Copper nanoparticles can penetrate the cell walls of unlignified parenchyma cells in southern pine wood treated with a micronised wood preservative, but they are excluded from lignified tracheid walls. This paper extends these observations to include the cell wall layers of the bordered pit. Focused ion beam and ion milling were used to make an ultra-thin section of the cell wall layers of an earlywood bordered pit excised from southern pine wood that had been treated with a micronised wood preservative. High resolution transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy in combination with energy dispersive analysis of X-rays were used to detect and examine the penetration of the torus and pit border by copper. Copper was more abundant in the torus than in the pit border, but the depth of penetration of copper in both cell wall layers was approximately the same, ~100nm. High resolution transmission electron microscopy was unable to detect crystalline material in either the torus or pit border. Therefore we conclude that copper nanoparticles are unable to penetrate the torus and border of the bordered pit in accord with our previous observation that nanoparticles are excluded from the cell walls of lignified tracheids.

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