The underground reserve organs of yacon (Polymnia sonchifolia Poep. Endl.), similarly to other economically important Asteraceae, accumulate more than 60%, on a DW basis, of inulin type β(2‐1) fructans, mainly oligomers (GF2–GF16). Although sucrose:sucrose 1‐fructosyl transferase (1‐SST), fructan:fructan 1‐fructosyl transferase (1‐FFT) and fructan 1‐exohydrolase (1‐FEH) were properly described and characterized from a number of plant species, detailed information about their activities in different organs during development are rather scarce in the literature. In the present work 1‐SST, 1‐FFT and 1‐FEH activities were measured monthly in rhizophores and tuberous roots of yacon plants during their complete growth cycle under field conditions. Results showed that 1‐SST activity in rhizophores was always higher than 1‐FFT activity and increased up to 8 months of cultivation, decreasing to initial values at the end of the growth period. In the tuberous roots 1‐SST activity was also higher than 1‐FFT but varied differently. The higher values were found at the beginning of tuberization (3‐month‐old plants) and at the flowering phase (7‐month‐old plants). Results also showed that synthesizing activities in yacon plants were always higher in rhizophores than in the tuberous roots, while hydrolysing activity predominated in the latter, mainly when 1‐kestose and nystose were used as substrates. 1‐FEH from yacon plants showed low efficiency when commercial inulin from Helianthus tuberosus was utilized as substrate. The analysis of the enzymatic activities performed during growth of yacon clearly indicated the most appropriate source organ and phase of development to obtain the highest enzymatic activities for purification purposes and for the production of fructo‐oligosaccharides (FOS). Furthermore, the results suggested that the relative levels of activities of 1‐SST, 1‐FFT and 1‐FEH could be involved in the chain length distribution of the fructan molecules found in rhizophores and in tuberous roots of this species.

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Sucrose:sucrose fructosyltransferase (SST) and fructan:fructan fructosyl-transferase (FFT) activities from crude extracts of tuberous roots of Viguiera discolor growing in a preserved area of cerrado were analyzed in 1995-1996. SST activity was characterized by the synthesis of 1-kestose from sucrose and FFT activity by the production of nystose from 1-kestose. The highest fructan-synthesizing activity was observed during early dormancy (autumn), when both (SST and FFT) activities were high. The increase in synthetic activity seemed to start during the fruiting phase in the summer, when SST activity was higher than in spring. During winter and at the beginning of sprouting, both activities declined. The in vitro synthesis of high molecular mass fructans from sucrose by enzymatic preparations from tuberous roots collected in summer showed that long incubations of up to 288 h produced consistently longer polymers which resembled those found in vivo with respect to chromatographic profiles.

In order to evaluate the involvement of fructans in drought tolerance

SUMMARYTuberous roots of Viguiera discolor accumulate up to 80% of their dry mass as fructans. The distribution pattern of oligomers suggests the predominance of anabolic reactions at the beginning of dormancy, when a continuous series of fructans between sucrose and higher polymers is present. This paper describes the synthesis in vitro of fructans of high molecular mass by enzyme extracts prepared from growing tuberous roots of V. discolor at the beginning of dormancy. Sucrose: sucrose fructosyl transferase activity was characterized by the synthesis of 1-kestose from sucrose and fructan: fructan fructosyl transferase activity by the production of nystose from 1-kestose. The optimal temperature for both activities was 30 °C and the optimal pH range was between 5-5 and 6-0. The apparent K^ for sucrose with respect to 1-kestose synthesis was 173 mol m^^, whereas the K^.^ for nystose synthesis from 1-kestose was much higher (592 mol m"^^). Long incubation periods (up to 264 h) with sucrose, 1-kestose or nystose produced fructans of high molecular mass in vitro that resembled those found in vivo. Our data show that the higher the molecular mass of the substrate, the higher the average molecular mass of the product that u'as formed.