Acetate Utilization by Maize Roots

Abstract

Acetate-1-C14 or acetate-2-C14 was supplied to root tips excised from 2-day-old corn seedlings. The progress of C14O2 evolution was followed at intervals of 1 minute and the progressive contribution of C14 from the acetate to various metabolites was determined. After 30 seconds 98% of the alcohol soluble C14 was present in organic acids (other than acetate) and the percentage declinded to about 50 at 30 minutes as the percentage of C14 in amino acids (principally glutamic and aspartic acids and their amides) rose from 0 to 50 during the same periods. No incorporation into the neutral (sugar) fraction occurred. Kinetic experiments showed clearly that citrate was the first of the acids of the TCA cycle to be -come labeled; C14 appeared subsequently in succinate and later in malate. Parallel experiments showed that C14O2 began to appear from roots provided with acetate-l-C14 only after a lag corresponding to the time for the production of malate- C14, and that from roots provided with acetate-2-C14 showed a considerably greater lag. The results provide new and definitive evidence for the view that the TCA cycle is the all important pathway in the oxidation of acetate to CO2 in this tissue.