The Study of Micromorphological and Essential oil Analysis of Nepeta binaloudensis and Nepeta cataria (Lamiaceae)

Abstract

Introduction The Nepeta is one of the largest genus of Nepetoide subfamily, in the Lamiaceae family with about 79 species in Iran. Most of the species are perennial rarely annual with different vegetative forms, leaves covered with trichome. Glandular trichomes are widely distributed all over the aerial part of Nepeta species, and their largely to its great importance and their structures can vary widely among plants species. Some species contain monoterpenes, sesquiterpenes, cyclopentanoid iridoids derivatives and nepetalactones which they are used in folk medicine as, diaphoretic, diuretic, antitussive, febrifuge agent. In the present work, scanning electron microscopy (SEM) was used to determine the nutlet micromorphology and also micromorphology and distribution of the glandular trichomes of Nepeta binaludensis “an Iranian endemic species” and Nepeta cataria in order to improve the knowledge of the species and to evaluate the usefulness of this feature for phytochemical and systematic purpose. The chemical composition of its essential oil was also analyzed. This paper provides a detailed description of trichome morphology and nutlet in Nepeta binaludensis andNepeta catariaspecies growing in Iran, by scanning electron microscopy (SEM), and evaluates the systematic significance of such characteristics.   Materials and Methods The research was conducted in research garden of Agricultural Faculty of Ferdowsi University of Mashhad during 2017. Seeds of two Nepeta species were provided by Institute of Plant Sciences in Ferdowsi University of Mashhad. The seeds were cultivation in greenhouse and the seedling (10 cm long) were transplanted in the field. During the summer aerial parts of the plants were harvested at flowering stage, dried in shade, and (30 g) were hydro distilled for 3 h using Clevenger apparatus. For SEM study, leaves were fixed with 3% glutaraldehyde in 0.1 M sodium phosphate buffer, pH 7.2 for 30 min at 4 °C. After washing in water the material was dehydrated through an ethanol gradient and critical point dried. Specimens were mounted onto SEM stubs using double-sided adhesive tape and coated with palladium. For nutlets observation, seed were directly mounted onto aluminum stubs using double-sided adhesive tape and coated with palladium and photographed.   Result Based on the obtained data, the surface leaves of both species (N. binaludensis and N.cataria) was observed forglandular and non-glandular trichomes distribution. (The glandular trichomes of the peltate types). Trichome density and size was variable as 7-21mm2 leaf surface (63-77 µm) in N. binaludensis and as 20-30 mm2 leaf surface (47-67 µm) in N.cataria. In both species only one types of glandular trichome was identified. Peltate trichomes comprise of a basal cell situated in the leaf epiderm with a four-celled secretory head. Nutlets of Nepeta were blackish-brown or brown in color. One type surface ornamentation, can be distinguished: smooth-type.  The nutlet ornamental pattern was smooth type with finely granulated in N. binaludensis and reticulate pattern in N.cataria species. Water-distilled essential oil of the aerial parts of two speciescultivated in field, were analyzed by GC and GC/MS. In essential oil of N.binaludensis and N. cataria, 51 and 26 components were identified, respectively. The main components of the essential oil of N. binaludensis were 1.8-cineole (14.8%), β-Pinene (10.4%) and p-Cymene (9.8%). Main compounds of the essential oil of N. cataria were 4a-a, 7-a, 7a-b-Nepetalactone (72/76%) and 4a-a, 7-a,7a-a-Nepetalactone (17.86%). Depending on the composition of key compound identified in essential oils, Nepeta species have been divided in two groups.   Conclusions  Depending on the composition of main compound identified in the essential oils, Nepeta species have been divided in two groups. On the basis of our research N. binaludensis belong to 1.8-cineole chemotype and of N.cataria belong to the nepetalactone chemotype. The leaves of N. binaludensis, N.cataria have be glandular and non-glandular trichomes. One types of glandular trichomes are identified: Peltate trichomes.Trichomes are distributed at the surface of leaves, having various functions and are extremely variable in the plants, plant organs location, density, form, therefore their morphology and structure could be of taxonomical importance in plant. Glandular trichomes contain or secrete substances which are widely used in pharmaceutical and cosmetic as well as in pesticide industry. The variation in the structure, morphology, density, secretion and function is noticed among these trichomes distributed on different plant organs. Nutlet surface can be useful as a taxonomic characteres.