Insights into the chemical composition of <Emphasis Type="Italic">Equisetum hyemale</Emphasis> by high resolution Raman imaging |
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Authors: | Notburga Gierlinger Lanny Sapei Oskar Paris |
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Institution: | (1) Department of Biomaterials, Max-Planck-Institute of Colloids and Interfaces, Am Mühlenberg 1, 14424 Potsdam-Golm, Germany |
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Abstract: | Equisetaceae has been of research interest for decades, as it is one of the oldest living plant families, and also due to
its high accumulation of silica up to 25% dry wt. Aspects of silica deposition, its association with other biomolecules, as
well as the chemical composition of the outer strengthening tissue still remain unclear. These questions were addressed by
using high resolution (<1 μm) Confocal Raman microscopy. Two-dimensional spectral maps were acquired on cross sections of Equisetum hyemale and Raman images calculated by integrating over the intensity of characteristic spectral regions. This enabled direct visualization
of differences in chemical composition and extraction of average spectra from defined regions for detailed analyses, including
principal component analysis (PCA) and basis analysis (partial least square fit based on model spectra). Accumulation of silica
was imaged in the knobs and in a thin layer below the cuticula. In the spectrum extracted from the knob region as main contributions,
a broad band below 500 cm−1 attributed to amorphous silica, and a band at 976 cm−1 assigned to silanol groups, were found. From this, we concluded that these protrusions were almost pure amorphous, hydrated
silica. No silanol group vibration was detected in the silicified epidermal layer below and association with pectin and hemicelluloses
indicated. Pectin and hemicelluloses (glucomannan) were found in high levels in the epidermal layer and in a clearly distinguished
outer part of the hypodermal sterome fibers. The inner part of the two-layered cells revealed as almost pure cellulose, oriented
parallel along the fiber. |
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Keywords: | Cellulose Cell wall Confocal Raman microscopy Hemicelluloses Pectin Scouring rush Silica |
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