Plant surfaces and interfaces


Plant Surfaces and Interfaces: Lignin, Suberin and Cutin


As plants evolved from aquatic to terrestrial environment complex phenolic compounds (lignin) and natural polyesters (cutin, suberin) have played a major role by building hydrophobic surfaces and interfaces. The deposition of lignin as an additional interface between the cellulose microfibrils and hemicelluloses has been essential for the functioning of the developed water conducting elements (xylem) and for mechanical strength to stand upright and expand significantly in body size. The outermost surfaces had to be adapted to regulate water loss, which has been achieved by suberisation (stem, root) and cutinisation (leaf). Although general principles on the three compounds are known, they are the least understood plant polymers due to their high variability in amount and structure and still unresolved questions regarding polymerisation. Adaptation to survive in the great variety of habitats has resulted in quite diverse body plans that require highly specialized tissues with distinct properties and functions. These are achieved by changing composition and structure at the different hierarchical levels (mm-μm-nm) and there is still a huge knowledge gap on the microchemistry and nanostructure of the native cell walls and its interfaces and surfaces.
We will bridge this gap by application of non-destructive Raman imaging and Atomic force microscopy (AFM). Raman imaging gives access to the chemical composition on the micro level and AFM complements by elucidating nanostructure and-mechanics. Every Raman image is based on thousands of spectra, each a position resolved (0.3μm) molecular fingerprint of the cell wall. Currently only a part of the chemical and structural information in the Raman signature is extracted and we aim at maximising the knowledge gain by applying new multivariate data analysis approaches. To drive the chemical information below the diffraction limit of light for probing tiny plant interfaces and surfaces we will explore the challenging tip-enhanced Raman spectroscopy (TERS) technique.
With these sophisticated in-situ approaches we will 1) follow the lignification spatially resolved within the native cell wall to tackle unresolved questions around lignin polymerisation, 2) reveal the chemistry and structure of tracheid and vessel walls on the micro and nano level (including vessel surface and pit membranes) and its implications on hydraulic and mechanical properties 3) investigate the microchemistry and nanostructure of suberized and cutinized layers and its relation to barrier properties, 4) additionally assess the impact of water stress as drought is becoming more and more a limiting factor for tree growth. New insights into the micro and nano distribution and composition of the plant polymers and as affected by drought stress will be gained and important structure-function relationships revealed. This will break new scientific grounds in the field of plant physiology (plant hydraulics, lipophilic barriers) and wood science (lignification, material properties) and have an impact on optimised plant feedstock development (forestry, agriculture, breeding, genetic engineering) and
utilisation (biorefinery, pulp and paper, biopolymers) and probably inspire new biomimetic approaches.

This research is conducted under the FWF START Project grant Y-728-B16.