The distribution of the phenolic metabolites barbaloin, aloeresin and aloenin as a peripheral defense strategy in the succulent leaf parts of Aloe arborescens

Aloe arborescens is a large, multi-stemmed shrub. It is used as hedge plant s to protect agricultural fields or stock and as horticultural plants in ga rdens. In natural habitats it 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. Secondary phenolic metabolites such as ba rbaloin (Rf 0.31-0.35), aloeresin (Rf 0.25-0.3) and aloenin (Rf 0.51-0.55) have been found to be distributed in the succulent leaves of Aloe auboresce ns in a peripheral defense strategy. The youngest leaves have the highest c ontent. The terminal third of each leaf has the highest content and the bas al third, the lowest. Along the leaf margins, on the top third and adaxial side, the content is the highest and in the base third, the lowest along th e leaf center on the abaxial side. Similar relative amounts of these three secondary phenolic metabolites were found in the different leaf locations. The leaf orientation may affect the total content of these three phenols bu t not their relative amounts in the different parts of the leaves. It is po ssible that the more often the plant parts are damaged by consumption by an imals such as elephants, kudu or insects, the greater the increase of their phenolic metabolites. This increase may reduce or prevent further consumpt ion when the content of the metabolites reaches a certain level. The plants then have a chance to renew themselves. (C) 2000 Elsevier Science Ltd. All rights reserved.