PHYSIOLOGICAL-ROLE OF THE PROPANIL HYDROLYZING ENZYME (ARYL ACYLAMIDASE-I) IN RICE PLANTS

With the view of studying the physiological role of the propanil hydrolyzing enzyme (aryl acylamidase I), a comparison was made between the propanil susceptible rice mutant, which lacks the enzyme activity, and normal rice. Also, the properties of rice treated with a carbamate insecticide, a strong aryl acylamidase I inhibitor, were examined. The growth of the rice mutant was repressed approximately twice as much as that of the normal one by ammonium sulfate and urea. The mutant rice accumulated twice as much free ammonia as the normal one in the shoots under a high nitrogen supply. m-Tolyl methylcarbamate (MTMC) was used as the inhibitor of the enzyme. The growth of normal rice treated with MTMC was repressed 20% by ammonium sulfate but that of untreated rice was not affected at all. The propanil susceptible rice mutant, which lacks the activity of aryl acylamidase I and has higher susceptibility to ammonium sulfate by nature, showed no changes after MTMC treatment. The rice mutant is also more susceptible to a microb-originated herbicide bialaphos, l-2-amino-4-[(hydroxy)(methyl)phosphinoyl]butyryl-l-alanyl-alanine, of which the mode of action is assumed to be ammonia accumulation, than the normal one. The mutant was controlled 50% by the foliar application of 40 ppm bialaphos but normal rice was not affected at all at this concentration. Furthermore, twice as much free asparagine was found in the mutant rice than in the normal rice. Accordingly, it is suspected that aryl acylamidase I plays an important role in the normal nitrogen metabolism relating asparagine in rice plants. © 1991.