Root hydrotropism: An update

Abstract

While water shortage remains the single-most important factor influencing world agriculture, there are very few studies on how plants grow in response to water potential, i.e., hydrotropism. Terrestrial plant roots dwell in the soil, and their ability to grow and explore underground requires many sensors for stimuli such as gravity, humidity gradients, light, mechanical stimulations, temperature, and oxygen. To date, extremely limited information is available on the components of such sensors; however, all of these stimuli are sensed in the root cap. Directional growth of roots is controlled by gravity, which is fixed in direction and intensity. However, other environmental factors, such as water potential gradients, which fluctuate in time, space, direction, and intensity, can act as a signal for modifying the direction of root growth accordingly. Hydrotropism may help roots to obtain water from the soil and at the same time may participate in the establishment of the root system. Current genetic analysis of hydrotropism in Arabidopsis has offered new players, mainly AHR1, NHR1, MIZ1, and MIZ2, which seem to modulate how root caps sense and choose to respond hydrotropically as opposed to other tropic responses. Here we review the mechanism(s) by which these genes and the plant hormones abscisic acid and cytokinins coordinate hydrotropism to counteract the tropic responses to gravitational field, light or touch stimuli. The biological consequence of hydrotropism is also discussed in relation to water stress avoidance.

Growing Out of Stress: The Role of Cell- and Organ-Scale Growth Control in Plant Water-Stress Responses

“…In line with this hypothesis, water-stressed roots also contain degraded amyloplasts (Takahashi et al, 2003;Nakayama et al, 2012;Cassab et al, 2013), which may be important for osmotic adjustment and presumably also makes them less responsive to gravity.…”

ABA mediates PEG-mediated premature differentiation of root apical meristem in plants

“…For example, plant roots can sense soil moisture gradients and grow toward to a source of water (referred as hydrotropism). 1 Plants also can modify their root system architecture to adapt themselves to the water stress conditions. We have previously shown that plants are able to stimulate lateral root development with enhanced stress tolerance through programmed cell death of the root apical meristem (RAM) of the primary roots under severe water stress.…”

Beyond the Barrier: Communication in the Root through the Endodermis

“…The root system, which is directly in contact with soil particles, can integrate environmental cues to adjust its development in order to optimize nutrient (Péret et al, 2011;Lynch, 2013) and water uptake (Cassab et al, 2013;Lynch, 2013;Bao et al, 2014) or avoid regions of high salinity (Galvan-Ampudia et al, 2013). Once anchored in the soil, roots must deal with the constraints of their local environment and develop specific barriers to balance uptake of nutrients, water, and interactions with symbionts with protection against detrimental biotic and abiotic factors.…”