Abstract
Equisetum species are primitive vascular plants that benefit from the biogenesis of silica bio-organic inclusions in their tissues and participate in the annual biosilica turnover in local eco-systems. As means of Equisetum reproduction and propagation, spores are expected to reflect the evolutionary adaptation of the plants to the climatic conditions at different times of the year. Combining methods of Raman and scanning electron microscopy and assisted with density functional theory, we conducted material spatial-spectral correlations to characterize the distribution of biopolymers and silica based structural elements that contribute to the bio-mineral content of the elater. The elater tip has underlying skeletal-like structural elements where cellulose fibers provide strength and flexibility, both of which are necessary for locomotion. The surface of the elater tips is rich with less ordered pectin like polysaccharide and shows a ridged, folded character. At the surface we observe silica of amorphous, colloidal form in nearly spherical structures where the silica is only a few layers thick. We propose the observed expansion of elater tips upon germination and the form of silica including encapsulated biopolymers are designed for ready dispersion, release of the polysaccharide-arginine rich content and to facilitate silica uptake to the developing plant. This behavior would help to condition local soil chemistry to facilitate competitive rooting potential and stem propagation.
Highlights
The occurrence of silica in algae (Brunner et al, 2009), simple animals (Mann et al, 1983) and in plants (Sachs, 1862; Lewin and Reimann, 1969; Page, 1972; Hodson et al, 2005) are important examples of bio-mineralization in evolution
Using the results of quantum chemistry and experimental Raman spectroscopy to correlate the presence of different chemical species at the elater surface, we show differences between Raman microscopy images reconstructed for selected vibrations, while the intensities of the Raman images are scaled to be equal
Our Raman microscopy results suggest that; (d) silica is deposited in its amorphous form in thin layered structures; (e) there is a relative increase of silica at the sites of spherical containers; (f) pectin- and glucomannan-like glycosides may have some preference in the interior of the spherical containers; (g) the spherical containers are attached at the surface of paddle structures where cellulose-like planar bio-organic components dominate and where lignin contributions are diminished
Summary
The occurrence of silica in algae (i.e., diatoms) (Brunner et al, 2009), simple animals (i.e., sponges) (Mann et al, 1983) and in plants (Sachs, 1862; Lewin and Reimann, 1969; Page, 1972; Hodson et al, 2005) are important examples of bio-mineralization in evolution. Silica may accumulate in pith (stem), cortex (stem or root), mesophyll (leaves) and vascular tissues of plants (Lewin and Reimann, 1969). (commonly known as horsetail) are ancient examples of living vascular plants (Page, 1972). It has been reported that Equisetum spp. take up mono-silicic acid from the soil to accumulate silica in their tissues (Timell, 1964; Grégoire et al, 2012). The genus benefits from a broad global distribution and yet can be considered as an invasive and persistent weed.
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