Abstract
Fresh water is an increasingly scarce resource for agriculture. Plant roots mediate water uptake from the soil and have developed a number of adaptive traits such as hydrotropism to aid water foraging. Hydrotropism modifies root growth to respond to a water potential gradient in soil and grow towards areas with a higher moisture content. Abscisic acid (ABA) and a small number of genes, including those encoding ABA signal transducers, MIZ2/GNOM, and the hydrotropism-specific MIZ1, are known to be necessary for the response in Arabidopsis thaliana, whereas the role of auxin in hydrotropism appears to vary depending on the plant species. This review will describe recent progress characterizing the hormonal regulation of hydrotropism. Recent advances in identifying the sites of hydrotropic perception and response, together with its interaction with gravitropism, will also be discussed. Finally, I will describe putative mechanisms for perception of the water potential gradient and a potential role for hydrotropism in acclimatizing plants to drought conditions.
Highlights
Plants need to respond to a constantly changing environment and use tropisms to reposition organs for resource capture
In the interaction between hydro- and gravitropism, a clear distinction has to be drawn between plant species that depend on auxin and its transport for their hydrotropic response and those where hydrotropism is independent of development of a lateral auxin gradient
Hydrotropism research has taken a leap forward in the last few years with a number of discoveries describing the site of perception, bending mechanism and interaction with gravitropism
Summary
Plants need to respond to a constantly changing environment and use tropisms to reposition organs for resource capture. Plant roots are able to perceive a water potential gradient in their surroundings and change the direction of the root tip through differential growth in the elongation zone. Roots showing a hydrotropic response will change the growth direction of the root tip, either bending around the supporting block or towards the medium with higher water potential.
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