WATER-STRESS LEADS TO A CHANGE OF PARTITIONING IN FAVOR OF SUCROSE IN HETEROTROPHIC CELL-SUSPENSION CULTURES OF CHENOPODIUM-RUBRUM

When heterotrophic cell suspension cultures of Chenopodium rubrum were subjected to water stress by incubation in increasing concentrations of sorbitol there was an immediate shrinking of the protoplast volume. Glucose uptake decreased in parallel. When the external water potential was greater than 0.5 MPa, a change in the partitioning of this incoming carbon was observed, resulting in a doubling of the ratio of sucrose to starch. This was accompanied by an increase in the concentration of the glycolytic intermediates and a particularly pronounced increase in the levels of fructose-2,6-bisphosphate and malate. The extractable activity of sucrose phosphate synthase was determined using a new method which overcomes the problem of uridine-diphosphate loss from the assay medium. It was found that sucrose phosphate synthase activity decreased in the water stressed cells. Therefore, the higher sucrose concentration in these cells is attributed to the increase in metabolite concentrations alone.