CHAPTER THREE Water Flow in the Roots of Crop Species: The Influence of Root Structure, Aquaporin Activity, and Waterlogging H. Bramley, 1 , * D. W. Turner, † S. D. Tyerman,* and N. C. Turner ‡ Contents 1. Introduction 134 2. Water Movement Through the Plant 135 2.1. Driving forces 135 2.2. Hydraulic conductance 137 2.3. Hydraulic conductivity of roots (Lp r ) 138 3. Root Characteristics and Water Flow 140 3.1. Factors that influence root growth and water uptake 140 3.2. Root anatomy 141 4. Changes in Lp r 146 5. Plant Aquaporins (AQPS) 147 5.1. AQP structure 148 5.2. AQP selectivity 150 5.3. Control of water permeability 152 6. The Role of AQPs in Root Water Transport 167 6.1. Inhibition studies 167 6.2. Expression and transformation studies 169 6.3. The contribution of AQPs to radial water flow 170 7. Waterlogging 171 7.1. Effect on O 2 in the rhizosphere 171 7.2. Effect on root growth 172 7.3. Effect on water use 174 Advances in Agronomy, Volume 96 # 2007 Elsevier Inc. ISSN 0065-2113, DOI: 10.1016/S0065-2113(07)96002-2 All rights reserved. * Wine and Horticulture, Faculty of Agriculture, Food and Wine, The University of Adelaide (Waite Campus), Plant Research Centre, PMB 1, Glen Osmond, South Australia 5064, Australia { School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, Western Australia 6009, Australia { Centre for Legumes in Mediterranean Agriculture, The University of Western Australia, Crawley, Western Australia 6009, Australia 1 Present address: Department of Renewable Resources, 444 Earth Sciences Building, University of Alberta, Edmonton, Alberta T6G 2E3, Canada 133