Organic acid metabolism in aluminum-phosphate utilizing cells of carrot (Daucus carota L.)

Abstract

Carbohydrate metabolism in Al-phosphate utilizing cells of carrot [designated as IPG, Koyama et al. (1992) Plant Cell Physiol. 33: 171], which grow normally in Al-phosphate medium accompanied by citrate excretion, was investigated. The excretion of citrate was strongly related to the availability of sucrose in medium, indicating that citrate excretion was severely limited by sucrose in medium. The ratio of the amount of carbon in the excreted citrate to the consumed sucrose, was significantly higher in IPG cells than in wild-type cells. When 50% of the sucrose in the medium was consumed, the ratio was 0.6% for the IPG cells and 0.2% the wild-type cells. Under these conditions, IPG cells showed altered citrate synthesis metabolism, which resulted in increased citrate production. Specific activity of mitochondrial citrate synthase was higher in IPG cells than in wild-type cells, whereas the activity of cytosolic NADP-specific isocitrate dehydrogenase was lower in IPG cells than in wild-type cells.