A Simple Open Flow System Used to Measure Acetylene Reduction Activity of Sesbania rostrata Stem and Root Nodules

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Abstract
A simple method for mixing gases for the assay of acetylene reduction using an open flow system is described. Gas mixtures are obtained using simple regulator valves (described) to obtain equal gas pressures and then providing a resistance to gas flow proportional to the flow of gas required. The system described allows any number of gases to be mixed over a wide range of ratios, at a wide range of flow rates. Using this system, the activity of Sesbania rostrata stem and root nodules was examined in undisturbed plants. Nodules in either location had high rates of acetylene reduction (270 μmol C2H4 g⊟1 DW h⊟1) and showed a decline of approximately 10% in activity after exposure to acetylene. Stem and root nodule activity was similar during the day and night (at a constant temperature) and was dependent on continued phloem connection. Darkening stem nodules during the light period, had little effect on their acetylene reduction activity. These results suggest that the continued supply of sugars via the phloem are important for both stem and root nodule activity.

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