Abstract Detail

Development and Structure

Sleboda, David [1], Geitmann, Anja [2], Sharif-Naeini, Reza [1].

Structural control of rapid pulvinus movement in Mimosa pudica.

Touch the sensitive plant Mimosa pudica and it rapidly changes shape, folding its leaves to deter herbivores and scare off pests. This and other feats of rapid plant movement have fascinated scientists for centuries. Unlike animals, plants do not have muscles and instead use quick changes in cell turgor pressure to effect motion. The physiological mechanisms underlying rapid turgor changes are well described; however, how plants translate these changes into coordinated, directed movement of whole organs remains unclear. Here we explore the biomechanics of pulvinus organs, joint-like motor organs that power movement in Mimosa and other fast-moving plants. Using flexible silicone rubber, we built a soft hydraulic actuator that mimics pulvinus structure and bending mechanics. Adding circumferential hoop reinforcements to the hydraulic "cells" of this actuator dramatically improved its bending performance, and from this observation, we hypothesized that biological pulvinus organs may contain functionally analogous reinforcements that guide cell shape during rapid turgor changes. To test this, we used osmotic baths to swell live, isolated pulvinus organs and looked for nonuniform changes in their 3D shape. To probe the scale at which reinforcement occurs, we repeated this experiment on organs skinned of their enveloping epidermis and on sections of hydraulic cells isolated from the pulvinus core. Consistent with the behavior of reinforced actuator cells, osmotic swelling resulted in longitudinal extension with little or no radial expansion in all pulvinus organ preparations. Organs with an intact epidermis and sections of hydraulic cells each increased in length by approximately 20% with negligible changes in radius. Organs skinned of their epidermis elongated a similar amount but were prone to unstable outward bowing of their hydraulic tissues. These results suggest that pulvinus organs increase the speed and efficiency of their movements by regulating turgor-induced shape changes at both cell- and whole-organ levels. Specialized cell wall and epidermis morphologies revealed by electron microscopy support this interpretation. Our findings provide new insights into plant motor strategies, underscore the hierarchical, emergent nature of biomechanical systems, and highlight design principles that can inform the development of biologically inspired soft actuators.

1 - McGill University, Physiology, 3649 Promenade Sir William Osler, Bellini Life Sciences Complex, Room 173, Montreal, QC, H3G 0B1, Canada
2 - McGill University, Plant Science, 21111 Lakeshore, R2-036, Ste-Anne-de-Bellevue, QC, H9X 3V9, Canada

Keywords:
pulvinus
biomechanics
Mimosa pudica
cell wall
epidermis
Thigmonasty
morphology.

Presentation Type: Oral Paper
Session: DS3, Development and Structure III
Location: /
Date: Thursday, July 22nd, 2021
Time: 2:00 PM(EDT)
Number: DS3016
Abstract ID:33
Candidate for Awards:None