Involvement of lignin and hormones in the response of woody poplar taproots to mechanical stress

Mechanical stress is a widespread condition caused by numerous environmental factors thatseverely affects plant stability. In response to mechanical stress, plants have evolved complex response pathwaysable to detect mechanical perturbations and inducing a suite of modificationsin order to improve anchorage. The response of woody roots to mechanical stresses has been studied mainly at the morphological and biomechanical level, whereas investigations on the factorstriggering these important alterations are still at the initial stage. Populus has been widely used to study the response of stem to different mechanical stresses and, since it has the first forest tree genome to be decoded, represents a model woody plant for addressing questions onthe mechanisms controlling adaptation of woody roots to changing environments. In this study, amorphological and physiological analysis was usedto investigatefactors controlling modifications in Populus nigrawoody taproots subjected to mechanical stress. Anexperimental model analyzing spatial and temporal mechanical force distribution along the woody taproot axis enabled us to compare the events occurring in its above-bending-, central bending- and below-bending-sectors. Different morphogenetic responses and local variations of lignin and plant hormones content have been observed, and a relation with the distribution of the mechanical forces along the stressed woody taproots is hypothesized. We investigated the differences of the response to mechanical stress induction during the time; in this regard, we present data referring to the effect of mechanical stress on plant transition from its condition of winter dormancy to that of full vegetative activity.