Abstract
To determine the origin of organic acids exuded by the roots of P deficient rape plants, phosphoenolpyruvate carboxylase (PEPC) activity was measured in plants after deprivation of P in the nutrient solution. PEPC activity in the shoot increased as a reaction to P stress. This increase coincided with accumulation of citrate in the shoot and with a higher citrate/sugar ratio in the phloem. Application of 14CO2 to the shoots resulted in a ninefold increase in specific activity of organic acids exuded by —P roots as compared with +P roots. These results indicate that exuded organic acids resulted from increased PEPC activity in the shoot of P stressed rape plants.
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