Fructan matabolism in cereals: induction in leaves and compartmentation in protoplasts and vacuoles
- Zeitschrift fur pflanzenphysiologie, 112(4), p.359-372, 1983 .
Leaf blades of Triticum aestivum L. cv Kolibri and Hordeum vulgare L. cv Gerbel were induced to accumulate fructan (polyfructosylsucrose of varying molecular size)in large amounts (~70 percent of dwt)by impeding the export of photosynthates. This was achieved by sub jecting plants to cold stress (5°C at night)or by continuous illumination of excised leaf blades. Concomitantly with the accumulation of fructan in the leaves the activity of a sucrose sucrose-fructosyltransferase (SST), probably the key-enzyme of fructan anabolism, increased several fold in cell-free extracts. Its pH optimum is 5.7. At 8°C its activity is still half of the activity at 28°C, the temperature optimum. This remarkably anomalous dependence on temperature is interesting with regard to fructan accumulation in grasses during the cold season. Protoplasts obtained from fructan-enriched barley leaves were employed for the isolation of vacuoles. All the fructans (~trisaccharide)as well as the SST activity were found to be asso ciated exclusively with the vacuoles, which therefore appear to play the central role in fructan storage and metabolism.