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Previously described Rhizobium leguminosarum bv. phaseoli mutants elicit nodules on bean without infection thread formation. These mutants were shown to be purine or, in one case, pyrimidine auxotrophs. Each of the seven purine auxotrophs grew normally when supplied the penultimate precursor of inosine, 5-aminoimidazole-4-carboxamide riboside. Four seemed blocked early in the purine pathway, because they were also thiamine auxotrophs. Reversion analysis and genetic complementation using cloned wild-type DNA showed that in each mutant a single mutation was responsible for both the symbiotic defect and purine or pyrimidine auxotrophy. The mutations were mapped to five dispersed chromosomal locations. The previously reported weak Calcofluor staining of these mutants on minimal agar appeared to be caused by partial growth on contaminating nutrients in the agar, rather than deficient exopolysaccharide production. Nodulation by the mutants was not enhanced by supplying purine or pyrimidine compounds exogenously. Furthermore, with or without added purine, the purine auxotrophs grew in the root environment as well as the wild type. However, nodulation by the purine auxotrophs was enhanced greatly in the presence of 5-aminoimidazole-4-carboxamide riboside. The results suggest that undiminished metabolic flow through de novo purine biosynthesis, or a particular intermediate in the pathway, is essential in early symbiotic interactions.

The electrical and magnetic properties of thex=0.5 composition in the perovskite system La1–xSrxCoO3 , annealed in air at different temperatures, have been investigated. Results from powder XRD, ac magnetic susceptibility, high field and low field (FC and ZFC) dc magnetization, electrical resistivity and EDAX measurements revealed that differences in the properties between the samples annealed at different temperatures (1000–1300 °C) arise due to compositional inhomogeneity. A true compositionally homogeneous compound is formed when annealed in a narrow temperature region close to ca. 1150 °C. A pronounced resistivity anomaly at the Curie temperature with a maximum temperature coefficient of resistance and a well defined magnetic transition are observed for the samples annealed at 1150 °C. The results can explain most of the unusual and widely differing results reported in the literature on the electronic and magnetic properties of different compositions in the La1–xSrxCoO3 system which are synthesized and processed at different temperatures.

Dc magnetization and ac magnetic susceptibility have been measured in the temperature range 80–300 K for La0.7Ca0.3MnO3 , synthesized by the conventional ceramic and the low temperature combustion methods and annealed at different temperatures. Temperature dependence of the dc magnetization and the ac susceptibility is strongly dependent on the processing conditions resulting in compositional inhomogeneity in the samples. A sharp ferromagnetic transition is observed only for a compositionally homogeneous sample.