Glandular trichomes of Rosmarinus officinalis L.: Anatomical and phytochemical analyses of leaf volatiles

Abstract

Rosmarinus officinalis is known for the production of volatile compounds used in medicinal and food preparations. Leaves of R. officinalis are densely covered with capitate and peltate glandular trichomes where biosynthesis of volatiles mainly occurs. This study aims to conduct a morphological assessment to identify anatomical characteristics of both leaves and trichomes, as well as a chemical analysis of leaf volatile compounds, using histochemistry and stem distillation extraction. Specifically, anatomical and chemical constituents of the secretory structures of R. officinalis leaves were investigated using light and scanning electron microscopy, in addition to gas chromatography. One peltate and three types of capitate glandular trichomes were observed on the leaves of R. officinalis. Histochemical tests showed positive reactions to lipophilic compounds for both capitate and peltate trichomes, with only a slight detection of terpenoids with carbonyl group in peltate glands. Gas chromatography revealed camphor (23.2%) as the main volatile compound, mostly accumulating in peltate glandular trichomes. This phytochemical study of volatile compounds, together with anatomical and histochemical analyses of R. officinalis leaves, demonstrated the importance of leaves as a center of volatile production in peltate and capitate trichomes, as well as the nature of volatile composition, which is involved in species survival.

Keywords:

• Glandular trichomes
• histochemistry
• leaf anatomy
• terpenoids
• volatile organic compounds

Acknowledgments

We thank CAPES/Brazil-Cuba for providing a fellowship to the first author, Mr. Elivaldo Lima (Museu Nacional/UFRJ) for assistance with scanning electron microscopy, Jefferson Ferrão for help with the figures, and Siannah M. Más Diego, MSc., (CNEA/UO) for revision of the English text.