Peripheral defence strategy: variation of barbaloin content in the succulent leaf parts of Aloe arborescens Miller (Liliaceae)

Aloe arborescens is a large, multi-stemmed shrub and is one of the very com mon Aloe species along the Indian Ocean coast of southern Africa, from the Cape, in the south, to Zimbabwe and Malawi in the north. It is used as a he dge plant to protect agricultural fields or stock and as a horticultural pl ant in gardens. Barbaloin, a secondary phenolic metabolite, is distributed in the plants as part of a peripheral defence strategy. Barbaloin content w as found to be highest in the youngest leaves. Within these, concentration varied: at its highest in the terminal third of the leaf, at its lowest in the basal third; higher in the terminal, adaxial, leaf margin and lower in the basal, abaxial, leaf centre. The more times a leaf is cut, the higher t he barbaloin content of the new growth from the leaf base that remains on t he plant. This may deter animals such as elephants and kudu from eating the new growths. They may prefer to eat other plants that have not been damage d by consumption for longer periods. This phenomenon may give damaged plant s the chance to renew themselves before their leaves are consumed again. (C ) 2000 The Linnean Society of London.