No abstract

Fructans, a family of oligo- and polyfructoses, are implicated to play a drought-protecting role in plants. Inulin-type fructan is able to preserve the membrane barrier during dehydration. However, whether other fructans would be able to perform this function is unknown. In addition, almost nothing is known about the organization of these systems, which could give insight into the protective mechanism. To get insight into these questions the effect of different fructans on phosphatidylcholine-based model systems under conditions of dehydration was analyzed. Using a vesicle leakage assay, it was found that both levan- and inulin-type fructans protected the membrane barrier. This suggests that fructans in general would be able to protect the membrane barrier function. Furthermore, both fructan-types inhibited vesicle fusion to a large extent as measured using a lipid-mixing assay. Using x-ray diffraction, it was found that in the presence of both inulin- and levan-type fructans the lamellar repeat distance increased considerably. From this it was concluded that fructans are present between the lipid bilayers during drying. Furthermore, they stabilize the L(alpha) phase. In contrast to fructans, dextran did not increase the lamellar repeat distance and it even promoted L(beta) phase formation. These data support the hypothesis that fructans can have a membrane-protecting role during dehydration, and give insight into the mechanism of protection.

Self-aggregation of rigid-rod poly(sodium p-phenylenesulfonate) in aqueous solution and inside water-swollen polyacrylamide gel was studied by small-angle neutron scattering. It was shown that both inside the hydrogel and in solution polyelectrolyte rods self-assemble into cylindrical aggregates having eight to nine single polymer chains in the cross-section, the chains being aligned parallel to the axis of the aggregate. The length of these aggregates is much higher than the contour length of a single chain. Gels with embedded rods were studied by contrast variation method in order to examine separately the scattering by the gel and by the rods. Two important observations were made. First, it was shown that the ordering of the rods in the gel resembles that in solution. Second, it was shown that the gel itself is more homogeneous in the presence of rods. Most probably, this effect is due to mobile counterions of rods, which counteract the formation of spatial inhomogeneities in the network during synthesis, because in an inhomogeneous network mobile counterions should be also distributed nonuniformly that is associated with significant translational entropy losses.