**Machemer
H, Bräucker R (1996) Gravitaxis screened for physical mechanism
using g-modulated orientational cellular behaviour.**
**Abstract.**
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
(r_{o}) as derived
from circular statistics. Orientation coefficients calculated from
experimental data at various g-values are tested for fit with a
sigmoidal r_{o}-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 r_{o}-g relationship gives the minimal acceleration to generate
cellular orientation. Those data which clearly diverge from the
r_{o}-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 r_{o}-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. |