In view of global change and strong water demand from intensive agriculture, water deficit is now recognized as the abiotic stress that affects the most crop productivity and quality. Several Mediterranean regions are already under severe risk of drought, extreme temperatures, and other types of abiotic stress linked to water availability (e.g. flooding or salinity). Thus, understanding how plants use water for optimal biomass production has become a fundamental issue worldwide and, particularly, in Europe.
Plants are sessile organisms that cannot escape from environmental constraints and, as a result, have evolved numerous adaptive responses at molecular, cellular and physiological levels to cope with environmental stresses. Plants first respond to water deficit by stomatal closure together with rapid changes in root water permeability. On the long term, plants adjust their root growth to optimize their capacity to take up soil water.
Water uptake by roots is first determined by their architecture, which results from root growth and branching and underlies root ability to explore the soil. A second crucial component is the hydraulics of the root cells and tissues, that is, their intrinsic permeability to water. The cell hydraulics is determined by water channel proteins named aquaporins which facilitate water transport across cell membranes. Water deficit exerts deep effects on both root cellular hydraulics and root architecture. These effects are central for the plant’s adaptation to its environment allowing optimization of water uptake under developing drought conditions. Even though some molecular mechanisms have been recently described, there is no understanding of their integration at whole root level. This question was central throughout the DROUGHTROOT project.
The main aim of DROUGHTROOT was to understand how water deficit alters the ability of the plant root system to acquire water, by considering effects on both root hydraulics and root growth and development. These effects were addressed from an elementary developmental process, lateral root (LR) formation, up to whole root architecture. The molecular and cellular mechanisms involved were investigated in the frame of two specific questions:
- How do water availability, hormones such auxin and abscisic acid (ABA), and aquaporins interact during LR development?
- How effects of hormones on root growth and hydraulics are integrated in the whole root under water deficit conditions?
