Ultrastructural and histochemical analysis of glandular trichomes of Marrubium vulgare L. (Lamiaceae)

- Micromorphological and anatomical investigation of white horehound trichomes.
- The presence of various secondary metabolites determined by histochemical tests.
- The ultrastructure of the bicellular head of the capitate trichome.

Anatomical and ultrastructural investigations of the glandular trichomes of aboveground organs of the white horehound (Marrubium vulgare L.) were carried out. Additionally, identification of the main components of the secreted products was conducted. The following types of glandular structures were found: peltate with a stalk cell and a large eight-celled head and capitate trichomes, which were divided into three types: I. long-stalked with a 1-celled head, II. short-stalked with a 2-celled head, III. short-stalked capitate with a 4-celled head. Histochemical tests showed that the glands contained various substances such as lipids, polysaccharides, phenolic compounds, terpenes, tannins, and flavonoids. During the secretory stage, the ultrastructure of the bicellular head of the capitate trichome was characterized by a highly developed rough endoplasmic reticulum, numerous plastids, and mitochondria. After exocytosis, the secretion was temporarily stored in the periplasmic space and passed through the cell wall to the subcuticular space.

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