Circadian rhythm of gravitaxis in Euglena gracilis.
Euglena gracilis, a unicellular, photosynthetic flagellate is a model system for environmentally controlled behavioral reactions. One pronounced reaction is the orientation with respect to gravity. In synchronized cultures with no cell growth a distinct circadian rhythm of negative gravitactic orientation could be observed. The main maximum of sensitivity was detected 5 h after the beginning of the subjective day, the main minimum 5 h before the beginning of the subjective day. Transferring synchronized cultures to continuous light resulted in an almost instantaneous loss of rhythmicity. In contrast, after transfer to permanent darkness cells exhibited a circadian rhythm with a progressive shortening of the period for more than 5 days. These findings are in contrast to the circadian rhythm of phototaxis in Euglena, where a free-running period of 24 h was observed. Parallel measurements of negative gravitactic orientation, velocity, cell shape as well as cAMP concentration in synchronized cultures revealed a circadian rhythm of all reactions. The results are discussed with regard to the possible role of cell shape and cAMP in gravitactic orientation.
Lebert
M
M
Friedrich-Alexander-Universitat, Institut fur Botanik und Pharmazeutische Biologie, Erlangen.
Porst
M
M
Hader
D P
DP
D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D000242:Cyclic AMP / Q000378:metabolism* / Q000502:physiology; D005056:Euglena gracilis / Q000502:physiology*; D018466:Gravity Sensing; D008027:Light; D009043:Motor Activity; D009949:Orientation; D010775:Photic Stimulation
D000242:Cyclic AMP