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

A h arbmcm is a large, multi-stemmed shrub and is one of the very common 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 hedge plant to protect agricultural fields or stock and as a horticultural plant in gardens. Barbaloin, a secondary phenolic metabolite, is distributed in the plants as part of a peripheral defence strategy. Barbaloin content was 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 the barbaloin content of the new growth from the leaf base that remains on the 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 damaged by consumption for longer periods. This phenomenon may give damaged plants the chance to renew themselves before their leaves are consumed again.