Gravitaxis screened for physical mechanism using g-modulated cellular orientational behaviour.

Advanced methods of recording cellular orientation with respect to the gravity vector are yielding increasingly wellfounded data on gravitaxis. The present study introduces a quantitative method which allows us 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 as derived from circular statistics. Orientation coefficients calculated from experimental data at various g-values are tested for fit with a sigmoidal orientation coefficient-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 orientation coefficient-g-relationship gives the minimal acceleration to generate cellular orientation. Those data which clearly diverge from the orientation coefficient-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 orientation coefficient-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.