Elevated pyruvate,orthophosphate dikinase (PPDK) activity alters carbon metabolism in C3 transgenic potatoes with a C4 maize PPDK gene

Changes in carbon metabolism and delta(13)C value of transgenic potato plants with a maize pyruvate, orthophosphate dikinase (PPDK: EC 2.7.9.1) gene are reported, PPDK catalyzes the formation of phosphoenol pyruvate (PEP), the initial acceptor of CO2 in the C-4 photosynthetic pathway. PPDK activities in the leaves of transgenic potatoes were up to 5.4-fold higher than those of control potato plants (wild-type and treated control plants). In the transgenic potato plants, PPDK activity in leaves was negatively correlated with pyruvate content (r(2) = 0.81), and was positively correlated with malate content (r(2) = 0.88). A significant increase in the delta(13)C value was observed in the transgenic potato plants, suggesting a certain contribution of PEP carboxylase as the initial acceptor of atmospheric CO2. These data suggest that elevated PPDK activity may alter carbon metabolism and lead to a partial operation of C-4-type carbon metabolism. However, since parameters associated with CO2 gas exchange were not affected, the altered carbon metabolism had only a small effect on the total photosynthetic characteristics of the transgenic plants.