Cellular UV Microspectrophotometric Investigation of Sapelli Heartwood (Entandrophragma cylindricum Sprague) from Natural Provenances in Africa

Abstract

Summary The colour of Sapelli heartwood (Entandrophragma cylindricum Sprague) is variable depending on habitat. In recent years an unusual pinkish-brown colour has been observed in commercial sawn timber of this species from Central Africa. Initial studies of Sapelli heartwood samples from various provenances have furthermore demonstrated pronounced differences in its decay resistance. Heartwood extractive composition varies considerably between provenances. Samples of Sapelli heartwood from the Central African Republic (RCA) contained 6.4% by weight of extractives compared with 12.5% for those from Cameroon and four other provenances investigated. UV microspectrophotometric analysis of heartwood extractives was used to localise phenolic extractives within wood cell walls and to identify their distribution at tissue level. The S2 and S3 wall layers of vessels and fibres in the heartwood were discriminated from sapwood by their high concentration of non-lignin phenolic extractives. These extractives in the cell walls were also found to be variable. As UV absorption properties show, the vessel and fibre secondary walls of Cameroon heartwood had a considerably higher concentration of extractives in comparison with samples from the RCA. In sapwood, the UV absorption levels for the fibre S2 layer and the vessel S3 layer were independent of the extraction procedure, suggesting the phenolic extractives in this part of the trunk were in low concentrations. Furthermore it is suggested that polyphenols constitute part of the cell wall matrix. The non-extractable phenolic content was found to be independent of provenances as demonstrated by wood from Cameroon and the RCA. The natural durability of Sapelli heartwood against fungal decay appears to be dependent on the extractive composition and on their concentration in the fibre tissue.

Tensile growth stress and lignin distribution in the cell walls of yellow poplar, Liriodendron tulipifera Linn.

“…Decreasing UV absorption reflects decreasing lignin content Goring 1970a, 1970b;Nakashima et al 1997;Donaldson et al 1999;Gindl et al 2000;Kleist and Bauch 2001;Sander and Koch 2001;Suzuki and Itoh 2001). With increasing tensile released strain, the UV absorption, and therefore the lignin content, of the secondary wall decreased (Table 2).…”

Microspectroscopy as applied to the study of wood molecular structure

“…The main lignin UV absorbance peak is found around 280 nm and depends upon the delocalised p electron system in the aromatic rings (Kleist and Bauch 2001). The position and the intensity of this peak reflect the contents of the different monomers within the lignin, that is, syringyl (S, two methoxyl (MeO) groups per aromatic ring), guaiacyl (G, one MeO group per ring) and p-hydroxyphenyl (H, no MeO groups on the ring).…”

“…As UV spectra from wood consist of broad and overlapping composite peaks, quantification attempts should be carried out with caution, as peaks may contain absorbencies unrelated to the topochemical information of interest. Peaks due to non-lignin polyphenols may for example overlap with lignin (Kleist and Bauch 2001;Watanabe et al 1997Watanabe et al , 2004.…”

Effect of extractions on dynamic mechanical properties of white mulberry (Morus alba)

“…White mulberry has quite important content of phenolic extractives [30]. In some woods, polyphenols can form part of the fiber cell wall matrix [31], while in some other woods, they may be either preferentially in vessels, parenchyma walls [32], or too much condensed to enter the cell wall substance [33]. In the later hypothesis, ME might have removed some lumen deposits, resulting in a lower ratio between changes in tand L and extraction yield.…”

“…Backman and Lindberg [1] stated that, for softwood, in tensile test latewood contributes mostly to the response in tangential direction while most of the strain occurs in early wood in radial direction. In mulberry, a ring-porous hardwood, the response in radial tension tests would more involve vessels and rays, whose cell walls are thinner, but are also susceptible to contain higher proportions of extractives [31,32,38]. Thus, the very high change in tand R after ME extraction (&50%) could express a bigger modification of rays and vessels, than of fibers.…”