Water flow in the roots of crop species: The influence of root structure, aquaporin activity, and waterlogging

The hydraulic properties of plant roots depend on the morphology and anatomy of the root system, the length of the absorbing region and the influence of aquaporins (AQPs). These features change during development and in response to environmental stimuli, and alter the hydraulic conductivity of the root system (Lpr). AQPs are proteins that form water selective channels to facilitate water flow across membranes. A large proportion of AQP isoforms are predominantly expressed in roots and their localization indicates a putative role in the transport of water across the root. AQP activity can finely regulate the rate of water flow across the root by changes in abundance and opening/closing the water channels. Since water will flow by the pathway of least resistance, AQPs will only influence radial water flow if the hydraulic conductivity of the apoplast is relatively less than that of the cell-to-cell pathway. There is growing evidence that AQPs influence water flow through the roots of some, but not all, species. Waterlogging is a significant environmental constraint to crop growth, but its influence on Lpr is poorly understood. Depending on the tolerance of the species, waterlogging through oxygen deficiency reduces root growth and tends to reduce Lpr. Oxygen deficiency can directly or indirectly close AQPs or alter their abundance. Changes in AQP activity may be the key component which ultimately influences water transport through waterlogged roots. © 2007 Elsevier Inc. All rights reserved.