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Comparison of Micropore Distribution in Cell Walls of Softwood and Hardwood Xylem.

Research paper by Lloyd A LA Donaldson, Mathew M Cairns, Stefan S Hill

Indexed on: 16 Sep '18Published on: 16 Sep '18Published in: Plant physiology



Abstract

The porosity of wood cell walls is of interest for both understanding xylem functionality and from a wood materials perspective. The movement of water in xylem generally occurs through the macroporous networks formed in softwood by bordered pits and in hardwood by the intervessel pits and open conduits created by vessels and perforation plates. In some situations, such as cavitated xylem, water can only move through the micropores that occur in lignified tracheid and fiber cell walls; however, these micropore networks are poorly understood. Here, we used molecular microscopy analysis of radiata pine (Pinus radiata D. Don) and red beech (Nothofagus fusca Hook.f.) to determine the distribution of micropores in the secondary walls and middle lamellae of tracheids and fibres in relation to cell wall composition. Using two different types of probe, we identified a greater porosity of secondary cell walls and a reduced porosity of the middle lamella. Areas of reduced porosity were observed in the outer regions of the secondary cell wall of both tracheids and fibres that appear unrelated to lignification or the distribution of cellulose, mannan, and xylan. Hardwood fibre cell walls were less lignified than those of softwood tracheids and showed greater accessibility to porosity probes. Vessel cell walls were comparable to those of fibres in terms of both porosity and lignification. Lignification is probably the primary determinant of cell wall porosity in xylem. The highly lignified middle lamella, and lumen surface, act as a barrier to probe movement and therefore water movement in both softwood and hardwood. {copyright, serif} 2018 American Society of Plant Biologists. All rights reserved.