[Rhythmic behavior of a colorless mutant of Euglena gracilis]

A colorless mutant of Euglena gracilis shows a cireadian rhythmic mobility in darkness just as mixotrophic and autotrophic green forms do.Therefore the obligatory heterotrophic form is very suitable for testing to what extent the rhythmic behavior of the mixotrophic cells, in contrast to that of the autotrophic cells, is independent of photosynthesis.Like the green cells, the colorless cells are synchronized by a single transient from light to dark. About 12 hours after the beginning of the darkness the rhythmic mobility of the colorless cells attains the first maximum, whereas the green forms both show their first maximum 18 hours after the end of the light period, which is much more advantageous for a photosynthesizing organism.The free running period seems to be dependent on the temperature during anaerobic glycolysis and independent of temperature during respiration, just as it has been recently found out in the case of green forms. The type of energy supply changes with the age of the cultures.Respiration has no significance as energy source for the rhythm which continues under pure glycolytic conditions.A sudden increase of the constant temperature does not shift the phase. The same is true in the case of mixotrophic cells but not in the case of autotrophic cells. However, the rhythm is often first suppressed for several days.A lowering of the temperature is followed by two or three transients with about half the frequency, but it does not influence the phase as far as it can be extrapolated. The same has been shown to be true in the case of mixotrophic cells.The rhythmic behavior of the heterotrophic cells is very similar to that of the mixotrophic ones. However, the heterotrophic cells are very sensitive to changes in temperature, which are more compensated for in the mixotrophic cells, apparently by photosynthesis.