RESUMEN
In addition to the storage function, fructans in Asteraceae from floras with seasonal growth have been associated with drought and freezing tolerance. Vernonia herbacea, native of the Brazilian Cerrado, bears underground reserve organs, rhizophores, accumulating inulin-type fructans. The rhizophore is a cauline branched system with positive geotropic growth, with the apex (distal region) presenting younger tissues; sprouting of new shoots occurs by development of buds located on the opposite end (proximal region). Plants induced to sprouting by excision of the aerial organs present increased 1-fructan exohydrolase (1-FEH) activity in the proximal region, while plants at the vegetative stage present high 1-sucrose:sucrose fructosyltransferase (1-SST) in the distal region. The aim of the present study was to analyze how low temperature (5 degrees C) could affect fructan-metabolizing enzymes and fructan composition in the different regions of the rhizophores of intact and excised plants. 1-SST and 1-fructan:fructan fructosyltransferase (1-FFT) were higher in the distal region decreasing towards the proximal region in intact plants at the vegetative phase, and were drastically diminished when cold and/or excision were imposed. In contrast, 1-FEH increased in the proximal region of treated plants, mainly in excised plants subjected to cold. The ratio fructo-oligo to fructo-polysaccharides was significantly higher in plants exposed to low temperature (1.17 in intact plants and 1.64 in excised plants) than in plants exposed to natural temperature conditions (0.84 in intact vegetative plants and 0.58 in excised plants), suggesting that oligosaccharides are involved in the tolerance of plants to low temperature via 1-FEH, in addition to 1-FFT. Principal component analysis indicated different response mechanisms in fructan metabolism under defoliation and low temperature, which could be interpreted as part of the strategies to undergo unfavorable environmental conditions prevailing in the Cerrado during winter.
