Juvenile and Compression Wood Cell Wall Layers Differ in Lignin Structure in Norway Spruce and Scots Pine

Dibenzodioxocin, an 8-ring substructure of lignin identified in the mid- 1990's, is known to occur in softwood cell walls especially in the S3-layers of normal wood. In this study the lignin substructure was immunolocalised in juvenile and mature wood as well as in different degrees of compression wood of Norway spruce ( Picea abies (L.) H. Karst.) and Scots pine ( Pinus sylvestris L.). In juvenile wood of Norway spruce, dibenzodioxocin was hardly present in the tracheid cell wall, while in Scots pine some dibenzodioxocin was found evenly distributed in the S 2 -layers. In mature normal wood, dibenzodioxocin was localised in the S 3 -layers in both Scots pine and Norway spruce. In contrast, in compression wood tracheids of Scots pine, where the S 3 -layer is not present, dibenzodioxocin was found in the S 1 -layers and in the outer part of the S 2 -layers, while in Norway spruce the innermost cell wall layer showed a strong signal. These findings support the idea that in mature wood the condensed dibenzodioxocin structure is formed in Norway spruce at the end of lignification, when the supply of monolignols and probably also hydrogen peroxide is diminishing. The reasons for Scots pine juvenile and compression wood showing a different pattern of dibenzodioxocin labelling is discussed.