Carbon dioxide effects on fruits : III. The fixation of C(14)O 2 in lemon in an atmosphere enriched with carbon dioxide.

1. The first products of C(14)O2 fixation by lemon fruit in the dark were found to be malic, citric and aspartic acids. It is presumed that exalacetic is actually the first product to be labeled but that it is converted rapidly to the three other acids. 2. Malonic acid was identified as one of the products of exposure to C(14)O2. 3. Aconitic, fumaric and α-ketoglutaric acids could not be detected in the extracts of lemon peel, thus raising the possibility of the existence of at least two pools for the products of CO2 fixation. 4. The suggestion was advanced that accumulation of citric acid in the vacuole leads to a deficiency of oxalacetic acid and thus limits overall oxidation. Carbon dioxide stimulates respiration by increasing the supply of oxalacetic acid.