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Changes in carbon metabolism and δ13C 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 phosphoenolpyruvate (PEP), the initial acceptor of CO2 in the C4 photosynthetic pathway. PPDK activities in the leases 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 (r2= 0.81), and was positively correlated with malate content (r2= 0.88). A significant increase in the δ13C 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 C4‐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.

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