Metabolism of 2,4-Dichlorophenoxyacetic Acid in 2,4-Dichlorophenoxyacetic Acid-Resistant Soybean Callus Tissue

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Abstract
Three 2,4-D-resistant root callus tissue lines of G. max L. Merrill cv. Acme were derived by culturing callus tissue 2-6 mo. on 40 mg/l 2,4-D and designated 40R, 40B and 40C. Tissue line 40R had a lower level of 2,4-D uptake in 2-wk-old tissue which disappeared in 3.5-wk-old tissue and less free 2,4-D following incubation for 24 h with [1-14C]2,4-D. This tissue line accumulated more hydroxylated glycosides of 2,4-D than did nonresistant tissue. Tissue line 40B showed no difference in uptake of 2,4-D when compared to nonresistant tissue but it did contain less free 2,4-D and more hydroxylated glycosides. The metabolism of 2,4-D in the 40C tissue line did not differ significantly from nonresistant tissue although uptake was less. The 40R line reverted to the same 2,4-D sensitivity as cv. Acme root callus following 6 transfers on 10 .mu.M naphthaleneacetic acid medium. The altered 2,4-D uptake and metabolism characteristic of 40R were also lost. The levels of amino acid conjugates of 2,4-D in the resistant root callus tissue lines were either lower or not significantly different from the cv. Acme tissue lines. Apparently, variations in uptake and metabolism of 2,4-D do not wholly explain the resistance of the derived tissue lines and modification of the active site or compartmentation may be involved.

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