Aquaporins and Root Water Uptake

Abstract

Water is one of the most critical resources limiting plant growth and crop productivity, and root water uptake is an important aspect of plant physiology governing plant water use and stress tolerance. Pathways of root water uptake are complex and are affected by root structure and physiological responses of the tissue. Water travels from the soil to the root xylem through the apoplast (i.e., cell wall space) and/or cell-to-cell, but hydraulic barriers in the apoplast (e.g., suberized structures in the endodermis) can force water to traverse cell membranes at some points along this path. Anytime water crosses a cell membrane, its transport can be affected by the activity of membrane-intrinsic water channel proteins (aquaporins). We review how aquaporins can play an important role in affecting root water transport properties (hydraulic conductivity, Lp), and thus alter water uptake, plant water status, nutrient acquisition, growth, and transpiration. Plants have the capacity to regulate aquaporin activity through a variety of mechanisms (e.g., pH, phosphorylation, internalization, oxidative gating), which may provide a rapid and reversible means of regulating root Lp. Changes in root Lp via the modulation of aquaporin activity is thought to contribute to root responses to a broad range of stresses including drought, salt, nutrient deficiency, and cold. Given their role in contributing to stress tolerance, aquaporins may serve as future targets for improving crop performance in stressful environments.