Coordination of Root Hydraulic Conductivity and Transpiration in Honey Locust (Gleditsia triacanthos L. ): A Proposed Role for Aquaporins

Abstract

Plants exhibit rhythmic behavior in response to daily cycles of light and darkness. Such rhythms have been reported in leaf and petal movements, stomatal behavior, root resistance to water movement and solute transport in roots. It has been reported that when plants are transferred from recurring daily light and dark cycles to continuous darkness or continuous light, many such rhythms continue to be expressed for one or more periods. In constant light or darkness, rhythms generally have been observed to depart from 24-h periodicity (Sweeney, 1987). Several such rhythmic behaviors (e.g., stomatal movement) have been thoroughly characterized, and their physiological significance has been extensively documented. Many others have not been studied in sufficient detail, and our understanding of their physiological function is rather limited. For example, water homeostasis in plants is achieved by coordinated control of root water uptake from the soil and by transpiration through the stomata. Therefore, fine control of stomatal aperture and root hydraulic conductivity is essential for the maintenance of a favorable plant water status. Nevertheless, the rhythmic behavior of stomatal aperture and root resistance to water movement have never been functionally associated or explicitly studied as a potentially coordinated system that may regulate water homeostasis in plants.