The Phototropic Responses of Avena Coleoptiles

Macleod, K., Firn, R. D. and Digby, J. 1986. The phototropicresponses of Avena coleoptiles.—J. exp. Bot. 37: 542–548. A number of studies of the elongation rate changes causing phototropismhave been made but the findings of different groups have notbeen entirely Consistent. Studies of oat coleoptile phototropismin response to first-positive and second-positive doses indicatethat no single pattern of elongation rate changes causes phototropismeven in a single species. The relative effect of phototropicstimulation on the elongation rate at the shaded or the illuminatedside of coleoptiles subject to unilateral illumination dependson physiological state of the cell-for instance its positionin the elongation zone or whether it has been given red lightrecently. Models of phototropism will have to account for sucha diversity of phototropic responses. The importance of makingfull elongation rate measurements has once again been demonstrated. Key words: Phototropism, first-positive, second-positive, phytochrome, coleoptile, elongation rate