Within-tree variability and sample storage effects of bordered pit membranes in xylem of Acer pseudoplatanus

Intervessel pit membranes have been suggested to account for more than half of the total xylem hydraulic resistance in plants and play a major role in vulnerability to drought-induced hydraulic failure. While the thickness of intervessel pit membranes was found to be associated with xylem embolism resistance at an interspecific level, variation in pit membrane structure across different organs along the flow path within a single tree remains largely unknown. Based on transmission electron microscopy, we examined intra-tree variation of bordered pit and pit membrane characteristics in xylem of roots, stems, branches, petioles, and leaf veins of Acer pseudoplatanus. Moreover, potential preparation artefacts on pit membrane structure such as alcohol treatment and dehydration were tested. Our observations showed quantitative differences in bordered pits across organs, including variation in pit membrane thickness within and across organs. Vessel size was weakly related to intervessel wall thickness, but not significantly linked to pit membrane thickness. Gradual dehydration of wood samples resulted in irreversible shrinkage of pit membranes, together with increased levels of aspiration. These findings are relevant to explore similarity in xylem embolism resistance across plant organs.