Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Plant Physiology 71:307-312 (1983)
© 1983 American Society of Plant Biologists

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Articles

Amitrole Absorption by Bean (Phaseolus vulgaris L. cv `Red Kidney') Roots 1

Mechanism of Absorption

Francis T. Lichtner2

Department of Botany, University of California, Davis, California 95616

The mechanism of transport of the herbicide 3-amino-1,2,4-triazole (amitrole) into Phaseolus vulgaris roots appears to be passive, as judged by the effect of temperature (Q10 = 1.3 between 15 and 25°C) and the lack of sensitivity to metabolic inhibition afforded by 2,4-dinitrophenol and NaN3. Amitrole absorption is a linear function of external concentration over several orders of magnitude and, thus, is not facilitated by a carrier mechanism. The absorption of amitrole is sensitive to external pH, being stimulated under acid conditions. This stimulation of amitrole absorption is seen at low (≤1 millimolar) amitrole concentrations, but not at high (50 millimolar) amitrole levels. While the apparent octanol-water partition coefficient varies with the pH of the aqueous phase, there is no clear correspondence between absorption and the apparent partition coefficient. Roots do not accumulate amitrole above concentration equilibrium; however, at a time when the net amitrole content of the root tissue begins to saturate, amitrole can be detected in the xylem stream. On a fresh-weight basis, amitrole absorption by roots is equal to that accomplished by trifoliate-leaf tissue. An estimate of the permeability coefficient (according to the analysis of Tyree et al. 1979 Plant Physiol 63: 367-374) suggests that amitrole possesses near-optimal permeability for an ambimobile solute, on the order of 2.12 (± 0.47) x 10–9 meters per second.

2 Present Address: E. I. du Pont de Nemours & Company (Inc.), Biochemicals Department, Experimental Station, Wilmington, DE 19898.

1 Supported in part by a Faculty Research Award from the Division of Graduate Studies and Research, University of California, Davis.






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Copyright © 1983 by the American Society of Plant Biologists