Graduate Thesis Or Dissertation
 

Some factors affecting absorption and translocation of phenoxyalkylcarboxylic acids in plants

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  • Studies were conducted to determine the influence of formulation and molecular configuration of some chlorinated-phenoxyalkylcarboxylic acid herbicides on their absorption, translocation and metabolism in bigleaf maple, Acer macrophyllum, Pursh. Five to eight year old bigleaf maple seedlings were treated with one percent solutions of carbon 14-labeled herbicids. After three days the treated leaves were washed with alcohol and the plant sectioned into the treated leaves, new growth, stem and roots. A test of the acids, triethanol amine salts and 2-ethylhexyl esters of 2,4-D and 2,4,5-T revealed an inverse relationship between molecular polarity and absorbability within herbicides. The translocation of the various formulations and chemicals were influenced to a large degree by the amount absorbed. The translocatability of the acids and the amine salts were similar while the ester formulations were lower. In terms of actual amounts of chemical translocated to the roots, however, 2,4,5-T ester was most effective A study of the 2-ethylhexyl ester of 2,4-D, 2,4,5-T, 2,4-DP and 2,4,5-TP revealed some trends in absorbability. In general, the alpha-phenoxypropionic herbicides were absorbed to a greater degree than the phenoxyacetic herbicides. Between herbicides of equal side chain length, the dichlorinated member was more readily absorbed than the trichlorinated member. The translocatability of these various herbicides from the treated leaves was not significantly different. However, the movement into the roots differed significantly among chemicals. In terms of actual amounts of herbicide translocated to the roots, the following decreasing order was observed: 2,4-DP, 2,4,5-T, 2,4-D and 2,4,5-TP. It is believed that chemical toxicity to the transport mechanism, absorption by the phloem parenchyma cells and leakage to the xylem influenced herbicide movement to the roots, Studies of the: metabolism of 2,4-D, 2,4,5-T, 2,4-DP and 2,4,5-TP in single detached bigleaf maple leaves revealed that decarboxylation was not an important means of detoxification in this species. Paper chromatograms prepared from alcohol extracts of these leaves showed only limited formation of metabolites. The metabolism of 2,4-D and 2,4,5-T in intact seedlings, however, showed various plant parts have a greater ability to alter the form of the applied chemical than the treated leaves. Differences in the rate of chemical alteration between 2,4-D and 2,4,5-T were also observed in the same plant part. It was shown that 2,4,5-T was more stable than 2,4-D in most plant parts. The stability of 2,4,5-T in the roots was considered of importance in determining the relative effectiveness of these two herbicides on bigleaf maple. Studies of the absorption, translocation and metabolism of 2,4-DB in bigleaf maple were also conducted. It was shown that detached bigleaf maple leaves rapidly decarboxylated 2,4-DB. Absorption and translocation studies revealed slightly reduced absorption compared to the other herbicides tested, but it was markedly superior in translocatability. Gas chromatography was used to establish that the primary product of oxidation of 2,4-DB in bigleaf maple was 2,4-D. These tests also indicated the form of the translocated material was 2,4-DB rather than its oxidation product, 2,4-D. Studies using excised root and stem tissue revealed the roots were capable of rapidly converting 2,4-DB to 2,4-D. The stems had only a limited ability to perform this conversion. It is felt the garnma-phenoxybutyric herbicides may have a valuable place in control of some brush species which have resisted control with aerial application of 2,4-D and 2,4,5-T.
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