Mode of action of naphthalic anhydride as a safener for the herbicide AC 263222 in maize
✍ Scribed by Davies, Joanna; Caseley, John C.; Jones, Owen T. G.; Barrett, Michael; Polge, Nicholas D.
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 314 KB
- Volume
- 52
- Category
- Article
- ISSN
- 1526-498X
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✦ Synopsis
In hydroponic experiments, seed-dressing with the herbicide safener 1,8-naphthalic anhydride (NA), signiÐcantly enhanced the tolerance of maize, (Zea mays L., cv. Monarque) to the imidazolinone herbicide, AC 263222, (2-[4isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-5-methylnicotinic acid). Uptake, distribution and metabolism studies where [14C]AC 263222 was applied through the roots of hydroponically grown maize plants showed that NA treatment reduced the translocation of radiolabel from root to shoot tissue and accelerated the degradation of this herbicide to a hydroxylated metabolite. Reductions in the lipophilicity and, therefore, mobility of this compound following hydroxylation may account for NA-induced retention of radiolabel in the root system. Hydroxylation of AC 263222 suggested that NA may stimulate the activity of enzymes involved in oxidative herbicide metabolism, such as the cytochrome mono-oxygenases. In agreement with this theory, the cytochrome P 450 P 450 inhibitor, 1-aminobenzotriazole (ABT), synergized AC 263222 activity and inhibited its hyroxylation in vivo. NA seed-dressing enhanced the total cytochrome and content of microsomes prepared from etiolated maize shoots. Iso-P 450 b 5 lated microsomes catalyzed AC 263222 hydroxylation in vitro. This activity possessed the characteristics of a cytochrome mono-oxygenase, being P 450 NADPH-dependent and susceptible to inhibition by ABT. Activity was stimulated four-fold following NA seed treatment. Di †erential NA enhancement of AC 263222 hydroxylase and the cytochrome cinnamic acid-4-P 450
-dependent hydroxylase (CA4H) activity, suggested that separate isozymes were P 450 responsible for each activity. These results indicate that the protective e †ects of NA result from enhancement of AC 263222 hydroxylation and concomitant reduction in herbicide translocation. This may be attributed to the stimulation of a microsomal cytochrome system. 1998 SCI. P 450