Sugar utilization and invertase activity in hairy-root and cell-suspension cultures of Symphytum officinale

Incomplete consumption of sugars can lead to limited growth of hair roots. To shed light on this phenomenon, growth, sugar consumption, and invertase activity were examined in hairy-root batch cultures of Symphytum officinale L. and in reference cell-suspension cultures of the same species. Sucrose was supplied as sole carbon source. In the hairy-root cultures, sucrose concentration decreased gradually during growth, while glucose and fructose began to accumulate in the medium around day 10. The stationary phase was reached with sugars still present in the medium. Activity of extractable (in vitro) cell-wall-bound invertase increased after day 10 and stayed high throughout the stationary phase. In the cell-suspension batch cultures, sucrose was entirely consumed by the end of culture, while hexoses accumulated till day 7-10 and subsequently declined to zero at day 14: after rising to a peak at day 3. activity of extractable cell-wall-bound invertase declined to a basal level similar to that at day zero. In both types of culture, enzymatic activity seems to have been correlated with hexose concentration, which was high in the early phases of cell batch culture as well as during the stationary phase of hairy-root culture.