ADAPTATIONS TO TEMPERATURE IN TWO CLOSELY RELATED STRAINS OF EUGLENA GRACILIS 1 J. R. COOK 2 Laboratory of Nuclear Medicine and Radiation Biology, University of California. Los ^in/clcs A general pattern has emerged from the many studies of physiological adapta-tions to temperature in protozoans. Within the limits of tolerance, low tempera-tures result in reduced growth rate and increased cell size, the latter a result of increased amounts of practically all biochemical constituents. However, significant qualitative differences between species have also been reported. Thus, Johnson (1962) found that respiratory activity in the crypto-monad flagellate Chilomonas paramcciuin increased exponentially with tempera-ture, while Buetow (1963) showed that respiration in a colorless mutant of Englena gracilis var. bacillaris increased in a linear manner with temperature. The latter finding is of particular interest as an example of a continuously decreasing Q 10 with increasing temperatures. Qualitative differences of this sort must be an expression of genetic diversity among flagellates in a most fundamental aspect of protozoan physiology. Because of this, it seemed desirable to repeat Buetow's work with a wild-type Euglena. This report describes some physiological properties of two strains of Euglena gracilis, separated only by minor taxonomic differences, as a function of incubation temperature. These studies show marked quantitative but no qualitative differ-ences in temperature adaptation between the two strains. Buetow's report of a linear increase in respiratory activity with elevated temperatures is confirmed when exogenous acetate is available, but a markedly different pattern was observed in endogenous respiration. Other parameters mass, protein, and RNA respond in the expected manner. METHODS Original stocks of the cells used, Euglena gracilis strain Z and Euglena gracilis var. bacillaris, were obtained from Dr. J. A. Gross and have been maintained through serial culture by the author. Growth rates of these stocks, measured under the same culture conditions, have remained constant over a period of years. For these studies, however, a single colony of each strain was picked off agar, inoculated into liquid media, and the resulting populations used. These two clonal popula-tions, derived from single cells, did not differ in growth rate from the parent populations. The salt medium of Cramer and Myers (1952), with sodium acetate (25 mM) as sole carbon and energy source, was used exclusively. Axenic cultures were 1 Supported by Contract AT (04-1) GEN-12 between the Atomic Energy Commission and the University of California. 2 Present address : Department of Zoology, University of Maine, Orono, Maine 04473. 83
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