The acetylene-induced decline in nitrogenase activity in root nodules of Elaeagnus angustifolia

Abstract

The rate of C2H2 reduction by nodulated seedlings of Elaeagnus angustifolia (Russian olive) was followed as a function of time. Our goals were to: 1) determine whether there is an C2H2-induced decline in nitrogenase activity; and 2) investigate the mechanism of any decline. We found a peak rate of C2H2 reduction at 1.5 min after the introduction of C2H2 that was followed by a rapid decline in activity to 56% of the peak value. After the decline there was a partial recovery to 67% of the peak value at 60 min. When the pO2 was decreased during the decline there was no significant effect (p≤0.05) on nitrogenase activity. When the C2H2 reduction assay was preceded by an incubation in a gas mixture (20 kPa O2) with Ar substituted for N2, there was little decline in nitrogenase activity as a function of time, but the rate of C2H2 reduction per gram nodule was reduced by approximately 50%. From these results we conclude that t Elaeagnus angustifolia exhibits a pronounced C2H2-induced decline and consequently the initial peak rate C2H2 reduction must be determined to obtain a valid measure of nitrogenase activity. We further suggest that cessation of NH3 formation initiates the decline and that the decline is not caused by a change in nodule permeability to gases.