Abstract

The effects of CDAA (N,N-diallyl-2-chloroacetamide) pretreatment on subsequent CDAA injury to corn were examined and compared with the effects of the herbicide protectant R-25788 (N,N,-diallyl-2,2-dichloroacetamide). In addition, the effects of CDAA pretreatment on subsequent CDAA metabolism were determined. It was found that 5μM CDAA protected corn from injury by 200 μM CDAA when given as a 2.5- or 1-day pretreatment. R-25788 at similar concentrations did not protect corn from subsequent R-25788 injury. Pretreatment with CDAA increased GSH levels of corn roots by 61% within 1 day, and these levels did not increase with a longer 2.5-day pretreatment with CDAA. GSH-S-transferase activity was assayed spectrophotometrically using CDNB (1-chloro-2,4-dinitrobenzene). A 1-day pretreatment with CDAA increased the root GSH-S-transferase activity by 35%, but did not affect shoot GSH-S-transferase activity. A 2.5-day pretreatment resulted in a 50% increase in root GSH-S-transferase activity but no response of the shoot enzyme was observed. Even longer pretreatments with CDAA did not result in any further increases in enzyme activity. When corn roots pretreated with CDAA for 2.5 days were excised and incubated with radiolabeled CDAA, they exhibited greater rates of uptake and metabolism than did nonpretreated roots. With in vitro studies, a fairly high rate of nonenzymatic degradation of CDAA was observed. However, the enzymatic rate was always double that of the nonenzymatic rate under the experimental conditions used. It is concluded that elevations in the GSH levels and GSH-S-transferase activities of corn roots following CDAA pretreatments may be involved in the protection of corn from subsequent CDAA injury.

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