Glandular Trichomes Morphology, Chemical Composition and Antimicrobial Activity of the Essential Oil of Three Endemic Scutellaria Taxa (Lamiaceae)

Abstract

The glandular trichomes morphology, volatile composition and antimicrobial activity of the aerial parts of three endemic Scutellaria taxa [S. cypria var. cypria Rechinger, S. cypria var. elatior Meikle and S. sipthorpii (Benth.) Hal.] from Lamiaceae were investigated. Examined species posses two morphologically distinct types of glandular trichomes. Capitate trichomes were observed in all three taxa. Peltate glandular trichomes had a large secretory head forming 1 central and 3-8 peripheral cells. Peltate trichomes were observed only in S. cypria var. elatior's petiole. The volatiles and the essential oil mixtures of three taxa were obtained by steam distillation in a Clevenger-type apparatus with a 0.26-0.47 % (v/w) yield. Their analyses were performed by GC-FID and GC-MS techniques. Identification of these compounds was exhibited by comparison of their mass spectra, relative retention indices and some literature records. In total, 23 components were identified. While, total volatile percentages were detected as 99.99 %, the essential oil yield ranged between 34.64 and 92.25 % for 3 species. Trans-caryophyllene (22.58 %) and germacren-D (42.01 %) were detected as major components for S. sibthorpii Eugenol (23.05 %) and palmitic acid (27.00 %) were the main components for S. cypria var. cypria Additionally, S. cypria var. elatior has a considerable amount of linalool and palmitic acid as 10.92 % and 46.76 %, respectively. The MIC values of the volatiles ranged as 10-20 mg/mL against Gram negative and Gram positive bacteria. C. albicans was found as the most resistant yeast-like fungus with a MIC values higher than 20 mg/mL.