The Effect of 2,4-Dichlorophenoxyacetic Acid on Pathways of Glucose Catabolism in Higher Plants.

Abstract

In a previous communication from this laboratory (8), it was briefly reported that etiolated pea seedlings (cotyledons removed) treated with 2,4-dichlorophenoxyacetic acid (2,4-D) were able to maintain a higher rate of respiration than untreated seedlings. Treatment with 2,4-D did not change the RQ which remained near 1.0. These results suggested that carbohydrate was the major substrate being oxidized in both treated and control seedlings. Subsequent work, as yet unpublished, has shown that 2,4-D treated seedlings did not contain more carbohydrate (reducing sugars, sucrose, and starch) than the untreated seedlings. 2,4-D, then, affects the respiratory rate of pea seedlings without changing the RQ or increasing the carbohydrate level. It would be of interest, therefore, to ascertain whether or not 2,4-D causes glucose to be catabolized via a different pathway, or, if a number of pathways are operative, to cause a change in the amount of glucose catabolized via one of the various pathways. Recently Beevers and Gibbs (2) have shown that the pentose phosphate pathway (oxidative pathway or hexose monophosphate shunt) may be a major route of glucose catabolism in a number of higher plants including peas. On the other hand, these workers obtained evidence by two independent methods <2, 3) that in corn root tips the Embden-Meyerhof-Parnas (E.P.M.) glycolytic pathway is the only operative one. Beevers and Gibbs applied a procedure developed by Bloom and Stetten (4) in which the initial yields of C1402 from tissues supplied with glucose1-C14 (G-l-C14) and glucose-6-C14 (G-6-C14) are compared. If glucose were broken down via the E.M.P. pathway, the rate of Cu02 production from the first and the sixth carbon of the glucose molecule should be the same. If, on the other hand, glucose were broken down via the pentose phosphate pathway the rate of C1402 production from the first carbon of the glucose molecule would initially be greater than that from the sixth carbon. The use of the ratio