Legume Symbiosis Research Articles

Fertilizer‐N Effects on N2 Fixation by Cowpea and Soybean1

AbstractWhile it is established that high levels of combined N inhibit the development and function of legume root nodules, the application of low‐level “starter” doses of fertilizer‐N is sometimes recommended to improve nodulation and N2 fixation in the long term. The amounts of combined N which are required to optimize legume symbiosis are poorly defined. Before screening a number of rhizobial isolates for effectiveness with cowpea [Vigna unguiculata (L.) Walp.] we set out to determine what levels of fertilizer‐N are optimal for symbiosis in pot conditions.We examined the effects of fertilizer‐N applied at or soon after sowing, on nodulation, N, fixation and growth of two cultivars of cowpea and, for comparison one of soybean [Glycine mar (L.) Merr.] in the greenhouse. Two experiments were done to examine (a) the effects of fertilizer N before flowering and (b) the effects of fertilizer‐N throughout the growth cycle and on final yield. The levels of N found to stimulate symbiosis during the pre‐flowering period were an order of magnitude higher than those previously reported. Applications of 36 and 72 mg N/plant increased nodule weights and acetylene reduction activities up to fourfold and sixfold, respectively, but trends varied with legume host and time of harvest. When 30, 90, 180, or 360 mg N/plant were applied as NH4NO3, KNO3, or urea, symbiotic responses again varied and no single N treatment was optimal for all three legumes. Synergistic effects of applied N on total amounts of N fixed were observed with each host with various N treatments. The strongest synergism occurred in soybean with urea at 30 mg N/plant; for every milligram of urea‐N absorbed, an additional 15 mg of N were fixed symbiotically.

Revertible hydrogen uptake-deficient mutants of Rhizobium japonicum

We have developed mutants of Rhizobium japonicum which are deficient in H2 uptake capacity (Hup-) and which spontaneously revert to the parent type at a frequency consistent with that of a single-point mutation (ca. 1.0 x 10(-09)). The mutagenesis by nitrous acid and the selection of the Hup- phenotype by using penicillin and chemolithotrophy as enrichment for chemolithotrophy-deficient strains are described. Two mutants retain low but reproducible levels of ribulose bisphosphate-dependent CO2 fixation when grown on a low-carbon medium under an atmosphere of 1% O2, 4% H2, 5% CO2, and 90% N2. Neither O2 nor the artificial electron acceptors phenazine methosulfate or methylene blue supported detectable H2 uptake by the free-living Hup- mutants or by their bacteroids. Plant growth experiments under bacteriologically controlled conditions were conducted to assess the mutants' performance as inocula for soybean plants. Plants inoculated with Hup- strains had lower dry weights and contained less total N than did plants inoculated with the parent Hup+ strain. Use of either the Hup- mutants or the Hup+ parent strain as inocula, however, did not significantly affect the acetylene-reducing activity or the fresh weight of nodules. These results, obtained with apparently isogenic lines of H2 uptake-deficient R. japonicum, provide strong support for a beneficial role of the H2 uptake phenotype in legume symbiosis.

The Respiratory Costs of Nitrogen Fixation in Soyabean, Cowpea, and White Clover

The Respiratory Costs of Nitrogen Fixation in Soyabean, Cowpea, and White Clover

Concanavalin A: Lack of correlation between binding to rhizobium and specificity in the Rhizobium—legume symbiosis

Concanavalin A, a lectin from jackbean (Canavalia ensiformis), combined strongly with various nodulating and non-nodulating strains of Rhizobium regardless of their respective hosts. Thus, interactions between legume lectins and Rhizobium cells may not always account for the specificity expressed by the nodule bacteria for their respective legume hosts.

Effect of Seed Fumigation on the Symbiosis of Rhizobium sp. with Arachis hypogaea Linn

To minimize the loss due to insect pests during storage, the fumigation of the seeds is advocated. However, no information is available on the subject how these fumigants, if such fumigated seeds are treated with Rhizobium , will interact with the Rhizobium legume symbiosis. Hence, groundnut seeds treated with ethylene dibromide, ethylene dichloride carbon tetrachloride mixture (EDCT), chloropicrin, and phosphine were treated with Rhizobium and sown. Observations were made on the number, fresh weight and leghaemoglobin content of the nodules, and on the yield, dry weight and nitrogen content of the plants. The results indicated that all the four fumigants adversely affected the nodulation status and the yield of groundnut treated with Rhizobium , and hence the use of fumigated seeds for Rhizobium treatment is not advisable. The insecticide malathion is also used in store houses to protect groundnut seeds from insect pests. When the malathion-treated seeds were inoculated with Rhizobium and sown, no adverse effect on nodulation and yield was recorded. Die Begasung von Saatgut wird häufig als Mittel gegen Verluste durch Insekten angewendet. Es sind keine Angaben vorhanden, auf welche Art und Weise diese Begasung die Symbiose von Rhizobium mit der Pflanze beeinflußt. Darum wurde Erdnuß mit Athylenbromid, einem Äthylendichlorid-Kohlenstofftetrachlorid-Gemisch (EDCT), Chlorpikrin und Phosphin behandelt und angebaut. Die Zahl und die Masse der frischen Knöllchen, der Gehalt an Leghämoglobin der Knöllchen sowie Ertrag und Stickstoffgehalt der Pflanzen wurden ermittelt. Alle angewandten Mittel beeinflußten die Knöllchenbildung und den Ertrag nachteilig. Es ist daher nicht empfehlenswert, sie anzuwenden. Dagegen hatte das Insektizid Melathion keine Nachwirkung, wenn es während der Lagerung des Saatgutes angewandt wurde.

Genetics of symbiosis and nitrogen fixation in legumes.

Soon after the isolation of nodule bacteria in 1888, differences were recognized in the ability of bacterial strains to form nodules on particular host plants and in the nitrogen-fixing ability of the nodules so formed. These and other symbiotic heterogeneities were attributed, sometimes correctly, to bacterial strain differences, not then thought to be open to formal genetic analysis. The realization that the host plant was an essential component of this variability came only gradually, stimulated by observations of host varietal differences and by the demand for reliable and homogeneous material for experimental work. Only within the last two decades has host variability been studied by plant breeding, and bacterial strain differences by some of the methods of microbial genetics. This review, except for a brief reference to earlier work of some historic interest, will consider only genetic problems open to investigation by these methods. The developmental sequence in all legume nodules is broadly similar. The initial infection phases are followed by the induction of the nodule, the invasion of part of the nodular tissue and culminate in bacteroid formation and nitrogen fixation; the genetics of symbiosis will be considered in this context.

Techniques for studying physiological rhythms in legume symbiosis

Techniques for studying physiological rhythms in legume symbiosis

Temperature Characteristics of Bacterial Variation in Legume Symbiosis

Temperature Characteristics of Bacterial Variation in Legume Symbiosis