Effects of 2,4-Dichlorophenoxyacetic Acid on Enzymes of Glycolysis & Pentose Phosphate Cycle

Abstract

Etiolated corn (Zea mays L.) seedlings (3-day old) were divided into 2 groups and treated either with phosphate buffer, 10-2 [image], pH 5.3, or with buffer plus 2,4-dichlorophenoxyacetic acid (2,4-D), 10-3 [image], for 12 hours at 22[degree]C. Cell-free extracts and acetone powder extracts were prepared from the roots of each group of seedlings and used to study glycolytic enzymes and the pentose phosphate cycle. Individual enzymes were studied in reaction mixtures containing excess substrate plus the known cofactors, with enzyme concentration being the limiting factor of the reaction. It was found that the activities of 6-phosphofructokinase, aldolase, and glyceraldehyde-3-phosphate dehydrogenase were decreased in extracts from 2,4-D treated tissue, while the activities of phosphoglucoisomerase, phosphoglyceric kinase, and enolase were not affected. Studies of pyruvic kinase and phosphoglyceric mutase were inconclusive. The activities of glucose-6-phosphate dehydrogenase and 6-phosphoglyconate dehydrogenase were increased in extracts from 2,4-D treated tissue. In extracts from 2,4-D treated tissue there was an increased utilization of ribose-5-phosphate and an increased formation of heptulose and hexose. These in vitro studies support the observation that 2,4-D increases the amount of glucose catabolized via the pentose phosphate cycle in intact corn roots.