PHOTOSYNTHESIS AND METABOLISM OF ORGANIC ACIDS IN HIGHER PLANTS

The importance of organic acids as photosynthetic intermediates, first suggested by Liebig, has been subject to speculation for over100 years. The free organic acids or their phosphate esters still are included in the most recent schemes for photosynthetic assimilation of carbon dioxide (8, 12). Recent advances in our knowledge of the path of carbon in photosynthesis have been described so adequately (3, 8, 9, 12), that any extensive review of the subject here is unwarranted. BENNET-CLARK (2) recently has reviewed the literature on the organic acids of plants. Our early attempts to use higher plants for the biosynthesis of C14-labeled organic acids (7) revealed that equilibrium in C14 distribution among the organic acids was not established even many hours after exposure to C1402. The observed concentration of C14 in malic acid suggested the possible importance of this acid as an early photosynthetic product. Accordingly, the distribution of C14 among several organic acids from plants supplied C1402 was investigated.