Taxonomic patterns in the distribution of polyols within the Proteaceae

Abstract

More than 120 leaf samples from 82 species of Proteaceae, representative of floras in South Africa, Australia, New Zealand and South America, were studied for sugar composition. Generally, sucrose was dominant, with one or another polyol being second in importance. Presence of polygalatol (1,5-anhydrosorbitol), bornesitol (O-methyl-myo-inositol) and quebrachitol (O-methyl-D-chiro-inositol) was confirmed, pinitol (O-methyl-L-chiro-inositol) was identified and high levels of myo-inositol were sometimes encountered. Only four species, including Placospermum lacked any polyol other than inositol. High concentrations of polygalatol were characteristic of two South African genera, Protea and Faurea. Pinitol was characteristic of three genera in the Persoonieae and was also found in Petrophile (Australian) and Aulax (African). Most other genera were characterised by bornesitol alone, or by quebrachitol plus smaller amounts of bornesitol and inositol. Other unidentified compounds in the sugar fraction (possibly inositol isomers and glycosides) have potential to provide additional information on relationships. With only two exceptions, the pattern was consistent within a genus as currently defined; however, there was only partial concordance between the polyols and the phylogenetic relationships of genera. The findings support relatively close affinity between Buckinghamia and Grevillea, and between Aulax and Petrophile, as concluded from DNA sequencing. We suggest that the ability to produce the various inositol-based polyols in Proteaceae evolved early in the evolution of this ancient family, and has been retained in a wide range of habitats. Polygalatol has to be synthesised through a different biochemical pathway, which appears to have evolved later.