Machemer H, Bräucker R (1996) Gravitaxis screened for physical mechanism using g-modulated orientational cellular behaviour.


Advanced methods of recording cellular orientation with respect to the gravity vector are yielding increasingly well-founded data on gravitaxis. The present study introduces a quantitative method which allows to predict the precision of orientational behaviour as a function of acceleration assuming static buoyancy as a hypothetical physical principle of gravitaxis. The precision of orientation is expressed by the orientation coefficient (ro) as derived from circular statistics. Orientation coefficients calculated from experimental data at various g-values are tested for fit with a sigmoidal ro-g transfer function including a proportionality factor k. Residual orientation values in the low-hypogravity range obey a reciprocal function between k and g. Intersection of this residual-g function with the ro-g relationship gives the minimal acceleration to generate cellular orientation. Those data which clearly diverge from the ro-g curve bear some probability that the observed gravitaxis was guided in part by a physiological mechanism of gravireception and active graviorientation. Data which fit the ro-g curve qualify as being in agreement with a mechanical basis of cellular gravitaxis. Examples from the literature are presented and discussed in the light of our scheme of gravitaxis screening.