Watzke D, Machemer H Bräucker R, (1998): Graviresponses of iron-fed Paramecium under normal and hypergravity conditions.


Paramecium caudatum cells were fed with iron-particles to increase the density of the cytoplasm. The swimming speed and orientation of iron-fed and iron-free control cells were analyzed under terrestrial gravity and raised acceleration up to 6 g in a centrifuge. Iron-fed cells sedimented at increased rates (133 µm s-1 per g unit) as compared to controls (118 µm s-1 per g unit). Gravikinesis increased in iron-fed cells with rising acceleration at a rate of 67 µm  s-1 per g unit as compared to 46 µm s-1 per g unit in control cells. In particular, the gravikinesis of downward swimming iron-fed cells was strongly enhanced, thereby compensating for the sedimentation rate. This was not the case in upward swimming cells, where ingested iron depressed the gravikinetic response. The negative gravitaxis of Paramecium, as being represented by the cell orientation coefficient, was much pronounced in iron-fed cells at 1 g (roc = 0.36; controls: roc = 0.13). At 4 g, the orientation coefficient of iron-fed Paramecium rose to 0.80 (controls: 0.54). The effect of artificially raised cytoplasmic density on gravikinesis is explained at the basis of the mechanoreceptor organization of Paramecium. The effect on gravitaxis continues to be uncertain.