IN-VITRO CONJUGATION OF CHLOROACETANILIDE HERBICIDES AND ATRAZINE WITH THIOLS AND CONTRIBUTION OF NONENZYMATIC CONJUGATION TO THEIR GLUTATHIONE-MEDIATED METABOLISM IN CORN
I. Jablonkai et Kk. Hatzios, IN-VITRO CONJUGATION OF CHLOROACETANILIDE HERBICIDES AND ATRAZINE WITH THIOLS AND CONTRIBUTION OF NONENZYMATIC CONJUGATION TO THEIR GLUTATHIONE-MEDIATED METABOLISM IN CORN, Journal of agricultural and food chemistry, 41(10), 1993, pp. 1736-1742
The contribution of nonenzymatic conjugation of acetochlor, alachlor,
metolachlor, pretilachlor, and atrazine with glutathione (GSH) in the
metabolism of these herbicides by roots and shoots of the Cargill 7567
and Northrup-King 9283 hybrids of corn (Zea mays L.) was investigated
. Treatment with 50 muM of each herbicide revealed the following order
of chloroacetanilide phytotoxicity: acetochlor > alachlor > metolachl
or > pretilachlor. Atrazine did not injure any of the corn hybrids. Ca
rgill 7567 was more tolerant than Northrup-King 9283 to metolachlor an
d pretilachlor, but the two corn lines did not differ in their respons
e to acetochlor and alachlor. Total nonprotein thiol, GSH, and cystein
e contents were similar in the two corn hybrids. Glutathione S-transfe
rase (GST) activities were comparable in the two corn hybrids. Chloroa
cetanilide-specific GST activities were 2-4-fold greater in roots than
in shoots of either hybrid, and enzymatic conjugation with GSH was mo
re efficient with acetochlor and alachlor than with metolachlor and pr
etilachlor as substrates. Assays on the in vitro chemical reactivities
of acetochlor, alachlor, metolachlor, pretilachlor, and atrazine with
GSH and cysteine revealed that the higher the ratio of thiol to herbi
cidal substrate concentrations, the higher the amount of conjugate for
med. Nonenzymatic conjugation with GSH may contribute significantly to
the overall glutathione-mediated metabolism of chloroacetanilide herb
icides and atrazine in corn and seems to be dependent on the concentra
tion and molecular structure of the herbicidal substrate as well as on
the GSH content of plant tissues (root vs shoot).