Atlas of plant and animal histology

Resin ducts are internal secretory structures composed of cells derived from the vascular cambium. They start as clusters of cells that differentiate and create hollow spaces mostly by schizogeny. They are typical of conifers, appearing in roots, stems, leaves, and cones. Resin ducts are found among the parenchyma cells of leaves and stems, in the primary xylem of stems and roots, as well as intermingled with the cells of the secondary xylem of stems. In the xylem and cortex of stems, there are axial resin ducts, that is, they run parallel to the long axis of the stem. The stem cortical resin ducts are major reservoirs during the early years of development. However, the larger resin ducts are observed in the late xylem. There are also axial resin ducts that connect adjoining radial ducts.

They are long, tube-like structures containing epithelial cells that release a resinous exudate into the lumen. These tubes are typically 20 mm long and 150 µm wide. The lumen is lined with a secretory epithelium that can be uniseriate, as in the xylem, or biseriate, like in the cortical parenchyma (see images below). In pines, the epithelial cells are generally thin-walled and remain active for several years. Resin canals can be formed in response to infections or pathogens, meaning there are constitutive and induced resin ducts. The induction may be either local or systemic (affecting the entire plant).

The resin is produced, stored, and conducted within secretory structures forming a complex network of interconnected ducts. The resin is a mixture of substances composed mainly of terpenes. The toxic resinous compounds protect the plant from a wide range of herbivores, insects (such as the beetles), and pathogens (such as fungi), while the volatile phenolic compounds may attract benefactors such as parasites or predators of the herbivores that attack the plant. The resin acts as a physical and chemical barrier that prevents pathogen entry by filling the wounds.In addition, following exposure to the air, the resin crystallizes to form a plug. The amount of released resin depends on the diameter of the wound and the density of resin ducts of the tree. This has been related to the resistance of species to pathogens. However, there is a nematode species that can infect some resiniferous trees by moving through the resiniferous ducts.

• Bibliography ↷

  • Vázquez-González C, Zas R, Erbilgin N, Ferrenberg S, Rozas V, Sampedro S. (2020). Resin ducts as resistance traits in conifers: linking dendrochronology and resin-based defences. Three physiology. 40: 1313-1326. DOI: 10.1093/treephys/tpaa064.

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