A fast method to prepare microslides of wood in advanced stages of decay

in IAWA Journal
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ABSTRACT

Biologically degraded wood in advanced stages of decay has a very soft and brittle structure that causes many problems during sectioning. Embedding wood specimens in different kinds of media ensures preparation of good quality microsections, but the preparation time is very long. The proposed method does not only have a reduced preparation time but also minimizes costs and consumption of chemicals while improving stabilization of the specimen and enhancing the quality of sections. The crux of the method is application of a reinforcing layer of transparent nail polish gel on a dry specimen that has been only stabilized (not embedded) with PEG 1500 medium. The gel is applied on a specimen in two layers just before sectioning. The first layer infiltrates the specimen sufficiently deep to fill the lumens and cell walls and allows preparation of thin sections from decayed wood. The second layer reinforces the section and allows better handling. Subsequently, the reinforcing and embedding layers are removed using pure acetone. This innovative method has so far been successfully tested on specimens that were degraded by the fungus Pleurotus ostreatus (mass loss 55% and 83%) and the fungus Phaeolus schweinitzii (mass loss 45%), taken from Fagus sylvatica and Pinus sylvestris species, a hardwood and softwood respectively with contrasting wide vessels and narrow tracheids.

A fast method to prepare microslides of wood in advanced stages of decay

in IAWA Journal

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References

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Figures

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    Preparation procedure of sections. – a: Sample of Fagus sylvatica L. decayed by Pleurotus ostreatus. – b: Sample of Pinus sylvestris L. decayed by Phaeolus schweinitzii. – c: Wooden block bordered by adhesive tape. – d: Placement of decayed specimen on wooden block in the required anatomical direction. – e: The specimen stabilized in PEG 1500 medium. – f: Application of embedded and reinforced gel layers on trimmed specimen surface. – g: Sectioning of specimens in a sledge microtome. – h: Trimming the excess gel margins by a razor blade. – i: Gluing the section on a slide with Mayer’s albumin adhesive. – j: Removing of surplus adhesive by pressing absorbent paper on the section.

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    Tissues of Fagus sylvatica L. affected by white-rot fungus Pleurotus ostreatus. – a & c: Cross sections with mass loss of 83%. Arrows point to missing degraded zones released from the sections. – b & d: More coherent cross sections with mass loss of 55%. — a–c: Blue stained residues of lignin in cell walls and middle lamellae. The birefringence points to presence of cellulose in cell walls. – d: Simultaneous degradation of lignin and cellulose in cell wall layers S2 and S1. – e: Longitudinally and radially oriented hyphae network in fibres, vessels and parenchyma cells of rays. All sections were stained by Toluidine Blue O, sections a–c were observed under polarised light. — Scale bars for a & b: 100 μm; c: 20 μm; d: 10 μm; e: 200 μm.

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    Tissues of Pinus sylvestris L. affected by brown-rot fungus Phaeolus schweinitzii (estimated mass loss of 45%). – a–c: The sections show the heterogeneous decomposition of cellulose (dark-brown or blue colour) and lignin (white coloured birefringence) in its various parts. Arrows point to missing degraded zones, released from the sections. — a & b: Unstained cross sections. – c: Toluidine Blue O stained radial section. — Scale bars for a: 200 μm; b & c: 500 μm.

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