Te. Kraus et al., MODULATION OF ETHYLENE SYNTHESIS IN ACOTYLEDONOUS SOYBEAN AND WHEAT SEEDLINGS, Journal of plant growth regulation, 11(1), 1992, pp. 47-53
The characteristics of ethylene production and ACC conversion in 8-day
-old soybean seedlings were examined and a relationship between cytoch
rome P-450 activity and ethylene-forming enzyme (EFE) activity was fou
nd. An atmosphere containing 10% carbon monoxide (CO) significantly in
hibited ethylene production and ACC conversion in control soybean seed
lings, but had only a slight effect on soybean seedlings treated with
uniconazole. Foliar application of triclopyr, a pyridine analogue of t
he phenoxy herbicides, significantly increased ethylene production and
ACC conversion in control, but not in uniconazole-treated seedlings.
Triclopyr treatment also resulted in a three-fold increase in extracta
ble cytochrome P-450 of 5-day-old etiolated soybeans. At equimolar con
centrations tetcyclacis was more effective than uniconazole in reducin
g shoot elongation and endogenous ethylene production. Although unicon
azole and tetcyclacis did not inhibit ACC conversion in nonherbicide-t
reated soybean seedlings, they did prevent the observed increase in AC
C-dependent EFE activity following triclopyr application. However, the
rate of ACC conversion in etiolated soybean segments was sensitive to
uniconazole, and tetcyclacis inhibited the rate of ACC conversion by
2.6-fold in etiolated soybean segments within 4 h after treatment. Mic
rosomal membranes were isolated from 5-day-old naphthalic anhydride-tr
eated etiolated wheat shoots as this tissue contains much higher cytoc
hrome P-450 levels than soybean shoots. Optical difference spectroscop
y demonstrated that ACC generated binding spectrum characteristic of a
reverse-type-I cytochrome P-450 substrate when combined with reduced
microsomes. In vitro conversion of ACC to ethylene by microsomal membr
anes was NADPH-dependent, inhibited by CO, and had an apparent K(m) an
d V(max) of 45-mu-M and 0.345 nl/mg protein/h, respectively. These res
ults suggest that cytochrome P-450-mediated monooxygenase reactions ma
y be intimately involved in the conversion of ACC to ethylene in young
soybean and wheat seedlings.