Specific effects of fructo- and gluco-oligosaccharides in the preservation of liposomes during drying.

The fructan family of oligo- and polysaccharides is a group of molecules that have long been implicated as protective agents in the drought and freezing tolerance of many plant species. However, it has been unclear whether fructans have properties that make them better protectants for cellular structures than other sugars. We compared the effects of fructans and glucans on membrane stability during air-drying. Although glucans of increasing chain length were progressively less able to stabilize liposomes against leakage of aqueous content after rehydration, fructans showed increased protection. On the other hand, glucans became more effective in protecting liposomes against membrane fusion with increasing chain length, whereas fructans became less effective. Fourier transform infrared spectroscopy showed a reduction of the gel to liquid-crystalline phase transition temperature (T(m)) of air-dried liposomes by approximately 25 degrees C in the presence of sucrose and maltose. For the respective pentasaccharides, the reduction of T(m) of the lipids was 9 degrees C lower for samples containing fructan than for those containing glucan, indicating increased sugar--membrane interactions for the fructan compared to the glucan. A reduced interaction of the longer-chain glucans and an increased interaction of the respective fructans with the phospholipid head groups in the dry state was also indicated by dramatic differences in the phosphate asymmetric stretch region of the infrared spectrum. Collectively, our data indicate that the fructo-oligosaccharides accumulated in many plant species under stress conditions could indeed play an important role in cellular dehydration tolerance.