Submitted to: International Journal of Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/2/2007
Publication Date: 5/5/2008
Citation: Favi, F., Cantrell, C.L., Mebrahtu, T., Kraemer, M.E. 2008. Leaf Peltate Glandular Trichomes of Vernonia galamensis ssp. galamensis var. ethiopica Gilbert: Development, Ultrastructure and Chemical Composition. International Journal of Plant Science. 169(5):605-614. Interpretive Summary: The genus Vernonia (Asteraceae) contains more than 500 species distributed in Africa and the Americas, most of which have bitter tasting leaves. V. galamensis spp. galamensis var. ethiopica Gilbert (VGAE), an herbaceous plant from Eritrea in northeast Africa, is currently being studyied as a potential new oilseed crop. The seed is rich in vernolic acid, a unique epoxy oil characterized by unusually low viscosity and thus valuable in paints, plasticizers, and flexible resins. Leaves from plants in the Vernonia genus contain flavonoids, sesquiterpene lactones and other biologically active compounds that have been used for centuries in traditional African medicine and even by chimpanzees to cure ailments. They have also been used by Africans to control and repel insects. Leaf extracts from Vernonia have shown potential for drug and pesticide development but nothing has been published on the ultra-structure and chemical composition of the glandular trichomes believed to be responsible for the production of these compounds. This study is a contribution toward the understanding of trichome structure, development and glandular content. Herein we report the development and chemical content of the peltate biseriate glandular trichome.
Technical Abstract: Plants from the genus Vernonia produce a variety of flavonoids and bitter sesquiterpene lactones important for agriculture and human health. Leaf glandular trichomes of Vernonia galamensis ssp. galamensis var. ethiopica Gilbert (VGAE) were investigated for ultrastructural development and content composition because sesquiterpene lactones that impart a bitter taste to the leaves have been associated with the presence of these glands. Trichome ultrastructure was examined using light microscopy, and scanning and transmission electron microscopy. Glands were removed from the leaf surface and chemical composition of gland contents was determined using high performance liquid chromatography (HPLC) and high-resolution mass spectrometry techniques. Immature and mature ten-celled peltate biseriate glandular trichomes were observed only at the abaxial side of the leaf. Then, a large subcuticular space (head) developed from the topmost cells pair of the mature trichome and gradually filled with a substance that appeared dark brown under phase contrast microscope. HPLC mass spectrometry analysis revealed that the major constituent of the gland was prevernocistifolide-8-O-isobutyrate. This glaucolide-type sesquiterpene lactone was previously identified as a major constituent of the aerial parts of VGAE.