Abstract
Wood extractives are biologically active secondary metabolites that help protect wood and wood products from decay and other forms of biological attack. Despite the influence of distribution on their ability to protect wood, very few studies have investigated the distributions of extractives on a cellular level. In this paper, the distributions of extractives were studied in Scots pine (Pinus sylvestris L.) heartwood (HW) and knot heartwood by confocal Raman spectroscopy imaging. Pinosylvins, the antifungal phenolic extractives of pine, were found to be present in the cell walls, middle lamella, and lumina of tracheids. Their distribution suggested the existence of two different mechanisms of deposition and revealed similarities to the distribution of lignin. The potential binding of pinosylvins to lignin and their relatively low concentration in HW cell walls could explain why Scots pine HW is, on average, only moderately resistant to decay. Resin acids, the most abundant group of extractives in pine, were detected only within the lumina of tracheids and ray cells, where they may contribute to the reduced permeability of HW. The extractives distributions presented here help us understand the properties of HW and provide a deeper understanding of the origins of natural durability, which is of value in the current efforts to develop more environmentally friendly means of wood protection.
Highlights
Wood is a complex natural composite consisting primarily of cellulose, hemicelluloses, and lignin
The SW extract contained only minor amounts of resin acids, fatty acids or other monomeric extractives, suggesting that the extract consisted of mostly higher molecular weight material such as triglycerides, which are known to occur in significant quantities in sapwood (Piispanen and Saranpää, 2002; Willför et al, 2003)
Pinosylvin (PS) and pinosylvin monomethyl ether (PSM) were present in the HW samples, and the analysis indicated that in this case their concentrations were higher in middle heartwood (MHW) than OHW
Summary
Wood is a complex natural composite consisting primarily of cellulose, hemicelluloses, and lignin. In addition to these structural polymers, wood contains secondary metabolites called extractives, which occur primarily in the heartwood (HW) and knot heartwood (KHW) of trees. They are often low in abundance compared to the structural components, the extractives have a significant effect on the properties of wood, most notably its resistance to decay and other forms of biological attack (Hillis, 1987; Taylor et al, 2002). Pinosylvins and resin acids have both been linked to the decay resistance of pine HW (Harju et al, 2002; Venäläinen et al, 2004; Leinonen et al, 2008), and attempts have even been made to utilize these compounds as environmentally friendly wood protection agents (Celimene et al, 1999; Lu et al, 2016)
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