Content and distribution of anthrone C-glycosides in the South African arid plant species Alloe mutabilis growing in direct sunlight and in shade in the Negev Desert of Israel

The content of the secondary metabolites anthrone C-glycosides (barbaloin, homonataloin and nataloin) in Aloe mutabilis leaves are the highest in the upper third of each leaf. The content of these phenolic metabolites is also higher in young leaves than in older leaves, and higher in plants grown in shade than in direct sunlight. There are also significant monthly differences in the content of these metabolites, which are more pronounced in young leaves than in old leaves. We hypothesize that the higher content of these compounds in the periphery of the leaves and plants is a defense strategy against leaf-eaters.