Naphthalic Anhydride Induces Imazethapyr Metabolism and Cytochrome P-450 Activity in Maize*

Naphthalic anhydride is a seed-applied herbicide safener which reduces the toxicity of ima­ zethapyr, an imidazolinone herbicide, to maize (Zea mays L.). Protection of maize from ima­ zethapyr was dependent on the amount of naphthalic anhydride applied to the seed. M etabo­ lism of imazethapyr by maize roots and shoots was increased by exposure of the roots to a solution containing naphthalic anhydride. Increased imazethapyr metabolism due to naph­ thalic anhydride treatment o f roots was observed within 4 h following safener exposure. N itro­ gen, carbon monoxide and tetcyclacis inhibited imazethapyr metabolism in maize coleoptiles grown from naphthalic anhydride treated seed. This suggests that imazethapyr is metabolized by a cytochrome P-450 monooxygenase. Naphthalic anhydride application to maize seed increased the level of cytochrome P-450 in the seedling shoots. Microsomes isolated from coleoptiles grown from naphthalic anhydride treated seed, but not untreated seed, converted bentazon to hydroxy-bentazon but did not me­ tabolize imazethapyr. Protection of maize from imazethapyr damage by naphthalic anhydride is due to a safener-induced higher rate of imazethapyr metabolism associated with elevated cytochrome P-450 levels. However, this was not demonstrated in vitro for imazethapyr.