Mechanical bending stress can result in cell wall strengthening and increased wood formation across root axes together with an attendant asymmetrical accumulation of phytohormones. De Zio et al. show how different mechanical force intensities act across the compressed concave and stretched convex sides of the woody bent poplar taproot.
The results show that, in contrast to the response of the poplar stem, bending stress applied to woody poplar taproots results in increased wood formation toward the concave side (compressed zone), characterized by the highest values of quantity of cambial cells, xylem thickness and lignin content. The highest quantity of lateral roots is revealed in the stretched zone of the convex side, which constitutes the site for an asymmetrical accumulation of auxin, the phytohormone responsible for triggering lignin deposition and cell wall strengthening in the concave sides.