Mechanics of Reversible Deformation during Leaf Movement and Regulation of Pulvinus Development in Legumes

Abstract

Plant cell deformation is a mechanical process that is driven by differences in the osmotic pressure inside and outside of the cell and is influenced by cell wall properties. Legume leaf movements result from reversible deformation of pulvinar motor cells. Reversible cell deformation is an elastic process distinct from the irreversible cell growth of developing organs. Here, we begin with a review of the basic mathematics of cell volume changes, cell wall function, and the mechanics of bending deformation at a macro scale. Next, we summarize the findings of recent molecular genetic studies of pulvinar development. We then review the mechanisms of the adaxial/abaxial patterning because pulvinar bending deformation depends on the differences in mechanical properties and physiological responses of motor cells on the adaxial versus abaxial sides of the pulvinus. Intriguingly, pulvini simultaneously encompass morphological symmetry and functional asymmetry along the adaxial/abaxial axis. This review provides an introduction to leaf movement and reversible deformation from the perspective of mechanics and molecular genetics.

Nyctinastic movement in legumes: Developmental mechanisms, factors and biological significance

“…In contrast, during reversible cell deformation, such as reversible volume changes in pulvinus motor cells, the connections between the cellulose microfibrils remain largely unchanged and exhibit elastic properties (Cosgrove, 2005). The spring‐like behaviour of cellulose microfibrils in the pulvinus motor cells plays a crucial role in the deformation of extensor motor cells, and the structure of the cell‐wall matrix is essential for achieving sufficient expansion/contraction within the physiological turgor pressure range (Nakata & Takahara, 2022). The orientation of the maximal expansion rate is typically governed by the net alignment of cellulose microfibrils, which counteracts the predominant anisotropic stress (Baskin, 2005).…”

“…Changes in turgor pressure during leaf movement are caused by alterations in intracellular osmotic fluid concentration. This process involves water flux and ion concentrations, with the water flux within the cell determining the rate of cell volume change and the magnitude of the turgor pressure (Morillon et al, 2001; Nakata & Takahara, 2022). Nuclear magnetic resonance was used to investigate the distribution of water in the pulvinus of M. pudica during rapid movement.…”

Pulvinar Slits: Cellulose-deficient and De-Methyl-Esterified Homogalacturonan-Rich Structures in a Legume Motor Cell

“…Since the cellular membrane acts as a semi-permeable barrier, a change in cell volume is the result of water flux between the inside and the outside of the cell (and the vacuole) and is triggered by the difference in water potential between the two sides (Morris and Blyth, 2019; Nakata and Takahara, 2022). In inner tissues and in a microenvironment, water potential almost equals osmotic potential; cells swell when exposed to a hypotonic condition, while they contract under a hypertonic condition.…”

“…In growing cells, cell expansion is triggered by loosening of the cell wall by changing connections between cellulose microfibrils (Cosgrove, 2005). In the context of reversible deformation, the connections between cellulose microfibrils are thought to not be altered and to behave as an elastic material, with changes in osmotic potential triggering cell expansion or contraction (Nakata and Takahara, 2022). The difference of mechanical behavior suggests that cell wall properties of reversibly deforming cells, like motor cells, differ from those of growing cells.…”

Regulatory Mechanisms of Transcription Factors in Plant Morphology and Function

“…Legume leaf movement results from the deformation of pulvinar cells. Nakata and Takahara reviewed pulvinar deformation and development, the latter of which is regulated by the complex actions of TFs [ 4 ]. Rorippa aquatica changes its leaf morphology to narrow blades in response to submergence.…”