Chemical Composition, Leaf Trichome Types and Biological Activities of the Essential Oils of Four Related Salvia Species Indigenous to Southern Africa

The essential oils from fresh aerial parts of four Salvia species indigenous to southern Africa were obtained by hydrodistillation and analyzed by GC and GC/MS. Quantitative rather than qualitative differences in oil composition were observed. Forty-three compounds in each species accounting for 78% (S. africana-caerulea), 78% (S. africanalutea), 96% (S. chamelaeagnea) and 81% (S. lanceolata) of the total composition were identified. Salvia africana-caerulea and S. lanceolata were dominated by oxygen-containing sesquiterpenes (59% and 48%, respectively). Oxygen-containing monoterpenes dominated in S. chamelaeagnea (43%), while monoterpene hydrocarbons (36%) were abundant in S. africana-lutea. Scanning electron and light microscopy of the indumentum of the leaves revealed the presence of glandular and non-glandular trichomes. Non-glandular point-shaped trichomes composed of two or three cells are common in all four species and two types of glandular trichomes were noted: peltate trichomes, with up to 16 head cells and a capitate type varying in the number of cells comprising the head and stalk. The oils were evaluated against two Gram-positive and two Gram-negative bacterial strains using the microdilution method and the MIC values ranged from 0.8 to 32 mg/mL. The oils exhibited antiplasmodial (5 < IC50 < 9 μg/mL) and anti-inflammatory (43 < IC50 < 77 μg/mL) activity as determined by the [3H]-hypoxanthine radiometric and 5-lipoxygenase methods, respectively. Compared to other naturally derived antiplasmodial compounds (e.g. quinine) the oils are more toxic to human kidney epithelium cells (MTT method) with the IC50 values ranging from 2-7 μg/mL. The oils exhibited poor antioxidant activity against the DPPH radical at 100 μg/mL.