Most of the plants grown in labs are cultivated on a gelatinous medium, not soil. Although nutritious, this homogeneous medium is usually a poor substitute for soil, where water and nutrients are unevenly distributed. But new research shows that plants are able to sense water availability differences in the soil microenvironment and adjust root growth in response to them.
The research team, which included Malcolm Bennett of the University of Nottingham and King Saud University, noted that roots consistently branched into the growth medium instead of straight out into the air. However, when the roots grew into the medium, rather than along its surface, they branched evenly around their circumference, says the study published in PNAS1.
Using X-ray microscale computed tomography, the team observed maize roots growing in soil and found uniform branching towards water pockets around the roots. However, roots adjacent to an air pore on one side only branched from the side in contact with wet soil.
The direction that roots branch out into is not determined by physical contact with the soil, but by differences in water availability. These differences lead to local changes in the synthesis, signalling and transport of the plant hormone auxin, which plays a central role in initiating root branching.
“We have discovered that plant roots can sense small differences in water availability across their diameter,” says Bennet. “Identifying the genes and signals that control this process will open up new possibilities to improve water and nutrient foraging in crops.”
Bao, Y. et al. Plant roots use a patterning mechanism to position lateral root branches toward available water. Proc. Natl Acad. Sci. USAdoi:10.1073/pnas.1400966111 (2014).