Unravelling the response of poplar (Populus nigra) roots to mechanical stress imposed by bending

Abstract

Mechanical stress is a widespread environmental condition that can be caused by several factors (i.e. gravity, touch, wind, soil density, soil compaction and grazing, slope) and that can severely affect plant stability. In response to mechanical stress and to improve their anchorage, plants have developed complex mechanisms to detect mechanical perturbation and to induce a suite of modifications at anatomical, physiological, biochemical, biophysical and molecular level. Although it is well recognized that one of the primary functions of root systems is to anchor the plant to the soil, root response to mechanical stresses have been investigated mainly at morphological and biomechanical level, whereas investigations about the molecular mechanisms underlying these important alterations are still in an initial stage. We have used an experimental system in which the taproot poplar seedlings are bent to simulate mechanical perturbation to begin investigate the mechanisms involved in root response to mechanical stress. The results reported herein show that, in response to bending, the poplar root changes its morphology by emitting new lateral roots, and its biomechanical properties by increasing the root biomass and lignin synthesis. In addition, using a proteomic approach, we found that several proteins involved in the signal transduction pathway, detoxification and metabolism are up-regulated and/or down-regulated in the bent root. These results provide new insight into the obscure field of woody root response to mechanical stress, and can serve as a basis for future investigations aimed at unravelling the complex mechanism involved in the reaction of root biology to environmental stress.

Key words:

• Root system
• mechanical stress
• poplar
• Populus nigra
• woody root

Acknowledgements

We thank Antonio Montagnoli, for his help with the experimental set up, and Jean Gilder for text editing. This work was funded by the Italian MUR (Ministero Università e Ricerca, Progetti di di Rilevanza Nazionale, PRIN, 2005). This work was carried out in the context of the COST Action E38, financed by the European Commission.