Seasonal dynamics of cell-to-cell transport in angiosperm wood.

This study describes the seasonal changes in cell-to-cell transport in three selected angiosperm tree species, Acer pseudoplatanus (maple), Fraxinus excelsior (ash), and Populus tremula × tremuloides (poplar), with an emphasis on the living wood component, xylem parenchyma cells (XPC). We performed anatomical studies, dye loading through the vascular system, non-structural carbohydrate (NSC) content measurements, immunocytochemistry, inhibitory assays and qRT-PCR to analyze the transport mechanisms and seasonal variations in wood. The abundance of membrane dye in wood varies seasonally along with seasonally changing tree phenology, cambial activity, and NSC levels. Moreover, dyes internalized into vessel-associated cells (VAC) and "trapped" in the endomembrane system are transported farther between other XPC via plasmodesmata. Finally, various transport mechanisms based on clathrin-mediated and clathrin-independent endocytosis, and membrane transporters operate in wood, and their involvement is species- and/or season-dependent. Our study highlights the importance of XPC in seasonally changing cell-to-cell transport in both ring-porous (ash) and diffuse-porous (maple, poplar) tree species and demonstrates the involvement of both endocytosis and plasmodesmata in intercellular communication in angiosperm wood.