A Kinetic Model for Phototropic Responses of Oat Coleoptiles

Publisher Website
Google Scholar
Abstract
A kinetic model is constructed to account qualitatively and quantitatively for the phototropic dosage-response curves of oat coleoptiles (Avena sativa) described previously. Three separate systems are defined corresponding roughly to 1st positive, 1st negative and 2nd positive curvatures. System I may be described by a photochemical activation of pigment followed by a light dependent inactivation, the active species mediating lateral translocation of auxin. System II is similar to system I but mediates auxin translocation in the opposite direction and is responsible for negative curvature. Both systems I and II are dependent only on the product of intensity (I) x exposure time (t). In system III, a light dependent equilibrium is established between a pigment and an excited form of this pigment, the latter being converted via a dark reaction to a phototropically active substance. Phototropic response increases linearly as a function of t in system III and is independent of intensity. The kinetin model for system III also accounts for the fact that flashing light will produce larger curvatures than the same dosage administered continuously.