Histochemistry and micromorphological diversity of glandular trichomes in Melissa officinalis L. leaf epidermis

Due to the presence of glandular trichomes in their epidermis and production of essential oils, plants from the family Lamiaceae, including Melissa officinalis L., are commonly cultivated in most European countries and across Poland. With its diverse composition of essential oils and the wide range of pharmacological effects, the raw mate-rial of the lemon balm is widely applied in various branches of industry. In literature, there are no data presenting histochemical assays of glandular trichomes in the lemon balm; therefore, the aim of the study was to detect some substances with the use of select-ed stains and to characterise the micromorphology of the trichomes. The investigations were conducted using light, fluorescence, and scanning electron microscopes. The histochemical tests were based on Sudan Red 7b, Sudan black B, Nile blue, Nadi reagent, fer-ric chloride, potassium dichromate, magnesium acetate, Ruthenium red, and periodic acid-Schiff reagent. Digitiform as well as morphologically diverse capitate and peltate glandular trichomes were distinguished in the leaf epidermis. The histochemical tests showed heterogeneity of the composition of the lemon balm essential oil. They were applied to determine lipids, fatty acids, neutral fats, terpene compounds, polyphenols, flavonoids, and polysaccharide compounds in the analysed glandular trichomes. Improvement of the histochemical methods for analysis of glandular trichomes will expand the knowledge of the metabolism of secretory cells and facilitate future modification of their secretion products.