Impact of CGA-136872 and EPTC on enzymatic and growth characteristics of CGA-136872-tolerant and -susceptible corn (Zea mays L.) varieties

Abstract

A technique was developed to expose corn seedlings to EPTC, a volatile herbicide, or CGA-136872, a non-volatile herbicide. This technique was used to document the cross tolerance of a CGA-136872-tolerant variety, Funk G4673A, to EPTC. The CGA-136872-susceptible variety, Funk G43Q7, had significantly more injury from EPTC than Funk G4673A, as indexed by tissue length, fresh weight, and soluble protein content. All tissues of Funk G4307 were reduced more in growth than those of Funk G4673A by CGA-136872 treatments ranging from 0.0625 to 1 μg/ml. The mesocotyl lengths of Funk G4673A were unaffected by a 0.5 μg/ml treatment of CGA-136872, whereas the mesocotyl length of Funk G4307 was reduced 71%. Although 2000-μg of EPTC caused a significant reduction in mesocotyl growth of Funk G4307, Funk G4673A was unaffected by this rate of treatment. The soluble protein content of coleoptile tissue of Funk G4673A was unaffected by CGA-136872, whereas there was a linear (r-square=0.99) increase in soluble protein content of Funk G4307 with increasing rate of CGA-136872 treatment. The soluble protein content of coleoptile tissue of both varieties increased linearly with increased rates of EPTC, with r-square values of 0.94 and 0.96 for Funk G4307 and Funk G4673A, respectively. A 4000 μg treatment of EPTC elevated soluble protein content significantly more in Funk G4307 than Funk G4673A. Treatment of either variety with EPTC or CGA-136872 significantly elevated glutathione-S-transferase (GST) activity of one or more of the tissues treated. Although GST appears to be involved in the metabolism of these two herbicides, it does not seem to be involved in a mutual mechanism of cross tolerance. Nomenclature: EPTC, S-ethyl dipropylcarbamothioate; CGA-136872, [2-[[[[[4,6-bis (difluoromethoxy)-2-pyrimidinyl] amino] carbonyl] amino] sulfonyl] benzoic acid]; corn, Zea mays L.