Polysaccharide from the Gum Exudate from Vochysia tucanorum: Comparison with Other Vochysia spp.
Wagner, R.1; Pereira, G.C.Z.1; Simas, F.F.1; Angeli, A.2; Brito, J.O.2; Silva, M.A.3; Sassaki, G.L.1; Iacomini, M.1; Gorin, P.A.J.1
1Departamento de Bioquímica, Universidade Federal do Paraná, Curitiba, PR, 81531-990, Brazil; 2Departamento de Ciências Florestais, ESALQ, Piracicaba, SP, Brazil; 3RECOR, Reserva Ecológica do IBGE, Brasília, DF
Vochysiaceae is a largely neotropical family of trees growing in the rain forest and savannah of South America. Vochysia lehmannii produced a gum exudates on its trunk containing a heteropolysaccharide with a main chain of repeating b-GlcpA-(1®2)-a-Manp-(1®4)-b-GlcpA-(1®2)-a-Manp- repeating groups and with highly complex side-chains with Ara units. We now compare its structure with the exudate polysaccharides mainly with V. tucanorum and partially with V. thyrsoidea. The former was collected in the Floresta Estadual de Assis, SP and the latter in the Reserva Ecológica do IBGE, Brasília, DF (RECOR). The gum of V. tucanorum was successively extracted with water at 25ºC, 100ºC and 1M KOH at 25ºC. Ethanolic precipitates of all extracts were fractions PVT, PVTQ and PVTK respectively, HPSEC analysis of each showed their heterogeneity. Each fraction was submitted to a freeze-thawing process, which gave rise to a soluble fraction and a precipitate, each one being homogeneous. All fractions contained Ara, Gal and uronic acid as major components, Man, Glc, and Xyl in minor proportions. The 13C-NMR spectra of each of the 6 fractions were very similar and had complex C-1 regions from a-Araf and b-Galp units. Methylation analysis and controlled Smith degradations showed the presence of an acidic arabinogalactan with a (1®3)-linked b-Galp main chain and high proportion of side chains of GlcA and Ara units (including nonreducing end-units). The EtOH supernatant contained a (1®4)-linked b-xylan (methylation analysis, and 1D and 2D NMR). A polysaccharide with similar monosaccharide units was present in the gum of V. thyrsoidea. This was surprising since the main chain of V. lehmannii had a different structure. Generally, there is a consistency of structure within the same genus, but not the family. The different structures within the genus Vochysia are significant and perhaps demand a reassessment of the botanical classification of one of the species.
Supported by CNPq, CAPES and Fundação Araucária
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