ADAPTATIONS TO TEMPERATURE IN TWO CLOSELY RELATED STRAINS OF EUGLENA GRACILIS

¹ Laboratory of Nuclear Medicine and Radiation Biology, University of California. Los Angeles

1. Certain biochemical and physiological parameters in two closely related strains of Euglena gracilis (strain Z and var. bacillaris) have been examined after adaptation to various incubation temperatures.

2. The growth rate for the two strains differed at all temperatures, but was greatest in both at 29°.

3. Temperatures below optimal resulted in increased mass, protein, and RNA levels. In general E. gracilis var. bacillaris was larger in all these fractions at any given temperature.

4. Endogenous respiration proceeded at rates which were essentially unchanging over the temperature range 15°-29° C. Both strains exhibited the same rate.

5. Oxygen consumption in the presence of exogenous substrate (sodium acetate) increased in a linear fashion with the temperature of incubation, rates in strain Z being considerably greater than in var. bacillaris.

6. Mass, RNA, and protein content were found to be an exponential function of the growth rate, with a change in the sign of the slope at a growth rate of .05/hr. The rate of protein synthesis was a linear function of the rate of RNA synthesis in both strains.