Root-to-shoot communication for the coding of object thickness in pea plants

Plants characterized by a weak steam, such as climbing plants, need to find a potential support (i.e., a stick or a wooden trunk) to reach the greatest light exposure. Since Darwin’s observation, several studies on the searching and attachment behaviors of climbing plants have reported the unique ability of climbing plants to process different support features as to modulate their movement accordingly. Nevertheless, the strategies underlying this ability have yet to be uncovered. The present research tries to fill this gap by investigating how the interaction between the above- (i.e., stem, tendril, …) and below-ground (i.e., the root system) plant’s organs is played out in the kinematics of the approach to grasp movement. The movement of pea plants (Pisum sativum L.) toward a stimulus characterized by different thicknesses with respect to the below- and above-ground part of it (i.e., perturbed conditions) was assessed by means of three-dimensional (3D) kinematical analysis. Control conditions, in which one-thickness stimulus (i.e., thin, or thick) was presented, were also considered. Results suggest the contribution of the root system in sensing, coding, and processing below-ground information and how such information is evaluated and eventually modified at the level of the aerial part of the plant to fulfill the end-goal of the movement. Results are discussed in terms of a functional equilibrium reached through a crosstalk between the grounded and the aerial components of the plant.