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Contribution of Nonautotrophic Carbon Dioxide Fixation to Protein Synthesis in Suspension Cultures of Paul's Scarlet Rose

^a Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73069

Bicarbonate-¹⁴C was provided to 5- and 11-day-old suspension cultures of Paul's Scarlet rose, and the incorporation of ¹⁴C into lipid, protein, amino acids, and organic acids was determined. The rate of bicarbonate uptake was approximately the same by 5- and 11-day-old cells, but the distribution of ¹⁴C among cell constituents was markedly different. In 5-day-old cells a larger proportion of the ¹⁴C entered protein, whereas in 11-day-old cells there was a greater tendency for ¹⁴C to accumulate in malate.

The ¹⁴C in protein was distributed among 10 amino acids each having greater than 1% of the total ¹⁴C recovered in protein. The distribution of ¹⁴C among tricarboxylic acid cycle intermediates indicated that the aspartate family of amino acids was synthesized directly from oxaloacetate produced as a result of nonautotrophic CO₂ fixation. However, this was not the sole source of oxaloacetate used for the synthesis of aspartate, for in a double labeling study with bicarbonate-¹⁴C and acetate-³H it was shown that oxaloacetate was drained simultaneously from the tricarboxylic acid cycle for this purpose.