Insights into the chemical composition of Equisetum hyemale by high resolution Raman imaging

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 m) 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 diVerences in chemical composition and extraction of average spectra from deWned regions for detailed analyses, including principal component analysis (PCA) and basis analysis (partial least square Wt 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 siliciWed 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 Wbers. The inner part of the two-layered cells revealed as almost pure cellulose, oriented parallel along the Wber.

Raman Imaging of Lignocellulosic Feedstock

“…In the Raman spectrum the region between 860-825 cm -1 corresponds to equatorial anomeric H (α-anomers and α-glycosides), whereas the band at about 900-880 cm -1 corresponds to axial anomeric H (β-anomers and β-glycosides) [147]. The sharp Raman band between 860 and 854 cm -1 is characteristic for pectin and shows no overlap with the other plant cell wall polymers and can therefore be used as a marker band in the imaging approach [148,149]. Furthermore the exact position of this band is sensitive to the state of uronic carboxyls and to O-acetylation thus providing insight into pectin structure; decreasing with methylation (min.…”

“…By calculating the integral of the bands in the Raman spectra of plant cell walls the distribution of different molecular structures can be imaged on the micron-level [148,149,167,183]. Figure 5A shows an example of imaging water uptake of cell walls in young poplar wood (Populus nigra x Populus deltoids) by plotting the integral of the OH stretching vibration.…”

Quantifying Bio-Engineering: The Importance of Biophysics in Biofuel Research

“…Raman imaging of Arabidopsis thaliana, one of the most important model plants, was recently demonstrated (Schmidt et al, 2009). Principal component analysis (PCA) and partial least square (PLS) modeling can be incorporated in image analysis to provide a more detailed comparison of cell wall compositions at different mapped regions (Gierlinger et al, 2008b). Raman imaging technique was also used to compare lignification in wild type and lignin-reduced 4-coumarate-CoA ligase (4CL) transgenic Populus trichocarpa stem wood (Schmidt et al, 2009).…”

Silicon in banana plants: uptake, distribution and interaction with the disease fusarium wilt

“…Silicon uptake is more prevalent in evolutionary basal plants (Ma and Takahashi, 2002c). The highest silicon content is found in the Equisetacea, a genus of plants often referred to as living fossils (Gierlinger et al, 2008). Other early or primitive plants appear to be silicon accumulators, such as the 'fern ally" Selaginella emmeliana (Dengler and Lin, 1980).…”

“…Plants absorb silicon from the soil at differing rates depending on genotype, its concentration in the soil and environmental conditions, resulting in plant dry weights of silicon ranging from 0.1 to 10% (Epstein, 1994). Horsetails (Equisetum hyemale) are the highest described silicon accumulating vascular plants with up to 25% plant weight being silicon (Gierlinger et al, 2008). In rice (Oryza sativa), silicon is present at higher concentrations than the essential macronutrients nitrogen, phosphorus and potassium (Epstein, 1994;Epstein, 1999).…”