Optimization of water foraging by plants is partially achieved by the ability of roots to direct growth towards high water potential, a phenomenon termed hydrotropism. In contrast to gravitropism and phototropism, which require auxin redistribution, as suggested by the Cholodny-Went theory, hydrotropism is not mediated by the phytohormone auxin, which raises questions about the mechanism underlying this tropic response. Here we specify the open questions in this field of research and discuss the possible interactions of abscisic acid, calcium and reactive oxygen species as part of a dynamic system of sensing water potential in the root tip, transmission of the signal to the root elongation zone and promoting root curvature towards water. We conclude that root hydrotropism is mediated by inter-cellular signals that are not explained by the Cholodny-Went theory.
Bibliographical noteFunding Information:
The research of hydrotropism in the lab of H.F. is supported by the I-CORE Program of the Planning and Budgeting Committee and The Israel Science Foundation (grant No 757/12 ). We thank Professor Dudy Bar-Zvi for critical reading of the manuscript.
© 2016 Elsevier Ireland Ltd
- Abscisic acid (ABA)
- Reactive oxygen species (ROS)
- Water potential