Mechanical characterisation of the developing cell wall layers of tension wood fibres by Atomic Force Microscopy

Abstract

Trees generate mechanical stresses at periphery of stem and branches to improve their strength and to control the orientation of their axes. This key factor in the biomechanical design of trees, named "maturation stress", occurs in wood fibres during cellular maturation when their secondary cell wall thickens. In this study, the spatial and temporal stiffening kinetics of the different cell wall layers were recorded during fibre maturation on a sample of poplar tension wood using atomic force microscopy. The thickening of the different layers was also recorded. The stiffening of the CML, S 1 and S 2 -layers was initially synchronous with the thickening of the S 2 -layer and continued a little after the S 2 -layer reached its final thickness as the G-layer began to develop. In contrast, the global stiffness of the G-layer, which initially increased with its thickening, was close to stable long before it reached its final maximum thickness. A limited radial gradient of stiffness was observed in the G-layer, but it decreased sharply on the lumen side, where the new sub-layers are deposited during cell wall thickening. Although very similar at the ultrastructural and biochemical levels, the stiffening kinetics of the poplar G-layer appears to be very different from that described in maturing bast fibres.

Computational modeling of cambium activity provides a regulatory framework for simulating radial plant growth

“…Notably, staining intensities were approximately half as strong compared to cells of the surrounding tissue ( Figure 4—figure supplement 2 ). Expecting that staining intensities correlate with cell wall stiffness and by also taking into account results obtained previously by atomic force microscopy of the cambium region ( Arnould et al, 2022 ), we assumed that cambium stem cells are half as stiff as surrounding cells and integrated this feature into our model by expanding VirtualLeaf to allow for the integration of cell-type specific wall stiffness (see Supporting Information ‘VirtualLeaf Simulations’ for details). We implemented this information in the Hamiltonian operator, which is used to approximate the energy of the system and takes both turgor pressure and cell wall resistance into account.…”

Maturation Stress and Wood Properties of Poplar (Populus × euramericana cv. ‘Zhonglin46’) Tension Wood

“…Very few studies report on the relationship between growth stress and wood properties at the nanometer level of tension wood. Nano-indentation can be used to characterize mechanical properties of wood such as indentation modulus and stiffness of the cell wall [21][22][23][24].…”