Ultrastructure and histochemistry of secretory ducts in Artemisia campestris ssp. maritima (Compositae)

The histochemical characterization of the oleoresin produced by secretory ducts of Artemkiu campestris ssp. maritima revealed the presence of terpenoids (essential oils, resiniferous acids and probably steroids), alkaloids and fatty acids, eventually polyacetylenes. The ultrastructural study of A. campestris ducts enabled us to consider that the secretory activity begins very early during the duct development. The oleoresin deposited in the duct cavity is produced by epithelial and sub‐epithelial cells that contain, at the secretory phase, a great amount of smooth endoplasmic reticulum (SER) surrounding plastids with few thylakoids. These organelles may play an important role in the oleoresin production, the SER probably being responsible for some steps in the biosynthesis of oleoresin components and for the transport of the secreted material towards the plasmalemma. Endoplasmic reticulum and mitochondria probably have a role in the synthesis of steroids. After secretion, the duct glandular cells degenerate progressively. The extrusion process of secretion may be considered mero‐holocrine.