GENETIC MANIPULATION OF 6-PHOSPHOFRUCTOKINASE IN POTATO-TUBERS

The aim of this work was to discover whether genetic manipulation of 6 -phosphofructokinase [EC 2.7.1.11; PFK(ATP)] influenced the rate of re spiration of tuber tissue of Solanum tuberosum L. Transgenic plants we re produced that contained the coding sequence of the Escherichia coli pfkA gene linked to a patatin promoter. Expression of this chimaeric gene in tubers resulted in a 14- to 21-fold increase in the maximum ca talytic activity of PFK(ATP) without affecting the activities of the o ther glycolytic enzymes. Tubers, and 'aged' disks of tuber tissue, fro m transformed plants showed no more than a 30% fall in the content of hexose 6-monophosphates; the other intermediates of glycolysis increas ed three- to eightfold. Fructose-2,6-bisphosphate was barely detectabl e in aged disks of transformed tubers. The relative rates of (CO2)-C-1 4 production from [1-C-14]- and [6-C-14]-glucose supplied to disks of transformed and control tubers were similar. Oxygen uptake and CO2 pro duction by aged disks of transformed tubers did not differ significant ly from those from control tubers. The same was true of CO2 production , in air, and in nitrogen, for tuber tissue. It is concluded that PFK( ATP) does not dominate the control of respiration in potato tubers.