Abstract
The role of xyloglucan (XG) in the cell wall of plants and its technological usability depends on several factors, pertaining to molecular structure. Therefore, the goal of this study was to evaluate the nano-structure and self-assembly of XG by atomic force microscopy (AFM). As the model, a non-modified xyloglucan from a tamarind seed (Tamarindus indica L.) was used. Samples were minimally processed, i.e., treated with low-power ultrasound and studied on the surface of mica in ambient butanol. AFM topographic images revealed rod-like nanomolecules of xyloglucan with a mean height of 2.3 ± 0.5 nm and mean length of 640 ± 360 nm. The AFM study also showed that XG chains possessed a helical structure with a period of 115.8 ± 29.2 nm. This study showed possible-bending of molecules with a mean angle of 127.8 ± 25.6°. The xyloglucan molecules were able to aggregate as cross-like and a parallel like assemblies, and possibly as rope-like structures. The self-assembled bundles of xyloglucan chains were often complexed at an angle of 114.2 ± 36.3°.
Highlights
Xyloglucan (XG) is the most abundant polysaccharide from the group of hemicelluloses in the primary cell wall of higher plants comprising of about 20 % of all constituents of dicotyledons [1]
The observation that xyloglucan molecules have a tendency to link is in line with atomic force microscopy (AFM) images of hemicelluloses obtained
The AFM study showed that xyloglucan molecules from the tamarind seed have a rectilinear, slender and rod-like structure with a mean diameter of 2.3±0.5 nm and mean length of 640± 360 nm
Summary
Xyloglucan (XG) is the most abundant polysaccharide from the group of hemicelluloses in the primary cell wall of higher plants comprising of about 20 % of all constituents of dicotyledons [1]. The nanostructure of a xyloglucan polysaccharide determines the crosslinking mechanism to cellulose microfibrils, i.e., a less substituted backbone of XG (fucosyl branching), the greater capability for binding to cellulose [5, 6]. The arrangement of XG chains contributes to a higher rigidity of the wall. This biopolymer is a heteropolysaccharide possessing the backbone composed of 1,4-β-D-glucose. Additional residues, in form 1,2-β-D galactose, may be attached to xylose, depending on the origin of xyloglucan. XG, as a cross-linking material, coats the surface of cellulose microfibrils, some of them may penetrate and disrupt the microcrystalline parts of cellulose molecules [10]
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