Oxygen Supply and Energy-yielding Substrates for Nitrogen Fixation (Acetylene Reduction) by Bacteroid Preparations

Sucrose and glucose supported acetylene reduction by bacteroids extracted from Frenchbean, soybean and pea root nodules in the presence of low O2 concentrations in experiments carried out with or without a gas phase, but not under O2 tensions usually able to support acetylene reduction with succinate. Addition of leghaemoglobin to the bacteroid suspensions allowed maximum rates of ethylene formation at very low O2 concentrations (1 to 5 nm) when sucrose or glucose was present in assays with no gas phase. Stimulation of bacteroid O2 consumption was lower with these carbohydrates than with succinate for a similar acetylene reduction activity. This low O2 uptake provided O2 steady-state conditions in gas phase experiments. The optimal O2 tension required for bacteroid acetylene reduction was lower when nodule age increased.