Effect of temperature in the regulation of DNA synthesis in synchronous cultures of Chlorella

The influence of temperature on DNA replication of Chlorella pyrenoidosa grown at 30 °C was studied in synchronous cultures. Final DNA content and cell counts/ml were 30 to 40% less than controls after a 4 h exposure to 15 °C, but reached normal levels after being kept temporarily at 10 °C. The rates of DNA synthesis at these two temperatures were, respectively, one-sixth and one-tenth of the rate at 30 °C, but during the 15 °C treatment the cells lost the ability to enter a further replication cycle more rapidly than at 10 °C. This loss of capacity to initiate further replication cycles was prevented by inhibiting protein synthesis with cycloheximide.