A cell changes volume
Water-storage cells decrease in volume during dehydration. In some succulents, their walls form regular folds. After water is restored, the cells can expand again. This reversibility allows the storage function to be combined with mechanical continuity of the tissue. The phenomenon has been described most thoroughly in the hydrenchyma of selected cacti and aloes. [Fradera-Soler et al. 2022, Fradera-Soler i wsp. 2022 p. 2291, 2295–2300]
The primary wall surrounds the cell membrane and bears forces generated by turgor. Cellulose microfibrils interact with hemicelluloses, pectins and proteins. Pectins form a hydrated component of this structure. Changes in their distribution or properties can influence stiffness and deformability. Mechanical function emerges from the arrangement of the components as a whole. [Fradera-Soler et al. 2022, Fradera-Soler i wsp. 2022 p. 2291, 2295–2300]
Elasticity and folding
An elastic wall allows a cell to release a substantial amount of water with a relatively small change in pressure. This helps maintain turgor, the pressure exerted by the cell contents on their surroundings. Tissues with high hydraulic capacitance can gradually supply neighbouring regions. Their capacity to change volume is part of water management, alongside transport and regulation of dissolved substances. [Fradera-Soler et al. 2022, Fradera-Soler i wsp. 2022 p. 2291, 2295–2300]
Folding differs from random structural damage to the cell. In the tissues described, a repeatable deformation pattern accompanies continued contact between wall and membrane. The review authors associate this response with reduced mechanical damage during shrinkage. Recovery of volume concerns living tissue whose degree of dehydration remains within its tolerance range. [Fradera-Soler et al. 2022, Fradera-Soler i wsp. 2022 p. 2291, 2295–2300]
Wall composition and a mechanistic model
In the reviewed studies of Aloe helenae and Aloe vera, dehydration was accompanied by changes in the detection of pectic components in hydrenchyma walls. Changes in the location of mannans, polysaccharides associated with walls and storage, were also observed. The authors related these findings to wall remodelling during drought. The review presents them as evidence informing a mechanism whose detailed regulation remains poorly understood. [Fradera-Soler et al. 2022, Fradera-Soler i wsp. 2022 p. 2291, 2295–2300]
The proposed model assumes spatial differences in wall compliance. Softer regions could determine folding zones, while the remaining regions maintain mechanical continuity. This is a hypothesis explaining the repeatable geometry of deformation. Confirmation requires live-tissue imaging combined with measurements of composition and mechanical properties. An image of a fold reveals its shape but does not identify every process that produced it. [Fradera-Soler et al. 2022, Fradera-Soler i wsp. 2022 p. 2291, 2295–2300]
Parenchyma and supporting tissues
A water-storage organ also contains conducting and supporting tissues. In some succulents, their secondary walls have banded thickenings. In the systems described, this structure constrains the direction of shrinkage and may help maintain conducting pathways. Deformable parenchyma and reinforcing elements thus form different parts of the same organ. Their relative proportions vary among species. [Fradera-Soler et al. 2022, Fradera-Soler i wsp. 2022 p. 2291, 2295–2300]
The 2022 review identifies uneven coverage in the available evidence. Folding has been described in detail in only a small fraction of plants, and its distribution among succulents requires broader study. A wrinkling leaf provides a starting point for investigating water mobilisation. Identifying the specific mechanism requires tissue-level evidence, and comparing species resistance also requires information about the duration and conditions of dehydration. [Fradera-Soler et al. 2022, Fradera-Soler i wsp. 2022 p. 2291, 2295–2300]
Prepared from the full texts of the supplied publications. The original diagram illustrates functional relationships and is not drawn to scale.
Elastic and collapsible: current understanding of cell walls in succulent plants
Fradera-Soler M., Grace O. M., Jørgensen B., Mravec J., Elastic and collapsible: current understanding of cell walls in succulent plants, Journal of Experimental Botany, 2022, 73(8):2290-2307, doi: 10.1093/jxb/erac054
Review of succulence, wall biomechanics and cell folding during dehydration. It distinguishes observations from hypothetical regulation of wall remodelling.