2 relatively small zoospores. In cultures provided with 5% CO2, 4 large zoospores were formed but not released in darkness unless the cultures were bubbled with CO2‐free air and/or exposed to light. Respiration in zoospores was inhibited by high CO2tension. In cultures maintained under continuous illumination for one cell cycle, provision of 5% CO2led to enhanced growth, a relatively long S‐phase and a 4 h delay of the second cell division. In such cultures, the DNA content of parental cells (12 h L) was insufficient to support two cell divisions. The RNA/DNA ratio of the resulting zoospores was 10 compared to 4 in air cultures. These results provided evidence that the delay of the second cell division was a consequence of the delay in DNA production.