The coding of object thickness in plants: When roots matter.

Abstract

Tendrils are clasping structures used by climbing plants to anchor and support their vines that coil around suitable hosts to achieve the greatest exposure to sunlight. Although recent evidence suggests that climbing plants are able to sense the presence of a potential stimulus in the environment and to plan the tendrils' movements depending on properties such as its thickness, the mechanisms underlying thickness sensing in climbing plants have yet to be uncovered. The current research set out to use threedimensional kinematical analysis to investigate if and in what way the root system contributed to thickness sensing. Experiment 1 was designed to confirm that the movement of the tendrils of pea plants (Pisum sativum L.) is planned and controlled on the basis of stimulus thickness when the stimulus is inserted into the substrate. Experiment 2 was designed to investigate what happens when the stimulus is lifted to the ground so as to impede the root system from sensing it. The results confirmed that tendrils' kinematics depend on thickness when the stimulus is available to the root system but not when it is unavailable to it. These findings suggest that the root system plays a pivotal role in sensing the presence and the thickness of a stimulus and that the information perceived affects the planning and the execution of the climbing plants' reach-to-grasp movements.

Kinematic Evidence of Root-to-Shoot Signaling for the Coding of Support Thickness in Pea Plants

“…In addition, it took more time for the tendrils to reach peak velocity and the maximum aperture when the support was thinner. Likewise, the maximum distance between the tendrils is significantly greater for thinner with respect to the thicker supports [20][21][22][23]. This phenomenon can be explained by the fact that reaching and grasping thicker supports is more energy-consuming for plants than grasping thinner ones.…”

“…Evidence from laboratory settings has further elucidated the effects of the thickness of a support by using kinematics to characterize the movements of the Pisum sativum L. (from now on P. sativum) [20][21][22][23][24]. Guerra and colleagues [22], for example, demonstrated that the P. sativum plant can perceive a support and modulate the kinematics of the tendrils' velocity and aperture depending on the thickness of the support.…”

“…Although both ecological and laboratory findings have provided data regarding the relationship between the behavior of climbers and support thickness, the mechanisms underlying thickness coding and processing remain obscure [20][21][22][23]. A variety of hypotheses based on the perceptual abilities of plants have been put forward [26].…”

“…The pivotal importance of the root system for coding the thickness of the support has been decisively revealed in a recent study focusing on P. sativum plants [23]. One experiment investigated the movement of tendrils as it leaned towards a support inserted into the substrate.…”

“…We would thus expect to see differences between the perturbed and the control conditions because the thickness for the below-ground part of the support used for the perturbed conditions differed from the thickness of the support used for the control conditions. Remember that the movement of P. sativum plants towards supports of different thicknesses are characterized by specific kinematic signatures [20][21][22][23].…”