7 - Water flow in roots: Structural and regulatory features

Abstract

This chapter examines the structural components of the radial pathway for water flow in roots and discusses possible regulators of water movement through both radial and axial pathways, specifically, aquaporins and embolism, respectively, and how these change during development and water stress. It considers how water stress might also affect the proportional limitations imposed by the two pathways on overall water transport by roots. In herbaceous plants in moist soil, rates of axial flow are usually high enough that the primary limitation for water transport occurs in the radial pathway (i.e., from the ambient solution into the root xylem). The details of radial water flow are less well understood than those of axial flow, however, because roots are highly complex, and the proportions of water moving in the various available pathways may be altered depending on the driving forces. The anatomy of roots changes along their length as various structures develop, mature, and, perhaps, die. Their structure can change in response to different environmental conditions. In addition, there is wide variation in structure amongst species. Despite the complexities of roots and the challenges involved in determining how water moves through them, recent progress has been made on several fronts.