How plant hormones influence the growth of roots?

The length of plant roots is controlled by hormones.


Roots are the important underground part of all vascular plants. It continually provides the stems and leaves with water and dissolved minerals.

Besides being essential for reaching water and nutrients, the roots are essential for interacting and communicating with microorganisms in the soil. A long root enables the plant to reach deeper, more humid soil layers, for example, during drought. A shallower root with many root hairs is good for phosphate uptake, as phosphate is mostly found in the upper soil layers.

The dynamic change in plants’ root growth assumes a significant part in their adjustment to soil conditions. Contingent upon the location, nutrients or moisture can be found in higher or lower soil layers. This is the reason, depending upon the situation, a short or a long root is advantageous.

Caroline Gutjahr, Professor of Plant Genetics at the Technical University of Munich (TUM), and her team investigate how plant hormones influence roots’ growth.

Scientists found that the protein called SMAX1 acts as a molecular brake for ethylene production.

Ethylene is a plant hormone that is considered to trigger or accelerate the ripening of numerous fruits and vegetables; however, it can likewise trigger different plants’ processes. If the plant produces less of the gaseous hormone, it is stimulated to grow long roots and short root hairs.

Activating the so-called karrikin signaling pathway could remove the suppressor “SMAX1”. This switches on the production of ethylene, resulting in short primary roots and long root hairs.

For the first time, scientists successfully identified a molecular process that is switched on by the karrikin signaling pathway triggered by another hormone. They also show a molecular mechanism by which this signaling pathway regulates a developmental process in plants.

Gutjahr said“Surprisingly, this mechanism has a significant impact on the roots of the legume Lotus japonicus, the model plant for peas, beans, and lentils, on which we conducted our research.”

“We observed a much weaker influence in the roots of another model plant, Arabidopsis thaliana or thale cress, which is related to cabbage plants.”

“This shows that the diversity of plants is not only reflected in their appearance, but also the effect of their molecular triggers on growth.”

“If we understand more precisely how root growth is regulated at the molecular level and in coordination with environmental stimuli, we can cultivate crops that are better able to cope with unfavorable environmental conditions and thus produce yield even under stress.”

“That’s the reason we are investigating how the identified hormone signaling pathways (karrikin and ethylene signaling) react to different environmental conditions.”

Scientists want to discover how these two signaling pathways collaborate with the sensors that allow plants to perceive various environmental influences to adjust root growth to benefit plant survival and yield.

Journal Reference:
  1. Samy Carbonnel et al. The karrikin signaling regulator SMAX1 controls Lotus japonicus root and root hair development by suppressing ethylene biosynthesis. DOI: 10.1073/pnas.2006111117


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