Vol. 15—1961 - NorthEastern Weed Science Society

15.
not find an abundant production .0£ C 14 02 but rather an incorporation of the
radiocarbon into plant const~tuents. T61s was brought home forcibly in the
study of the metabolism of the triazine herbicides by trees and shrubby l'lants.
Ap?reciable quantities of radiocarbon would be found in the leaves but u P9 extraction
with the use of solvents to fractionate the radioactivity, the C l 4n was
found to be widely distributed in many fractions.
Similarly differences in the ability of a given plant 8J?ecies to metabolize
different trlazines was not~d. A major difference in rates of cl40 2
production
by corn when eXi'osed to the different chlorine eontaining alkylamino triazines
has been found.
Summary and Conclusions
Scattered published reports clearly indicate that ~lants like animals and
microorganisms are fully capable of metabolic attack on organic chemicals to .
which they are exposed in their environment. Again, parallel with animals or
microorganisms, the plant may carry out this metabolic attack by one of several
means. The metabolism may take the form of a conjugation of the externally ailPl1ed
chemical with proteins or carbohydrates or with simpler compounds such as amino
acids and the sulfur-containing amino acids. Similarly the compounds may undergo
hydrolysis, hydroxylation and other chemical modifications. Of particular interest
in this paper has been the matter of the plant's ability to carry out oxidation
of externally applied materials. .It has been shown'by the experimental
work reported that plants possess the ability to oxidize such chemicals as ami~
trole and amiben, 2,4-DB and the triazine herbicides. The evidence for this
oxidation rests on the evolution of the radioactive carbon dioxide and the ap)earance
of the C14 in normal plant constituents. .
Metabolism of herbicides may be shown to be related to the mode of action of
the drug. This comes about in the first instance where an innocuous compound is
converted by the illant's metabolism to a compound of high biological potency, thus
killing the plant or modifying its growt~ In the second instance, the metabolism
helps to reduce the toxicity of the compound and may serve in part at least as a
basis of the tolerance of the plant toward the chemical. Complete oxidation of
the compound to innocuous products is of importance at the practical level in that
this serves to reduce,the residue of that c6mpound. The initial steps in the
sequence of reactions leading to complete OXidation of the triazine herbicides
has been partially worked out. The reactions have been shown to be dependent upon
enzymes leading to organically unstable molecules.
This preliminary re~ort attem)ts to summarize some of the information on
metabolism of herbicides. It is hoped that this modest effort will serve as a
stimulus to additional worlt in this field and the elucidation of complete mechanisms
by which many of the herbicides are metabolized by plants.
Literature
Cited
1. Andreae, W. Po. and Good, N. E., Plant Physiol. lQ, 3£10, 1955.
2. Audus, L. J., Plant Growth Substances, 2nd Ed., Leonard Hill Books Ltd,
London, 1959.
3. Butts, J. S. and Fang, S. Co, Radioactive Isotopes in Mtriculture, AEC RetJort,
No. TID 7512, p. 209, 1956.