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.Peer reviewe

Brown rot (BR) fungi are highly destructive wood decaying organisms that utilise free radicals in the initial stages of decay. Although many wood extractives have been shown to have antioxidant (AO) activity, their ability to protect wood from radical-based degradation has received little attention. The present paper reports on the ability of Scots pine heartwood (hW) and knotwood (knW) extractives to inhibit radical-based degradation, with a focus on the Fenton reaction. AO assays showed that extract solutions and pure pinosylvins had good radical scavenging activity and weak to moderate ferrous iron binding and ferric iron reducing activities. AO assays were repeated with wood powders and showed that extractives were also active in wood: hW and knW had significantly higher activities than their extracted counterparts or sapwood. However, when wood powders were subjected to degradation by Fenton reagent, only knW showed reduced mass loss. Based on the activity profiles of knW and hW, it appears that the radical scavenging activity of pine extractives is more important than their interaction with iron. The results suggest that the AO activity of extractives may play a role in inhibiting BR, but its importance relative to the other biological activities of extractives is unknown.