No abstract

Field experiments were performed in Austria, Brazil, Chile, Colombia, Guatemala, Mexico and Peru as part of an F A O / I A E A Co-ordinated Research Programme to investigate the nitrogen fixing potential of cultivars and breeding lines of common bean (Phaseolus vulgaris L.). Each experiment included approximately 20 bean genotypes which were compared using the 15N isotope dilution method. Great differences in nitrogen fixation were observed between and within experiments, with average values of 35% N derived from atmosphere (% Ndfa) and highest values of 70% Ndfa being observed. These values which were larger than had been reported previously for common bean, were observed only when environmental factors were favorable. Therefore, common bean lines are available, which can support high biological nitrogen fixation. These can be used either directly as cultivars for production or in breeding programmes to enhance nitrogen fixation in other cultivars.

No abstract

The low nodule occupancy achieved by superior nitrogen-fixing inoculant strains is a problem in the production of many traditional legume species, including Phaseolus vulgaris. Cultivars that select for inoculant strains, rather than nodulate with ineffective indigenous rhizobia, offer one approach to the resolution of this problem. In this study we identify a bean cultivar, RAB39, that nodulates preferentially with Rhizobium tropici, including the inoculant-quality strain UMR1899. This preference in nodulation was not affected by temperature or pH, though strain preference by a second, alkaline-producing Rhizobium etli strain did vary markedly with temperature. When RAB39 was inoculated with 1:1 mixtures of UMR1899 and seven serologically distinct strains of Rhizobium etli, more than 75% of the nodules formed by each strain pair contained UMR1899. A number of studies have reported close correlations between the percent nodule occupancy and speed of nodulation, measured using the root-tip-marking procedure. Exceptions to this correlation were evident in the present study, suggesting that host preference in nodulation was not related to differences in the parameters normally used to estimate speed of nodulation. The preference of RAB39 for R. tropici, a species of Rhizobium that occurs at low frequency in most bean soils, and especially for the inoculant-quality strain UMR1899, provides a tool to overcome the lack of response to inoculation in common bean.Resume : La faible occupation des nodositCs rCalisCe par les souches inoculantes fixatrices d'azote constitue un problbme pour la production de plusieurs espbces de 1Cgumineuses traditionnelles, incluant Phaseolus vulgaris. Des cultivars qui ~Clectionnent des souches inoculantes plut6t que de produire des nodositks avec des rhizobia indigbnes inefficaces offrent une approche pour rCsoudre ce problkme. Dans cette Ctude, un cultivar de haricot, le RAB39, qui produit des nodositks de f a~o n prCfCrentielle avec le Rhizobium tropici, incluant la souche de qualit6 UMR1899, a Ct C identifiC. Cette prCfCrence pour la nodulation n'a pas Ct C affectCe par la tempCrature ou par le pH, bien que sa prCfCrence pour une autre souche, une souche productrice alcaline, le Rhizobium etli, ait vari6 de f a~o n marquCe avec la temperature. Lorsque le RAB39 a Ct C inoculC avec des mClanges 1: 1 de UMR1899 et de sept souches s6rologiquement distinctes de Rhizobium etli, plus de 75% des nodositks formCes par chaque paire de souches contenaient le UMR1899. Certaines Ctudes ont rapport6 des corrClations Ctroites entre le pourcentage de nodosit6s et la rapidit6 des nodulations, mesurCe par des marqueurs de pointes racinaires. Des exceptions B cette corrClation ont Ct C Cvidentes dans la prCsente Ctude, ce qui suggbre que la prCfCrence d'un h6te dans la nodulation n'est pas reliCe aux diffkrences de parambtres normalement utilisCs pour Cvaluer la rapidit6 des nodulations. La prCfCrence du RAB39 pour le R. tropici, une espbce de Rhizobium dont la frkquence est faible dans la plupart des sol...

5-Aminolevulinic acid accumulated in the culture medium when Agmeneflum quadplicatum strain PR-6 was incubated in the presence of levulinic acid, a competitive inhibitor of 8-aminolevulinic acid dehydratase, and specifically labeled glutamate and glycine. The 8-aminolevulinic acid was purified using Dowex 50W-X8 and cleaved by periodate to yield succinic acid and formaldehyde. The distribution of radioactivity in the two fragments suggested that in blue-green algae the carbon skeleton of 8-aminolevulinic acid is derived directly from glutamate. However the possibility of the pathway of 8-aminolevulinic acid synthesis, from glycine and succinyl-coenzyme A also functioning in blue-green algae was not eliminated as uptake of glycine was minimal.&-Aminolevulinic acid is the first identified biosynthetic intermediate that is unique to the tetrapyrrole pathway. ALA2 is the precursor of heme in animals (16) and bacteria (9); of Chl in bacteria (6) and plants (8); and of the phycobilins in red algae (19). In many organisms ALA is formed by the condensation of glycine and succinyl-CoA, catalyzed by ALA synthetase, a pyridoxal-requiring enzyme. The enzymatic activity was first demonstrated in photosynthetic bacteria (12) and chicken erythrocytes (7). ALA synthetase has since been reported in yeast, bacteria, and a number of animal tissues. However, workers have been unable to demonstrate conclusively ALA synthetase activity in green plants and green algae (2).In studies in which cucumber cotyledons (3), bean and barley leaves (4), maize leaves (15), and the unicellular rhodophyte Cyanidium caldarium (10) were incubated in the presence of levulinic acid and labeled compounds; glutamate, a-ketoglutarate, and glutamine were found to donate label to the ALA that accumulated, much more effectively than glycine. Furthermore, from the specific pattern of incorporation of label into ALA, it appears that ALA is formed from the intact carbon skeleton of glutamate in a manner incompatible with the ALA synthetase route (1,5,10,15).Herein, we report the labeling of ALA from specifically labeled glutamate by a blue-green alga. The evidence suggests that bluegreen algae synthesize ALA from glutamate in a manner similar to that observed in green plants and green algae.