The grasping side of pea plants: a matter of learning?

At first glance, plants seem relatively immobile, stuck to the ground in rigid structures, but movement pervades all aspects of plant behavior. Here, we address the main question of whether such movements are “goal-directed” and, if so, how such capacity is acquired. To this end, we shall present two kinematical studies on pea plants searching for and grasping a potential support in the environment. We characterized the growth movement of pea plant from the germination of the seed to the grasping of the support by means of three-dimensional (3D) kinematical analysis. In one study we demonstrate the ability of pea plants to process the intrinsic features of a support (e.g., thickness) and to modulate their approaching and grasping behaviour accordingly. In another study, we explore how this process is eventually ‘learned’ during growth. The results suggest that the information acquired by the plant at a certain growth stage is communicated to the following stage. A process that continues until the plant has acquired all the necessary information to successfully grasp the support. This mechanism is suggestive of a motor learning process based on the transmission of practice-related information across growth stages. Results are discussed in the light of available theories put forward to explain how plants sense the environment and adapt their growth to the task at hand.