Nitrogenase activity in root nodule homogenates ofAlnus incana

Summary

Root nodule homogenates of actinorhizal plants may representFrankia in a symbiotic stage but released from environmental influence of the host plant. Anaerobic homogenization with a blender in buffer supplied with sucrose, polyvinylpyrrolidone and reducing substances gave three times higher yields of nitrogenase activity (C₂H₂-reduction) than crushing the nodules in liquid nitrogen. The activity in the homogenates was very reproducible and was, on average, nearly twice as high as the activity in excised nodules and c. 10% of the activity in intact plants. The difference in activity between excised nodules and intact plants was, roughly by halves, due to removal of the root system from the pot and to excision of the nodules. The nitrogenase activity in the homogenates was slightly higher when nodule excision was done in Ar or under water as well as after treatment of the homogenate with toluene or Triton X-100 or osmotic shock. These gains in activity were considered too small to outweigh the increased complications of preparing homogenates for routine use. Due to the reproducible recovery of nitrogenase in the homogenates the technique seems useful for physiological studies on nitrogen fixation inAlnus incana.