Effects of Electrolyte and Non-Electrolyte Solutions on the Tropic Responses ofAvenaColeoptiles

Abstract

Solutions of mannitol and carbowax 1540 reduced the geotropic response of Avena sativa coleoptiles to at least the same extent as a potassium chloride solution of equal osmotic poten tial. Similar results were obtained with the phototropic response. The magnitude of these decreases increased almost linearly with the osmotic concentration of the solutions over the range 0-025-0-45 J cm 3. In contrast, the geotropic and phototropic responses were scarcely affected by exposing the coleoptiles to solutions of glycerol. The absence of an effect with glycerol is probably due to the penetration of the coleoptile cells by this solute. The similar or greater reduction in tropic curvature brought about by mannitol and carbowax 1540 solutions, as compared with a potassium chloride solution of equal osmotic potential, makes untenable a previous suggestion attributing the inhibitory effects of electrolyte solutions to a shunting of the electro-potential differences on the plant surface.