Rapid decarboxylation of the products of dark fixation of CO 2 in roots of pisum and Plantago

Abstract

Seedlings of Pisum sativum and excised roots of Plantago major and P. lanceolata were given, in the dark, a pulse of 14CO 2 in air followed by a chase in 12CO 2 in air. A very substantial proportion of the 14C fixed into organic compounds in the pulse was lost from the tissues in the chase. The activity of NAD malic enzyme in extracts of roots of all three species exceeded their rate of respiration. Azide, 2- n-butylmalonate, and salicylhydroxamic acid each inhibited CO 2 fixation by excised roots of pea. The first two compounds inhibited respiratory gas exchange, but the third stimulated it. Arguments are presented for the widespread diversion of phosphoenolpyruvate from glycolysis to oxaloacetate and thence to malate in the cytosol followed by transport of the malate into the mitochondria for conversion to pyruvate via NAD malic enzyme. No differences, in the above respects, were found between the two species of Plantago.