About 15% of flowering plants accumulate fructans. Inulin-type fructans with b(2,1) fructosyl linkages typically accumulate in the core eudicot families (e.g. Asteraceae), while levan-type fructans with b(2,6) linkages and branched, graminan-type fructans with mixed linkages predominate in monocot families. Here, we describe the unexpected finding that graminan-and levan-type fructans, as typically occurring in wheat (Triticum aestivum) and barley (Hordeum vulgare), also accumulate in Pachysandra terminalis, an evergreen, frost-hardy basal eudicot species. Part of the complex graminan-and levan-type fructans as accumulating in vivo can be produced in vitro by a sucrose:fructan 6-fructosyltransferase (6-SFT) enzyme with inherent sucrose:sucrose 1-fructosyltransferase (1-SST) and fructan 6-exohydrolase side activities. This enzyme produces a series of cereal-like graminan-and levan-type fructans from sucrose as a single substrate. The 6-SST/6-SFT enzyme was fully purified by classic column chromatography. In-gel trypsin digestion led to reverse transcription-polymerase chain reaction-based cDNA cloning. The functionality of the 6-SST/6-SFT cDNA was demonstrated after heterologous expression in Pichia pastoris. Both the recombinant and native enzymes showed rather similar substrate specificity characteristics, including peculiar temperature-dependent inherent 1-SST and fructan 6-exohydrolase side activities. The finding that cereal-type fructans accumulate in a basal eudicot species further confirms the polyphyletic origin of fructan biosynthesis in nature. Our data suggest that the fructan syndrome in P. terminalis can be considered as a recent evolutionary event. Putative connections between abiotic stress and fructans are discussed.About 45,000 species of angiosperms, approximately 15% of the flowering plants, store fructans, Fru-based oligo-and polysaccharides derived from Suc. Fructans are known to occur in the highly evolved orders of the Poales (Poaceae), Liliales (Liliaceae), Asparagales, Asterales (Asteraceae and Campanulaceae), and Dipsacales as well as within the Boraginaceae (Hendry, 1993). Fructans are believed to accumulate in the vacuole (Wiemken et al., 1986), although fructans and fructan degrading enzymes (fructan exohydrolases [FEHs]) have also been reported in the apoplast (Livingston and Henson, 1998;Van den Ende et al., 2005). To explain this observation, it was hypothesized that fructans can be transferred from the vacuole to the outer side of the plasma membrane by vesicle-mediated exocytosis (Valluru et al., 2008, and refs. therein), especially under stress. Fructans might protect plants against freezing/drought stresses (Valluru and Van den Ende, 2008) by stabilizing membranes (Vereyken et al., 2001;Hincha et al., 2002Hincha et al., , 2003. Recent studies on transgenic plants carrying fructan biosynthetic genes (Parvanova et al., 2004;Li et al., 2007;Kawakami et al., 2008) suggest that the enhanced tolerance of these plants is associated with the presence of fructans. Their reduced lipid p...

Summary We investigate whether an increase in the occurrence of cyanobacterial blooms affects zooplankton–parasite interactions. Cyanobacteria are expected to be of poor food quality for zooplankton hosts and are therefore expected to increase parasitism. Nevertheless, simultaneous exposure to both stressors may lead to different results, given the antibacterial secondary metabolites of cyanobacteria. We exposed the zooplankter Daphnia magna to the cyanobacterial species Microcystis aeruginosa and the parasite that causes white bacterial disease in D. magna. Increased M. aeruginosa concentrations reduced the percentage of infected individuals and as such protected D. magna against parasitism. Interactions between M. aeruginosa and the parasite were antagonistic in terms of percentage of surviving Daphnia, total offspring per female and clutch size. Additional plating experiments showed a direct negative effect of Microcystis on bacterial growth. The results suggest that changes in phytoplankton affect host–parasite interactions in zooplankton. Contrary to the prevailing paradigm that multiple stressors often induce additive or synergistic effects, we report an antagonistic effect of the presence of cyanobacterial stress on parasites in Daphnia. Thus, assessment of the outcome of host–parasite interactions needs to incorporate the environmental context.

Fructans are known to occur in 15% of flowering plants and their accumulation is often associated with stress responses. Typically, particular fructan types occur within particular plant families. The family of the Buxaceae, harboring Pachysandra terminalis, an accumulator of graminan- and levan-type fructans, also harbors boxtree (Buxus sempervirens), a cold and drought tolerant species. Surprisingly, boxtree leaves do not accumulate the expected graminan- and levan-type fructans, but small inulin fructo-oligosaccharides (FOS: 1-kestotriose and nystose) and raffinose family oligosaccharides (RFOs: raffinose and stachyose) instead. The seasonal variation in concentrations of glucose, fructose, sucrose, FOS and RFOs were followed. Raffinose and stachyose peaked during the winter months, while FOS peaked at a very narrow time-interval in spring, immediately preceded by a prominent sucrose accumulation. Sucrose may function as a reserve carbohydrate in winter and early spring leaves. The switch from RFO to fructan metabolism in spring strongly suggests that fructans and RFOs fulfill distinct roles in boxtree leaves. RFOs may play a key role in the cold acclimation of winter leaves while temporal fructan biosynthesis in spring might increase sink strength to sustain the formation of new shoots.