THE EFFECTS OF INDOLEACETIC ACID AND 2, 4-DICHLOROPHENOXYACETIC ACID ON INTERMEDIARY METABOLISM OF 14C-LABELLED ORGANIC ACIDS BY PEA ROOT TIPS

Abstract

The effects of indoleacetic acid (IAA) and 2, 4-dichlorophenoxyacetic acid (2, 4-D) on the metabolism of 14C-specifically labelled pyruvic, acetic, succinic, and glutamic acids by pea root tips have been examined. The conversion of 14C from the substrates into alcohol-soluble and -insoluble fractions and respired CO2 was determined, and the radioactivity of certain soluble amino acids and organic acids was measured after chromatography. While pyruvic acid decarboxylation is unaffected, the carboxylation of pyruvic acid and the entry into the Krebs cycle of acetate derived from pyruvate is inhibited by the hormones. Acetate, however, is oxidized to CO2 much more rapidly in the presence of IAA or 2, 4-D. The accumulation of 14C in Krebs cycle intermediates or amino acids derived from them is prevented by the auxins. The results indicate that IAA and 2, 4-D have an inhibiting effect either on co-carboxylase or more likely on α-lipoic acid metabolism, but not on coenzyme A (CoA). Other specific effects on the metabolism of individual amino acids are also indicated.