Observations on Cell Development Inchlamydomonas Segnis(chlorophyceae) at Low and High Carbon Dioxide Tension¹

Some cell cycle events were compared in Chlamydomonas segnis Ettl during its development in synchronous cultures (12:12 LD) supplied with air and air enriched with 5% CO 2 . In cultures bubbled with air, growth resulted in production of 2 relatively small zoospores. In cultures provided with 5% CO 2 , 4 large zoospores were formed but not released in darkness unless the cultures were bubbled with CO 2 ‐free air and/or exposed to light. Respiration in zoospores was inhibited by high CO 2 tension. In cultures maintained under continuous illumination for one cell cycle, provision of 5% CO 2 led 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.