XVI International Botanical Congess

Frankia induces root nodules, actinorhiza, on more than 200 angiosperms useful in soil restoration and in various types of forestry. Variations, determined by the host, are seen in infection pathway, morphology and anatomy of nodules and in differentiation of Frankia cells in nodules. Nitrogenase in Frankia is localized in vesicles, except for Casuarina and Allocasuarina nodules where only filaments (hyphae) are formed. Both nodulation and nitrogen fixation are influenced by environmental factors. In Alnus, nitrogen fixation in field responded to weather conditions during and prior to the day of measurement. Dynamics in nitrogen fixation was followed from the whole plant level to nitrogenase protein level in nodules, and decreased activity was ascribed to loss of nitrogenase proteins. Unlike legume nodules, Alnus nodules are not oxygen limited and Frankia itself appears able to protect nitrogenase from oxygen inactivation.