Localization of Lipoxygenase Proteins and mRNA in Pea Nodules: Identification of Lipoxygenase in the Lumen of Infection Threads. Christopher D. Gardner. Department of Genetics, John Innes Centre, Colney Lane, Norwich NR4 7UH, U.K. D. Janine Sherrier, Igor V. Kardailsky, Nicholas J. Brewin. Department of Genetics, John Innes Centre, Colney Lane, Norwich NR4 7UH, U.K. MPMI 9:282-289. Accepted 13 February 1996. Copyright 1996 The American Phytopathological Society.

Antibody and nucleic acid probes were used to investigate the localization of lipoxygenase in pea nodules. The an-tiserum identified several proteins in immunoblots of nodule extracts after polyacrylamide gel electrophoresis. These proteins co-migrated with previously characterized pea seed lipoxygenases. When nodule tissue sections were examined by immunogold labeling, a novel extracyto-plasmic location for lipoxygenase antigen was identified in the subapical invasion zone: the antigen was found in the lumen of Rhizobium-inductd infection threads. Immunogold labeling was also observed in the cytoplasm of cells in the nodule periphery. This labeling was heaviest at the nodule apex, outside the meristematic region. There was also labeling in the vicinity of nodule vascular tissue where phloem companion cells were found to contain lipoxygenase antigen. An RNA probe derived from a genomic clone of a pea lipoxygenase gene was used for in situ hybridization studies on pea nodule sections. The expression pattern observed was broadly consistent with the distribution of the protein antigen as observed by immunogold localization. This multiplicity of localizations suggests that several lipoxygenases are present in pea nodules and that they may have a multiplicity of functions relating to plant-microbe interactions, tissue differentiation, and nitrogen storage.