The biological clock of Chlamydomonas reinhardii in space.

The overt circadian rhythm in a wildtype (wt+) and a short period (s-) strain of Chlamydomonas reinhardii has been studied in space using the photoaccumulation behavior as the recorded parameter. The period of the wt+ was 29.6 h, of the s- 21.4 h and did not deviate significantly from ground controls performed exactly at the same time. The phase was delayed in space by 4.2 h in the wt+, but was not altered in the s-. In both strains the amplitudes were significantly higher in space than in the ground controls. During the recording period of 6.5 days the cell density increased in both strains. The survival rate, i.e. the ability to form colonies on agar petri dishes, was higher in space than on ground. The period was in both strains by 1.1 h longer in Florida (Kennedy Space Center) in both the flight and the control samples than in Europe. The significance of these results is discussed with respect to the endogenous nature of the biological clock and the role of the microgravity environment.