INFECTION AND DEVELOPMENT OF SYMBIOTIC NITROGENFIXING ACTINORHIZA OF CORIARIA NEPALENSIS WALL.

Frankia hyphae penetrate root ha rs and invade root cortical cells of Coriaria nepalensis Wall., leading to nodulation. Owing to the stimulation caused by infection, a part of the cortical cells in the infected root divide and hypertrophy, resulting in the formation of a prenodulein which the nodule primordium develops. The primordium divides and differentiates, forming a primary nodule lobe. The apical meristem of a lobe hranchs dichotomously and the branchings develop with the infection of new host cells by the endophytes, giving rise to a coralloid root nodule consisting of many dichotomic branchings. In cross section, the endophyte-infected tissue zone in a lobe is a horse-shoeshaped compactmass, incompletely surrounding the acentral stele. In longitudinal section, the apical part of a mature lobe is the meristem, followed successively by the non-infected tissue, the newly infected tissue, the mature infected tissue and the senescent infected tissue. The lobal stele is surrounded by several layers of cortical cells containing starch granules.