Hakaru Inaoka

Extracellular polysaccharides produced by tuberose callus

A high yield of extracellular polysaccharide (ECP) was obtained from callus cultures of tuberose (Polianthes tuberosa), which could be separated into an unadsorbed and two acidic fractions (TPS-1, -2) by ion-exchange column chromatography. The yields of each fraction were markedly increased by the addition of 10(-5) M 2,4-dichlorophenoxyacetic acid to the medium. Of the three fractions, the amount of TPS-1 accounted for over 60% of total yield of ECP, which was a predominant polysaccharide consisting of arabinose (Ara), mannose (Man) and galactose (Gal) as major neutral monosaccharides. Judging from the patterns of electrophoresis and ultra-centrifugation, TPS-1 was identified to be homogeneous. Methylation and GC-mass spectrometry analyses of this fraction revealed the presence of 1,2,3-linked Man, 1-linked Ara, 1,3-linked Ara, 1-linked Gal and 1,3,4-linked glucuronosyl (GlcUA) residues in a molar ratio of 1.0:1.08:0.85:0.75:1.08. Based on additional analyses of the mild acid hydrolysate and the absolute configuration of the constituent monosaccharides, a possible structure for TPS-1 was a glucuronomannan possessing the unit of -->4)-beta-D-GlcUAp-(1-->2)-alpha-D-Manp-(1--> with branching at the C-3 position, where -->1)-alpha-L-Araf, -->1)-beta-D-galp, -->1)-alpha-L-Araf-(3-->1)-alpha-L-Araf or -->1)-alpha-L-Araf-(3-->1)-beta-D-Galp were attached randomly. About 35% of the GlcUA moieties were present as methyl esters. Further confirmation was made by 1H and 13C NMR spectroscopy.