Root nodule initiation in Gymnostoma (Casuarinaceae) and Shepherdia (Elaeagnaceae) induced by Frankia strain HFPGpI1

RACETTE, S., and TORREY, J. G. 1989. Root nodule initiation in Gymnostoma (Casuarinaceae) and Shepherdia (Elaeagnaceae) induced by Frankia strain HFPGpIl. Can. J. Bot. 67: 2873-2879. Seedlings of Gymnostoma papuanum (Casuarinaceae) and Shepherdia argentea (Elaeagnaceae) were grown in water culture and inoculated with Frankia strain HFPGpIl. Root nodule initiation and early nodule development were examined using light microscopy. Gymnostoma papuanum was infected by penetration of Frankia into deformed root hairs, followed by development of a prenodule region and one to several nodule lobe primordia in the root cortex. Frankia hyphae grew directly through cell walls from cell to cell, colonizing cells of the prenodule prior to invading nodule lobe cells. Shepherdia argentea roots were infected by Frankia via intercellular penetration of the root epidermis and cortex with direct infection of cells of the nodule lobe primordia. No prenodule region was formed. Thus far, the mode of infection appears to be characteristic for each of the plant families. Subsequent to nodule initiation, plants were assayed at 4-week intervals (up to 12 or 16 weeks) for acetylene reduction activity. Low and variable activity was observed. The presence of symbiotic vesicles in G. papuanum nodules is reported as the first instance of vesicles seen in nodules taken from a member of the family Casuarinaceae.