In vitro culture and fructan production by Vernonia herbacea (Asteraceae)

Vernonia herbacea is a native species from the Brazilian Cerrado that accumulates about 80 % of inulin-type fructans in the underground reserve organs, the rhizophores. This work aimed at establishing a protocol for in vitro culture of V. herbacea, using seeds (achenes) and leaf discs as explants. Following germination and seedling growth, stem nodes from 6-month-old in vitro germinated plants were isolated and incubated on culture medium free of growth regulators for plant propagation and rhizophore formation. Fructan content and composition were evaluated in leaves, stems, roots and rhizophores from plants grown in vitro and compared with those of greenhouse-grown plants, in order to evaluate inulin production in vitro. Fructan contents of aerial organs and roots from in vitro plants were higher, compared with greenhouse plants, while in rhizophores, the opposite was observed. High performance anion exchange chromatography/pulsed amperometric detection profiles revealed the presence of the inulin homologous series in the aerial organs exclusively for in vitro plants, while in roots and rhizophores, this series was detected in plants grown in both conditions. These results indicate a modification in the source/sink ratio, leading to changes in the distribution of carbohydrates in in vitro plants. The leaf disc cultures on medium supplemented with indole-3-butyric acid induced the formation of roots (0.24, 0.49 A mu M) and friable callus (2.46 A mu M), while 6-benzylaminopurine (from 1.1 through 4.43 A mu M) induced compact callus. However, no shoot formation was observed. The use of seeds allowed the establishment of a protocol for in vitro culture and provides a model system for a better understanding of fructan metabolism in V. herbacea.