Biochemical evidence for the site of formation of gum arabic in Acacia senegal

Abstract

The anatomical site of gummosis in Acacia senegal was demonstrated by comparison of the carbohydrate analysis of the tissues from the inner bark, the cambial zone and the xylem of a gum-producing branch with the corresponding tissues of a branch which did not produce gum. The three anatomical zones were successively extracted for water-soluble polysaccharides and alkaline-extractable hemicelluloses. The material purified by hexadecyltrimethyl ammonium bromide precipitation was abundant in the aqueous extracts from the inner bark and the cambial zone of the gum producing branch, and was absent from the non-gummiferous branch. Neutral sugar and uronic acid analysis showed that the precipitated polysaccharides had the same composition as the gum produced by the same branch. The identity with gum arabic was further demonstrated by methylation analysis and 13C NMR spectroscopy. The same biochemical analyses showed that the presence of gum in the cambial zone was not restricted to the site of gum exudation but that gum existed on both sides of the scarification on the branch, even beyond the limits of the tapping.