Development of Phaseolus vulgaris Root Nodules. Rosarita Tate. International Institute of Genetics and Biophysics, CNR, Via Marconi 12, 80125 Naples, Italy. Eduardo J. Patriarca, Anna Riccio, Roberto Defez, and Maurizio laccarino. International Institute of Genetics and Biophysics, CNR, Via Marconi 12, 80125 Naples, Italy. MPMI 7:582-589. Accepted 25 May 1994. Copyright 1994 The American Phytopathological Society.

We report developmental studies on the determinate type of root nodules in Phaseolus vulgaris induced by Rhizobium leguminosarum biovar phaseoli. We show the first steps of nodule induction, leading to the formation of the nodule primordium from cells of the root outer cortex and describe the development of the central tissue, including invaded and uninvaded cells. Cytological observations, such as cell size and the pattern of starch accumulation, show that cells of the central tissue arc a heterogeneous population. In situ hybridization shows a specific pattern of expression of the leghemoglobin and uricase-II genes. In mature nodules older invaded cells appear to be located in coincidence with a window generated in the endodermis by the penetration of the infection threads in the central tissue. This region seems to be the eccentric origin of a radial gradient of development. A model for the development of the common bean nodule is proposed.