Structural and histochemical investigation of the glandular trichomes of Salvia aurea L. leaves, and chemical analysis of the essential oil

Abstract

Anatomical and histological investigations of the secretory hairs of Salvia aurea leaves, and identification of the main components of the essential oil were carried out. Two types of glandular trichome were found: peltate glands, characterized by a short stalk and a large six to eight-celled head, and capitate trichomes which were further subdivided into two kinds, the first with a short monocellular stalk and two-cellular head (type I), and the second with a multicellular stalk, a neck cell and a small globose unicellular head (type II). Whereas peltate glands and type I capitate trichomes were always present, type II capitate glands were not found in all leaf samples. The histochemical study suggested an 'endodermal' role for the stalk cell (peltate and capitate type I) as well as for the neck cell (capitate type II), preventing the loss of essential oil. Histological reactions also revealed the complex nature of the material secreted by all types of S. aurea trichome, including polysaccharides, polyphenols and proteins, in addition to the essential oil. Qualitative and quantitative GC-MS analysis of the essential oil revealed camphor to be the main constituent. The findings are discussed in relation to studies of trichomes from other members of the Lamiaceae.