The structure and multiple functions of vessel-associated cells in xylem

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Vessel-associated cells (VAC) occur in the xylem of woody and herbaceous angiosperms and are in direct contact with a vessel wall via half-bordered pits. VAC can be ray or axial parenchyma cells and characterised by a high amount of mitochondria and ribosomes, a well-developed endoplasmic reticulum, few plastids, and various small vacuoles. These organelles indicate a high metabolic activity. Angiosperm vessels show considerable variation in the amount of VAC, although there is a continuum between vessel contact cells and distant cells. Interestingly, we find a positive correlation between vessel diameter and axial parenchyma fraction, which is also reflected in the amount of paratracheal axial parenchyma. This relationship is supported at the interspecific level and within growth rings of ring-porous species.
VACs show multiple functions, including: (1) storage of water, while starch is typically absent, with possibly functional consequences for hydraulic capacitance, embolism avoidance and/or refilling, and positive root/stem pressure, (2) xylem-phloem interactions via symplastic connectivity between parenchyma cells across ray initials in the vascular cambium, and (3) defence and resilience to frost, wound response, and pathogens. Several of these functions are likely affected by the unique, “protective” or “amorphous” layer that is most pronounced between the plasmalemma of the VAC and the parenchyma-vessel pit membrane. Unlike vessel-vessel pit membranes, the pit membrane and amorphous layer of VAC show pectic polysaccharides, which play a major role in the production of gels and tyloses in response to aging processes (heartwood formation), wounds, and infections.
Original languageEnglish
Title of host publicationAmerican Journal of Botany
Publication statusPrint publication - 4 Jul 2016
Externally publishedYes
EventBotanical Society of America - Annual botany conference, Savannah, Georgia - Georgia, Savannah , Sanannah, United States
Duration: 4 Jul 20168 Jul 2016


ConferenceBotanical Society of America - Annual botany conference, Savannah, Georgia
Country/TerritoryUnited States


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