The molecular architecture distinctions between compression, opposite and normal wood of Pinus radiata

Rosalie Cresswell¹Alan Dickson²Michael Robertson²Suzanne Gallagher²Regis Risani²Marie-Joo Le Guen²Henry Temple³Aleksandra Liszka^4,5Lloyd Alister Donaldson²Nigel Kirby⁶John Ralph⁷Jan Lyczakowski⁴Stefan James Hill²Paul Dupree^8*Ray Dupree^1*Mathias Sorieul^2*

• ¹University of Warwick, Coventry, West Midlands, United Kingdom
• ²New Zealand Forest Research Institute Limited (Scion), Christchurch, Canterbury, New Zealand
• ³Sainsbury Laboratory, School of Biological Sciences, University of Cambridge, Cambridge, England, United Kingdom
• ⁴Department of Plant Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Kraków, Lesser Poland, Poland
• ⁵Doctoral School of Exact and Natural Sciences, University of Białystok, Białystok, Podlaskie, Poland
• ⁶Australian Synchrotron, Clayton, Australia
• ⁷Wisconsin Energy Institute, University of Wisconsin-Madison, Madison, Wisconsin, United States
• ⁸Department of Biochemistry, University of Cambridge, Cambridge, England, United Kingdom

In gymnosperms compression wood is a specialised type of structural cell wall formed in response to biomechanical stresses. The differences in terms of gross structure, ultrastructure and chemistry are well-known. However, the differences between compression wood, normal wood, and opposite wood regarding the arrangements and interactions of the various polymers and water within their cell walls still needs to be established. The analysis of 13 Clabelled Pinus radiata by solid-state NMR spectroscopy and other complementary techniques revealed several new aspects of compression and opposite wood molecular architecture. Compared to normal wood, compression wood has a lower water content, its overall nanoporosity is reduced, and the water and matrix polymers have a lower molecular mobility. Galactan, which is a specific marker of compression wood, is broadly distributed within the cell wall, disordered, and not aligned with cellulose, and is found to be in close proximity to xylan. Dehydroabietic acid (a resin acid) is immobilised and close to the H-lignin only in compression wood. Although the overall molecular mobility of normal wood and opposite wood are similar, opposite wood has different arabinose conformations, a large increase in the amount of chain ends, contains significantly more galactan and has additional unassigned mobile components highlighting the different molecular arrangement of cell wall polymers in opposite and normal wood.