Watzke D, Bräucker R (1996): Gravity response of Paramecium caudatum modified by iron feeding

Paramecium shows a well known gravitactic behaviour. We assume that gravity induced active modulation of swimming velocity (gravikinesis) is mediated by the mechanical load of the cytoplasm acting on mechanoreceptor channels of the plasma membrane. Following iron-feeding the density of the cytoplasm was increased by at least 13%. In order to determine gravikinesis, upward and downward swimming rates, cell orientations and sedimentation rates were analyzed using computer-aided video analysis. Ingestion of iron-particles was completed after 20 minutes. Iron uptake increased the precision of graviorientation. During the first 15 minutes of recording (55 min. after beginning of iron-feeding) the swimming rates of iron-fed cells were larger than those of control samples. In both experimental groups the swimming rates decreased with time; swimming rates coincided 60 minutes after the beginning of iron-feeding. In the control cells, the gravikinesis neutralized the effect of sedimentation. In the iron-fed cells sedimentation was more than compensated by gravikinesis. The iron-induced potentiation of gravikinesis decreased with time. Evaluations show that gravikinesis in both iron-fed cells and control cells is a function of the orientation angle of the cell.