ASSOCIATION BETWEEN ELEVATED ACTIVITY OF ARYL ACYLAMIDASE AND PROPANIL RESISTANCE IN JUNGLE-RICE, ECHINOCHLOA-COLONA

Aryl acylamidase (aryl-acylamine amidohydrolase, EC 3.5.1.13) activity has been measured in crude extracts from leaves of propanil-susceptib le (S) and propanil-resistant (R) biotypes of the grass weed, Echinoch loa colona (L.) Link from Columbia. Both specific and total amidase ac tivity increased with plant age up to 15 days (four-leaf stage), then decreased beyond 20 days to about 50% of the maximum at 36 days in bot h R and S E. colona biotypes. Specific activity with propanil in the R biotype was about 80% of that obtained for rice (Oryza sativa L.), co mpared to 25% in the susceptible biotype. The specific activity of the propanil amidase was three-fold higher in the R biotype than in the S . Partially purified amidase extracts from rice and both S and R bioty pes of E. colona were compared biochemically. Both rice and E. colona amidases had a pH optimum of 7.5 and native relative molecular masses, estimated by gel filtration, of 179 000 and 181 000, respectively. Ou t of six substrates tested, three produced appreciable activity (propa nil, 4-chloroacetanilide and acetanilide) in both rice and E. colona. Michaelis constants showed that the rice amidase had a higher affinity for propanil (0.36 mM) than had the E. colona enzyme (1.1 mM). Carbam ates and organophosphorus pesticides were shown to inhibit amidase act ivity in partially purified rice and E. colona extracts. Additional pr eliminary data have implicated peroxidase in the next step of propanil metabolism in vitro. These data demonstrate that increased aryl acyla midase activity contributes to resistance to the herbicide propanil in E. colona weeds. Also, a biochemical comparison of purified aryl acyl amidases from S and R biotypes of E. colona is presented for the first time.