Respiration and nitrogenase activity in nodules of Casuarina cunninghamiana and cultures of Frankia sp. HFP020203: Effects of temperature and partial pressure of O sub(2)

Acetylene reduction by the nodules increased rapidly as temperature was increased between 6 and 26 degree C. Between 26 and 36 degree C there was relatively little effect of temperature on acetylene reduction. Nodules and cultures of Frankia were compared with respect to the effect of temperature and pO sub(2) (partial pressure of oxygen) on oxygen uptake. Cultures of Frankia) were grown on a nitrogen-free medium at either 0.3 kPa O sub(2) (vesicles absent) or 20 kPa O sub(2) (vesicles present). Oxygen uptake by nodules (vesicles absent) and by vesicle-containing cultures was strongly dependent on pO sub(2) at values below 20 kPa. Respiration by cultures of Frankia) lacking vesicles became O sub(2)-saturated at low pO sub(2) values. Thus these cultures did not have a significant diffusion barrier. It is concluded that nodules of Casuarina cunninghamiana) have a barrier to oxygen diffusion supplied by the host tissue and not by Frankia .