INFLUENCE OF ELECTROLYTES ON GROWTH, PHOTOTROPISM, NUTATION AND SURFACE-POTENTIAL IN ETIOLATED CUCUMBER SEEDLINGS

A variety of electrolytes (10-30 mol m-3) increased the relative growt h rate of etiolated cucumber (Cucumis sativus L. cv. Burpee's Pickler) hypocotyls by 20-50% relative to water-only controls. The nonelectrol yte mannitol inhibited growth by 10%. All salts tested were effective, regardless of chemical composition or valence. Measurements of cell-s ap osmolality ruled out an osmotic mechanism for the growth stimulatio n by electrolytes. This, and the nonspecificity of the response, indic ate that an electrical property of the solutions was responsible for t heir growth-stimulating activity. Measurements of surface electrical p otential supported this reasoning. Treatment with electrolytes also en hanced nutation and altered the pattern of phototropic curvature devel opment. A novel analytical method for quantitating these effects on gr owth was developed. The evidence indicates that electrolytes influence an electrophysiological parameter that is involved in the control of cell expansion and the coordination of growth underlying tropisms and nutations.