Biological Characterization of Root Exudates and Extracts from Nonnodulating and Supernodulating Soybean Mutants. Anne Mathews. Botany Department, Australian National University, Canberra ACT 2601, Australia. Renee M. Kosslak(3), Champa Sengupta-Gopalan(2), Edward R. Appelbaum(3), Bernard J. Carroll(1), and Peter M. Gresshoff(1,4). (1)Botany Department, Australian National University, Canberra ACT 2601, Australia. (2)Plant Genetic Engineering Laboratory, New Mexico State University, Las Cruces 88003 U.S.A. (3)Agrigenetics Advanced Science Corporation, Madison, WI 53716 U.S.A. (4)Plant Molecular Genetics, Institute of Agriculture, University of Tennessee, Knoxville 37901-1071 U.S.A. MPMI 2:283-290. Accepted 16 May 1989. Copyright 1989 The American Phytopathological Society.

The root exudates and extracts of soybean nonnodulation (nod¯) mutants nod49, nod139, and nod772 were compared with those of the wild-type parent cultivar Bragg and supernodulation (nitrate tolerant symbiotic) mutant nts382 to assess their effects on the early stages of nodulation by Bradyrhizobium japonicum strain USDA110. When nod¯ mutants were cocultured in proximity with wild-type or mutant nts382, nodulation was as expected for the individual genotypes. Coculturing nts382 with wild-type or nonnodulating plants decreased nodule number on the supernodulating mutant when compared to similar plant density of nts382 alone. Pretreatment of B. japonicumwith collected root exudates of the soybean mutants did not affect nodulation efficiency or total nodule number per plant. Analysis of in vivo labeled proteins in root exudates of wild type, nts382, and nod49 showed similar patterns both on one- and two-dimensional gels. Radioactively (³⁵S) labeled root exudates were subjected to immunoprecipitation with the antibody to soybean lectin (SBL) and similar amounts were found in the nod49, nts382, and wild-type soybean. Seedling root extracts of nts382, nod49, and Bragg were tested for their ability to induce a nodC::lacZ fusion in B. japonicum strain USDA110. Similar levels of induction were found in all cases, indicating that uninoculated seedlings of cultivar Bragg, nod49, and nts382 contained similar stimulating compounds. Based on the observation that mutants nod49, nod139, and nod772 lack root hair curling, we suggest that the nonnodulation phenotype may be caused by an inability to respond efficiently to bacterial factors designed to stimulate plant cell divisions and concomitant root hair curling.