Vol. 54—2000 - NorthEastern Weed Science Society

MODE OF ACTION, ABSORPTION, TRANSLOCATION AND
METABOLISM OF MESOTRIONE IN WEEDS AND CORN
B. A. Lackey', R. A. Wichert', D. W. Bartleif', and J. K. Townson'
ABSTRACT
Mesotrione (ZA1296) is an experimental triketone (2-benzoylcyclohexane-1,3-diones)
herbicide being developed for preemergence and postemergence weed control in corn.
The molecular target for ZA 1296 is the enzyme p-hydroxyphenylpyruvate dioxygenase
(HPPD). This enzyme is involved in the pathway that converts the amino acid tyrosine
to plastiquinone. ZA 1296 is structurally similar to the substrate p­
hydroxyphenylpyruvate and acts by competttive inhibttion which results in the blockage
of carotenoid synthesis. Radiolabelled mesotrione was used to study foliar uptake and
translocation in com and weeds at intervals ranging from 1 hour to 7 days after
application. Foliar uptake of mesotrione is rapid, with 30 to 90% of applied radioactivity
absorbed wtthin 6 hours of application, depending on species. Progression of uptake
with time varied with species, but by one day after treatment uptake into common
lambsquarters (Chenopodium album L.) was greater than in giant foxtail (Setaria faberi
Herrm.) and ivyleaf momingglory [Ipomoea hederacea (L.) Jacq.]. Uptake of radiolabel
by com was less than uptake by the weeds evaluated. Phosphor image analysis of
radiochemical at 1 and 7 days after treatment showed both xylem and phloem
movement. Recovery of parent mesotrione, as a percentage of the total extractable
radioactivtty that moved out of the treated leaf, ranged from 10 to 42% in weeds and
none was recovered in com. Differential sensitivity of com and weeds are explained by
differences in uptake and metabolism.
'ZENECA Ag Products, Macedon, NY; 'ZENECA Ag Products, Richmond, CA;
and 'ZENECA Ag Products, Jealott's Hill, UK.
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