Structural studies of acidic xylans exuded from leaves of the monocotyledonous plants Phormium tenax and Phormium cookianum

The polysaccharides exuded from both Phormium tenax and Phormium cookianum leaves are acidic xylans with molecular weights in the range 1.3×106–1.7×106 Da. 1H and 13C NMR spectra show that in both cases the backbone comprises 1,4-linked β-d-Xylp units and their substituted products, including a structural unit that is both 2-O-substituted and 3-O-acetylated. The sidechains contain α-d-GlcA and are terminated by β-d-Xylp and α-l-Araf units in relative proportions that differ between plant varieties. The polysaccharides are so highly branched that chain-terminating units account for approximately half of all structural units. These properties place the Phormium polysaccharides in a class which includes brea, sapote and yabo gums.