Comparative Metabolism of 2,4-Dichlorophenoxyacetic Acid in Cotyledon and Leaf Callus from Two Varieties of Soybean

Only quantitative differences were observed in the metabolism of 1-(14)C2,4-dichlorophenoxyacetic acid (2,4-D) by soybean cotyledon callus as influenced by variety (Acme and Amsoy), source of tissue (cotyledon, leaf and root) and age. All tissues metabolized 2,4-D to water-soluble (glycosides) and ether-soluble (primarily amino acid conjugates) metabolites.In young (3- to 4-week-old) Amsoy cotyledon or leaf callus tissue the free 2,4-D increased proportionately with the external 2,4-D concentration while in older (6- to 8-week-old) tissue the amino acid conjugates increased in this manner. Thus, in the older Amsoy tissue apparent regulation of the internal 2,4-D level (1.5-3.5 nmoles per gram fresh weight) was observed. In 3- or 6-week-old Acme cotyledon callus 2,4-D accumulated with an increase in the external 2,4-D concentration with no evidence for regulation of internal 2,4-D levels.