Role of ethylene metabolism in Amaranthus retroflexus

14C-Ethylene was metabolized by etiolated pigweed seedlings (Amaranthus retroflexus L.) in the manner similar to that observed in other plants. The hormone was oxidized to 14CO2 and incorporated into 14C-tissue components. Selected cyclic olefins with differing abilities to block ethylene action were used to determine if ethylene metabolism in pigweed is necessary for ethylene action. 2,5-Norbornadiene and 1,3-cyclohexadiene were effective inhibitors of ethylene action at 800 and 6400 microliters per liter, respectively, in the gas phase, while 1,4-cyclohexadiene and cyclohexene were not. However, all four cyclic olefins inhibited the incorporation and conversion of 14C-ethylene to 14CO2 by 95% with I50 values below 100 microliters per liter. The results indicate that total ethylene metabolism does not directly correlate with changes in ethylene action. Additionally, the fact that inhibition of ethylene metabolism by the cyclic olefins did not result in a corresponding increase in ethylene evolution indicates that ethylene metabolism does not serve to significantly reduce endogenous ethylene levels.