Micromorphology and histochemistry of leaf trichomes of Salvia aegyptiaca (Lamiaceae)

Abstract

We performed a comprehensive study of trichomes considering the medicinal importance of the essential oils
produced in glandular trichomes of Salvia aegyptiaca L. and lack of data about leaf trichome characteristics. Micromorphological
and histochemical analyses of the trichomes of S. aegyptiaca were carried out using light and scanning electron
microscopy. We report that the leaves contained abundant non-glandular unbranched trichomes and two types of glandular
trichomes, peltate and capitate, on both leaf surfaces. The abaxial leaf side was covered with numerous peltate and capitate
trichomes, while capitate trichomes were more abundant on the adaxial leaf side, where peltate trichomes were rarely
observed. The non-glandular trichomes were unicellular papillae and multicellular, uniseriate, two-to-six-celled, erect or
slightly leaning toward the epidermis. Peltate trichomes were composed of a basal cell, a short cylindrical stalk cell and a
broad head of eight secretory cells arranged in a single circle. Capitate trichomes consisted of a one-celled glandular head,
subtended by a stalk of variable length, and classified into two types: capitate trichomes type I (or short-stalked glandular
trichomes) and capitate trichomes type II (or long-stalked glandular trichomes). Histochemical tests showed that the
secreted material in all types of S. aegyptiaca glandular trichomes was of a complex nature. Positive reactions to lipids
for both types of glandular trichomes were obtained, with especially abundant secretion observed in peltate and capitate
trichomes type II.