Morphology, Anatomy and Ultrastructure of Reaction Wood

Whatever the species considered, trees reorient their axis by a very active mechanical action driven by variations of cambial activity. These variations of cambial activity will lead to variations in anatomy and ultrastructure of the xylem to achieve this biomechanical function, forming a type of wood called reaction wood, i.e. tension wood in angiosperms and compression wood in gymnosperms. This chapter focuses on the structure of reaction wood from the macroscopic level to the ultrastructural scale via the macro-, mesoand microscopic scales. It focuses in particular on differences between areas of reaction wood and other areas of wood around the circumference of the tree in terms of variation in appearance and structural organization. Therefore, the chapter starts with a description of the macroscopic appearance, followed by a description of the impact of reaction wood formation on the various tissues of the wood structure (vessels elements, fibres and parenchyma) leading to the variation occurring in the fibre cell wall and in the organization of the macromolecules inside the wall. Some methods or key features are described, for each scale, in order to highlight the occurrence of reaction wood. In addition, the limits of the described methods are discussed. Whatever the species considered, trees reorient their axis by a very active mechanical action driven by variations of cambial activity (Sinnott 1952). Those variations of cambial activity will lead to variations in anatomy and ultrastructure of the xylem to achieve this biomechanical function, forming a type of wood called reaction wood. As it was discussed in the previous chapter the term normal wood is often used to describe any wood that is not reaction wood. However, because J. Ruelle (*) INRA, UMR 1092, Laboratoire d’Etude des Ressources Forêt-Bois (LERFoB), Centre INRA de Nancy-Lorraine, 54280 Champenoux, France e-mail: [email protected] B. Gardiner et al. (eds.), The Biology of Reaction Wood, Springer Series in Wood Science, DOI 10.1007/978-3-642-10814-3_2,© Springer-Verlag Berlin Heidelberg 2014 13 wood from the opposite side of reaction wood can also show some variations in terms of anatomy or properties we decided to name the wood from the lateral and opposite zones relative to any reaction wood using the term “non-reaction wood” wherever possible. During this chapter we will focus on each different scale of reaction wood one by one, especially on the differences between the reaction wood sector and other sectors around the circumference of the tree. One very important point to remember is that the process of axis reorientation in trees is always based on circumferential heterogeneity in cambial region activity occurring at various distinct structural