Jm. Leah et al., ASSOCIATION BETWEEN ELEVATED ACTIVITY OF ARYL ACYLAMIDASE AND PROPANIL RESISTANCE IN JUNGLE-RICE, ECHINOCHLOA-COLONA, Pesticide science, 42(4), 1994, pp. 281-289
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.