Inhibition of potato tuber sprouting: Low levels of cytosolic pyrophosphate lead to non-sprouting tubers harvested from transgenic potato plants

Expressing E. coli inorganic pyrophosphatase in transgenic plants demonstrated that long distance sucrose transport is dependent on cytosolic pyrophosphate. It was speculated that removal of cytosolic pyrophoshate would impair sucrose utilization during storage of potato tubers and thereby prevent tuber sprouting. To explore this hypothesis Solanum tuberosum var. Desiree plants were transformed with a chimeric PPa gene. Following Agrobacterium mediated transformation, metabolite and carbohydrate contents of growing and stored tubers were measured. There was a large accumulation of soluble sugars and a decrease of starch at all developmental stages investigated. The PPase activity in PPaII tubers was parallel with a decrease of PPa, an increase of fructose-2,6-bisphosphate and an increase of UDP-glucose. As expected the amount of hexose-6-phosphates and glycolytic intermediates decreased. As a consequence PPaII tubers did not sprout even after a prolonged storage period of two years. Since the energy status of PPaII tubers is unaltered inhibition of sprouting is most likely due to reduced sucrose export and its subsequent utilization.