Dark CO₂ Fixation and its Role in the Growth of Plant Tissue

Experiments were designed to determine the significance of dark CO(2) fixation in excised maize roots, carrot slices and excised tomato roots grown in tissue culture. Bicarbonate-(14)C was used to determine the pathway and amounts of CO(2) fixation, while leucine-(14)C was used to estimate protein synthesis in tissues aerated with various levels of CO(2).Organic acids were labeled from bicarbonate-(14)C, with malate being the major labeled acid. Only glutamate and aspartate were labeled in the amino acid fraction and these 2 amino acids comprised over 90% of the (14)C label in the ethanol-water insoluble residue.Studies with leucine-(14)C as an indicator of protein synthesis in carrot slices and tomato roots showed that those tissues aerated with air incorporated 33% more leucine-(14)C into protein than those aerated with CO(2)-free air. Growth of excised tomato roots aerated with air was 50% more than growth of tissue aerated with CO(2)-free air. These studies are consistent with the suggestion that dark fixation of CO(2) is involved in the growth of plant tissues.