Influences of leaf pruning on the content of the secondary phenolic metabolites barbaloin, aloeresin and aloenin, in the leaves of Aloe arborescens

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. Figure 10. The ratio of the volume of the chlorenchyma to the whole tested leaf counterparts (% ± SE) of 12 leaf parts of Aloe hereroensis leaves (Fig. 5), as well as the width of the chlorenchyma (mm ± SE)

Chemosystematic evaluation of Aloe section Pictae (Asphodelaceae)

“…The genus has been the subject of considerable phytochemical research during the past century, intended to characterise and authenticate natural products from species in trade and identify their bioactive properties. The purgative effects of Aloe leaf exudate ('drug aloes') have been attributed to anthraquinone C-glycosides, notably barbaloin and aloins A and B (Reynolds, 1985;Chauser-Volfson and Gutterman, 2004;Steenkamp and Stewart, 2007). The mucilaginous leaf mesophyll ('aloe gel') is rich in acylated polysaccharides possessing anti-inflammatory properties (Steenkamp and Stewart, 2007).…”