Cells Expressing ENOD2 Show Differential Spatial Organization During the Development of Alfalfa Root Nodules. Ted Allen. Department of Biology, Boston College, Chestnut Hill, MA 02167 U.S.A. Sandhya Raja, and Kathleen Dunn. Department of Biology, Boston College, Chestnut Hill, MA 02167 U.S.A. MPMI 4:139-146. Accepted 23 October 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991.

We have used in situ hybridization to examine the spatial organization of cells expressing the early nodulin gene (ENOD2) during the development of alfalfa root nodules. ENOD2 gene expression was found in the nodule parenchyma, uninfected cells surrounding the symbiotic region of both effective and ineffective nodules. However, in empty nodules, ENOD2 gene expression was found in a mass of parenchyma cells at the base of the nodule. Similar results were also observed in 11-day-old nodules that contained infected cells but that had not yet begun to express leghemoglobin. Although early events of nodulation result in the induction of ENOD2 expression in cells at the nodule base, the pattern of cells expressing ENOD2 during nodule growth appears to be correlated with the development of other peripheral tissues.