Fructan accumulation

Smeekens, J., Transgenic fructan-accumulating tobacco and potato plants, in Proceedings of the 5th Seminar on Inulin, Fuchs, A., Ed., Carbohydrate Research Foundation, The Hague, 1996, pp. 53-58. 

Sugar beet has been successfully transformed using Jerusalem artichoke-derived 35s-l-sst and 35s-l-fft constructs, incorporating promoters and selection markers, with fructans accumulating in... 

Monti, A., Amaducci, M.T., and Venturi, G., Growth response, leaf gas exchange and fructans accumulation of Jerusalem artichoke (Helianthus tuberosus L.) as affected by different water regimes, Eur. J. Agron.,... 

Accumulation of fructans is enhanced by high light intensity and moderate temperatures. It is reduced by excess nitrogen or insufficient potassium (Soja and Haunold, 1991). Distribution of assimilates initially occurs on the periphery of the stem with subsequent movement inward. The portion of the stem receiving assimilates is dictated by its vascular connections. Radial movement inward is restricted to cells interior to vascular bundles. 

A relatively small amount of reducing inulo- -oses, fructans without a terminal glucose (Ernst et al., 1996), are formed from fructosyl transfer from inulin to free fructose by 1-FFT. In chicory, they are thought to appear when fructose accumulates during fructan breakdown and 1-FFT activity is still high (Van den Ende and Van Laere, 1996). A similar mechanism is probably operative in Jerusalem artichoke and responsible for the small amounts of inulo- -oses formed (Saengthongpinit and Sajjaanantakul, 2005). 

The activities of FBPase, UDPG-pyrophosphorylase, SPS and SS enzymes involved in sucrose biosynthetic pathway were measured at 10 and 25°C in order to explain the accumulation of F6P and G6P at lO C, without concomitant increase in sucrose content, previously found. The activities of all enzymes were lower at the lower temperature, and could not explain the variation in sucrose. However, this can be explained by an increase, of about three times, on the content in fructans at 10°C. 

The final criterion for a prebiotic is that its fermentation in the colon has some beneficial impact on host health. In vitro studies using models of the colonic microbiota inoculated with human feces and studies in animals, have shown that fermentation of prebiotic fructans leads to accumulation of acetate and butyrate in intestinal/gut model contents. Fermentation of other prebiotics and certain dietary fibers has also been shown to increase propionate production in these systems. Small amounts of lactate and succinate can also be observed using in vitro models, but in vivo, these SCFA are rapidly converted into butyrate and propionate by the gut microbiota. Bifidobacteria and lactobacilli ferment carbohydrates mainly to acetate and lactate, but do not themselves produce butyrate. Recent studies have shown that dominant members of the Firmicutes, Eubacterium halli, Roseburia, Faecalibacterium prausnitzii and Anaerostipes caccae are able to cross-feed off acetate and lactate within the colonic milieu converting them into butyrate, providing a mechanism by which prebiotic modulation of acetate-produdng bifidobacteria can lead to elevated butyrate concentrations within the SCFA have been implicated... 

Fmctan is known to accumulate in the tissues of temperate plants during times of cool weather. Since the analysis for fructan is difficult, Chatterton et al. (1989) present a method for the analysis of the synthetic, intermediate fiructosylsucrose. Purified sample extracts were analyzed by HPAEC-PAD with a limit of detection (LOD) of 1 mg/mL. 

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