The effects of mechanical stimulation on the morphology and mechanics of maize roots grown in an aerated nutrient solution

The effects of local mechanical stimulation on local root growth was investigated in maize (Zea mays L.) growing in an aerated nutrient solution. The morphology and mechanical properties of primary nodal roots were compared between those that underwent a program of flexing and those that received no mechanical stimulation. Local mechanical stimulation had limited effects on the morphology of maize nodal roots; there was no significant effect of flexing on the diameter of primary nodal roots when compared with untreated roots. However, there were significant differences in root mass between treatments; there was a large decrease of 43% in the fresh and 41% in the dry mass of the fine roots in the flexed roots compared with the untreated roots. Surprisingly, there was only a small effect on the mass of the primary nodal roots: only at the fifth node was there a significant increase of 15% in the dry mass of flexed roots compared to those that received no mechanical stimulation. The effects of root flexure on the mechanical properties of the roots were more dramatic. Roots at both nodes 4 and 5 were significantly more rigid, stronger, and composed of a stiffer material than those that received no mechanical stimulation. After flexing, the primary nodal roots at the fifth node showed increases of 75% in the rigidity, 60% in the bending strength, and 70% in the bending modulus of the flexed roots compared to unstimulated roots. This study shows that the thigmomorphogenetic response, at least in maize roots, can be localized even down to individual roots and not just to regions of the root system.