No abstract

The distribution of the secondary phenolic compound, barbaloin, in Aloe arborescens leaves depends on the leaf part, age, and position of the leaf, as well as on seasonal influences. Young and old leaves of A. arborescens were cut from plants monthly and the exudate was immediately freeze-dried. The barbaloin levels were determined spectrophotometrically at λmax, 360–362 nm after separation by TLC. In all leaves the tissue of the basal third of the leaf had the lowest barbaloin content, the upper third contained the highest percentage, and the middle part contained the intermediate percentage. After cutting young leaves, the new basal part that grows after replanting has a higher barbaloin content after about five months when compared with the same part before cutting. In the 16 leaves of a cutting rooted two years before the experiment, the highest barbaloin content was found in the four upper young leaves (63%). In all the other leaves the barbaloin content was found to be only between 13 and 22%. There are also seasonal influences on the barbaloin content of young leaves. When old and young leaves were compared, the higher barbaloin content was found in the young leaves harvested at the same time.

No abstract

Eight leaves from four different plants of Aloe hereroensis and 18 leaf parts of each leaf were tested by anatomic, fluorescence microscopy and TLC methods. Four phenolic secondary metabolites, homonataloin and three isomers of aloeresin, were found in the leaves. The highest content of these metabolites was found in the top third of a leaf and along the leaf margins. In the margins, the content of the four secondary metabolites in the adaxial was higher than in the abaxial direction. In the centre parts of the leaves, the metabolic content of the abaxial parts was higher than in the adaxial parts. The results indicate that homonataloin mainly accumulates in the inner bundle sheath cells (IBSC). The three isomers of aloeresin appear in the outer bundle sheath and in the boundary cells between the chlorenchyma and water‐storage tissues. The density of the vascular bundles, the area ratio of the chlorenchyma to the tested counterpart, and the area ratio of the IBSC to a whole bundle are important structural factors to determine the differences in the content of these four secondary metabolites in all the leaf parts. The distribution according to the rosette leaf arrangement and the existence of the ‘cocktail’ of four phenolic secondary metabolites indicate a peripheral defence strategy of this plant. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 138, 107–116.

No abstract