AUTHOR=Carmesin Cora F. , Port Fabian , Böhringer Samuel , Gottschalk Kay-Eberhard , Rasche Volker , Jansen Steven 

TITLE=Ageing-induced shrinkage of intervessel pit membranes in xylem of Clematis vitalba modifies its mechanical properties as revealed by atomic force microscopy

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1002711

DOI=10.3389/fpls.2023.1002711

ISSN=1664-462X

ABSTRACT=<p>Bordered pit membranes of angiosperm xylem are anisotropic, mesoporous media between neighbouring conduits, with a key role in long distance water transport. Yet, their mechanical properties are poorly understood. Here, we aim to quantify the stiffness of intervessel pit membranes over various growing seasons. By applying an AFM-based indentation technique “Quantitative Imaging” we measured the effective elastic modulus (<italic>E</italic><sup>effective</sup>) of intervessel pit membranes of <italic>Clematis vitalba</italic> in dependence of size, age, and hydration state. The indentation-deformation behaviour was analysed with a non-linear membrane model, and paired with magnetic resonance imaging to visualise sap-filled and embolised vessels, while geometrical data of bordered pits were obtained using electron microscopy. <italic>E</italic><sup>effective</sup> was transformed to the geometrically independent apparent elastic modulus <italic>E</italic><sup>apparent</sup> and to aspiration pressure <italic>P</italic><sub>b</sub>. The material stiffness (<italic>E</italic><sup>apparent</sup>) of fresh pit membranes was with 57 MPa considerably lower than previously suggested. The estimated pressure for pit membrane aspiration was 2.20+28 MPa. Pit membranes from older growth rings were shrunken, had a higher material stiffness and a lower aspiration pressure than current year ones, suggesting an irreversible, mechanical ageing process. This study provides an experimental-stiffness analysis of hydrated intervessel pit membranes in their native state. The estimated aspiration pressure suggests that membranes are not deflected under normal field conditions. Although absolute values should be interpreted carefully, our data suggest that pit membrane shrinkage implies increasing material stiffness, and highlight the dynamic changes of pit membrane mechanics and their complex, functional behaviour for fluid transport.</p>