A Quantitative Study of Cellular Rheotropism.

Sparsely sowed, hence independent Botrytis spores, which are fixed to the wall of a laminar flow chamber, tend to germinate downstream. For a velocity, v(infinity), one cell radius from the wall, of 0.1 to 1000 mu/second, this tendency, expressed as a percentage of perfect orientation, approximates 9 . log (10 v(infinity)). Indirect proof is given that this rheotropic response is mediated by the convection across each cell of a diffusible stimulator emitted by it. Analysis of the response indicates that this stimulator has a diffusion constant of the order of 10(-7) cm(2)/second and thus is macromolecular, and a half-life of the order of 10 seconds and thus a radius of action in a stagnant medium of about one cell diameter. The rate of germination falls so slowly with increasing flow rate as to indicate a much lower sensitivity of the rate than of the localization of growth to this stimulator's concentration.