Morphology and histochemistry of the glandular trichomes of Lippia scaberrima (Verbenaceae).

BACKGROUND AND AIMS: Lippia scaberrima, an aromatic indigenous South African plant, with medicinal application, potentially has economic value. The production of essential oil from this plant has not been optimized, and this study of the chemico-morphological characteristics was aimed at determining the location of oil production within the plant. Furthermore, the locality of other secondary metabolites important in medicinal applications needed to be ascertained. This information would be useful in deciding the protocol required for isolation of such compounds. METHODS: The morphology of the glandular trichomes was investigated using a combination of scanning electron and light microscopy. Concurrently, the chemical content was studied by applying various chemical reagents and fluorescence microscopy. KEY RESULTS: Three types of trichomes were distinguished on the material investigated. Large, bulbous peltate glands containing compounds of terpenoid nature are probably the main site of essential oil accumulation. Small glands were found to be both peltate and capitate and fluorescent stain indicated the possible presence of phenolic compounds. The third type was a slender tapered seta with an ornamented surface and uniseriate base, and evidently secretory in nature. CONCLUSIONS: This study linking the chemical content and morphology of the glandular trichomes of L. scaberrima has contributed to the knowledge and understanding of secretory structures of Lippia spp. in general.

An appropriate method for extracting the insect repellent citronellol from an indigenous plant (Pelargonium graveolens L'Her) for potential use by resource-limited animal owners.

Veterinary needs appraisals in rural, peri-urban and urban areas have indicated a need for affordable and accessible veterinary health care. It was also found that farmers and animal owners used indigenous plants for treating animals. In Africa, insects such as Culex, Culicoides and Stomoxys may transmit diseases, cause irritation to animals or prevent wound healing. Insect repellents used topically are generally safer and cheaper than insecticides. Using readily available commercial sources of ethanol 43% v/v (brandy and cane spirits), it was shown that citronellol could be extracted from uncrushed leaves of the indigenous shrub Pelargonium graveolens L'Hér. Efficacy of extraction was compared to that using reagent grade absolute ethanol. The peak concentration of citronellol was achieved within 7 days of extraction and thereafter remained constant for 4 months. Extraction methods using tap water and cooking oil were not successful. The extraction was also less successful when the leaves were crushed or macerated before being placed into ethanol. Gas chromatography was used to monitor the concentration of citronellol in the different extracts.