title: Day-night periodicity of exudation in detopped tobacco.
abstract: Exudate was collected periodically from the root systems of detopped tobacco plants. Volume, cations, and (42)K or (86)Rb transfer were measured. According to measurements of K by (42)K and by the flame photometer, when concentrations of KCl and KNO(3) were lower than 10(-2)m, the K in the exudate came mostly from a pool in the plant rather than from the external solution. With higher external KNO(3) solutions, within a few hours nearly all of the K in the exudate came directly from the external solutions. Studies with (86)Rb lead to the same conclusion. In contrast the maximum proportion of K in the exudate that came from KCl in the external solution was reached usually in many hours after detopping and amounted to from 50 to 75%. The higher the external concentration the faster it was reached. These data for KCl are indicative of the (42)K passing through a K pool in the root cells. K and Rb from high concentrations of KNO(3) and RbNO(3), however, may not pass through such a pool. The addition of 10(-2)m KNO(3) into the external solution during exudation essentially eliminated the effect of periodicity at least for a period of time and under the conditions of the experiments. Hydrochloric acid, mercuric chloride, anaerobiosis, and 2,4-dinitrophenol had the same effect and each resulted in a massive final exudation that usually persisted for 1 to 3 days before stopping. These results all lead to a hypothesis that periodicity is regulated at the tonoplast.
authors.affiliation: Department of Agricultural Sciences, University of California, Los Angeles, California 90024.
authors.forename: A
authors.initials: A
authors.lastname: Wallace
authors.forename: R T
authors.initials: RT
authors.lastname: Ashcroft
authors.forename: O R
authors.initials: OR
authors.lastname: Lunt