ELEVATED PYRUVATE,ORTHOPHOSPHATE DIKINASE (PPDK) ACTIVITY ALTERS CARBON METABOLISM IN C-3 TRANSGENIC POTATOES WITH A C-4 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 pyr uvate (PEP), the initial acceptor of CO2 in the C-4 photosynthetic pat hway. PPDK activities in the leaves of transgenic potatoes were up to 5.4-fold higher than those of control potato plants (wild-type and tre ated control plants). In the transgenic potato plants, PPDK activity i n leaves was negatively correlated with pyruvate content (r(2) = 0.81) , and was positively correlated with malate content (r(2) = 0.88). A s ignificant increase in the delta(13)C value was observed in the transg enic potato plants, suggesting a certain contribution of PEP carboxyla se as the initial acceptor of atmospheric CO2. These data suggest that elevated PPDK activity may alter carbon metabolism and lead to a part ial operation of C-4-type carbon metabolism. However, since parameters associated with CO2 gas exchange were not affected, the altered carbo n metabolism had only a small effect on the total photosynthetic chara cteristics of the transgenic plants.