GRAVIRESPONSES OF IRON-FED PARAMECIUM UNDER HYPERGRAVITY

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 gravit y and raised acceleration up to 6 g in a centrifuge. Iron-fed cells se dimented at increased rates (133 mu m.s(-1) per g unit) as compared to controls (118 mu m.s(-1) per g unit), Gravikinesis increased in iron- fed cells with rising acceleration at a rate of 67 mu m.s(-1) per g un it as compared to 46 mu m.s(-1) per g unit in control cells. In partic ular, the gravikinesis of downward swimming iron-fed cells mas strongl y enhanced, thereby compensating for the sedimentation rate, This was not the case in upward swimming cells, where ingested iran depressed t he gravikinetic response, The negative gravitaxis of Paramecium, as be ing represented by the cell orientation coefficient, was much pronounc ed in iron-fed cells at 1 g (r(oC) = 0.36; controls: r(oC) = 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 densit y on gravikinesis is explained at the basis of the mechanoreceptor org anization of Paramecium. The effect on gravitaxis continues to be unce rtain.