Suppression of nodulation in soybeans by superoptimal inoculation with <i>Bradyrhizobium japonicum</i>

Takats, Stephen T.

doi:10.1111/j.1399-3054.1986.tb05597.x

Cited by 13 publications

(14 citation statements)

References 15 publications

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“…This region is the first one inoculated in double inoculation protocols. The number of nodules which appeared in this region was greatly reduced when a large second inoculum was given 10 h after the first inoculum (22). This result was not 865 observed by Pierce and Bauer (18), whose protocol for double inoculation was different.…”

supporting

confidence: 47%

“…The fact that they agree suggests that the failure to obtain a second nodulation peak (9,18) was due simply to concentration of bacteria used in the second inoculum. Soybean roots clearly show a reduction of nodule yield in response to large inoculum doses of B. japonicum (18,22). Thus, it is not anomolous to find that a large second inoculum delivered to the root shortly after the first inoculum will reduce nodule yield; the only peculiarity is that the effect is localized basally in the root.…”

Section: Discussionmentioning

confidence: 92%

“…Procedures for growing soybean seedlings (Glycine max L. Merrill cv Pride 216) as well as for culturing Bradyrhizobium japonicum 110 followed those already described (22). In most experiments, B. japonicum 110 spc 4+ (13) was used instead of the B. japonicum 110 ARS+ used previously, since it was the parent strain used to construct Nod-mutants (13) and served as an isogenic Nod' control.…”

Section: Methodsmentioning

confidence: 99%

“…Double inoculation experiments were carried out with a 17-h interval between the first and second inoculations, instead of the 10-h interval used previously (22). This was only 2 h longer than the interval used by Pierce and Bauer (18) and should have resulted in the same suppression of apical nodulation that they obtained if optimization of the size of the first inoculum was the only factor determining the autoregulatory response.…”

Section: Nodulation After Longer Delay Between Double Inoculationsmentioning

confidence: 99%

“…The present investigation was undertaken to determine the basis for the observation (22) that very early feedback regulation appears to control the nodulation not in the apical region but instead in the basal region of the root, which is initially most susceptible to infection by the bacteria (1,2). This region is the first one inoculated in double inoculation protocols.…”

mentioning

confidence: 99%

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Early Autoregulation of Symbiotic Root Nodulation in Soybeans

Takats

1990

Plant Physiol.

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Autoregulation of symbiotic root nodulation in soybean seedlings (Glycine max L. Merrill cv Pride 216) was studied following double inoculation of primary roots with Bradyrhizobium japonicum 110. When the second inoculation was given 10 or 17 hours after the first, the nodulation in the first-inoculated region of the root was suppressed. The effect was eliminated if B. japonicum 110 containing Tn5 insertions in the 'common' nod ABC genes was used for the second inoculation, indicating the requirement for changes in the root mediated by these bacterial genes. When the root cortex in the suppressed basal region was examined 3 days after inoculation, cell division centers were present in numbers not significantly different from the numbers in contrQl roots given a sham second inoculation; their size distribution, however, showed a failure of enlargement compared with controls.Feedback suppression of symbiotic root nodulation ('autoregulation') was discovered in 1952 by Nutman in red clover ( 16) and has since been demonstrated in several other legume plants (see 19 for review). Nutman interpreted it as an inhibition of new nodule production by already established nodules on the root, because surgical excision of established nodules or nodule meristems allowed additional nodulation (16). Split-root techniques have since been used (12) to demonstrate the systemic nature of the response in soybean plants (Glycine max L. Merrill). Grafting experiments with soybeans have shown that feedback suppression requires the normal shoot, since the response is lost when a mutant shoot which lacks the normal nodulation control ('supernodulating') is substituted for the normal one (8,17).Double inoculation experiments carried out by Pierce and Bauer (18) showed that feedback suppression was actually a plant response which could not be explained by limitation of the number of infective bacteria. Their experiments demonstrated that a second inoculation 15 h after the first produced virtually no nodules, provided that the bacterial concentration in the first inoculum was optimized for nodule yield.The present investigation was undertaken to determine the basis for the observation (22) that very early feedback regulation appears to control the nodulation not in the apical region but instead in the basal region of the root, which is initially most susceptible to infection by the bacteria (1, 2). This region is the first one inoculated in double inoculation protocols. The number of nodules which appeared in this region was greatly reduced when a large second inoculum was given 10 h after the first inoculum (22). This result was not 865 observed by Pierce and Bauer (18), whose protocol for double inoculation was different. Two questions were therefore asked: (a) Did the effect require the 'common' nod genes in B. japonicum which are responsible for nodulation? If so, it would indicate that the effect depended on specific gene expression and was not due to nonspecific phenomena incidental to the double inoculation protocol, e.g. di...

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supporting

confidence: 47%

Section: Discussionmentioning

confidence: 92%

Section: Methodsmentioning

confidence: 99%

Section: Nodulation After Longer Delay Between Double Inoculationsmentioning

confidence: 99%

mentioning

confidence: 99%

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Early Autoregulation of Symbiotic Root Nodulation in Soybeans

Takats

1990

Plant Physiol.

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Feedback regulation of nodule formation in alfalfa

Caetano‐Anollés

Bauer

1988

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When high dosages of wild-type Rhizobium meliloti RCR2011 were inoculated at two different times, 24 h apart, onto either the primary roots of alfalfa (Medicago sativa L.) seedlings or onto lateral roots on opposite sides of a split-root system, the number of nodules generated by the second inoculum was much smaller than the number generated by the first inoculum. These results provide evidence that alfalfa has an active, systemic mechanism for feedback control of nodulation. Non-nodulating mutants and delayed, weakly nodulating mutants did not elicit a discernable suppression of nodulation by subsequently inoculated wild-type cells. An appreciable number of Rhizobium infections thus seem required to elicit the suppressive response. Mutants in nodulation regions IIb and IIa nodulated extensively in the initially susceptible region of the root, but nodule initiation by these mutants was 100-1000 times less efficient, respectively, than the parent. Nodules formed by these mutants emerged 1 d later than normal. The IIb mutants elicited a relatively strong suppression of nodulation in younger parts of the root, but region-IIa mutants elicited only a weak response. These results indicate that elicitation of the regulatory response need not be proportional to nodule formation and imply that genes in region IIa play an important role in elicitation. At high dosages, the region-II mutants induced the development of thick, short roots in a considerably higher percentage of plants than the wild-type bacteria. Nodules generated by wild-type isolates and region-II mutants did not emerge in strict acropetal sequence, probably because some infections developed more slowly than others. Prior exposure of the root to non-nodulating mutants resulted in nodulation by the parent in regions of the root otherwise too mature to be susceptible, indicating that exposure to these mutants may affect the sequence of root development.

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Enhanced nodule initiation on alfalfa by wild-typeRhizobium meliloti co-inoculated withnod gene mutants and other bacteria

Caetano‐Anollés

Bauer

1988

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Nodule formation on alfalfa (Medicago sativa L.) roots was determined at different inoculum dosages for wild-typeRhizobium meliloti strain RCR2011 and for various mutant derivatives with altered nodulation behavior. The number of nodules formed on the whole length of the primary roots was essentially constant regardless of initial inoculum dosage or subsequent bacterial multiplication, indicative of homeostatic regulation of total nodule number. In contrast, the number of nodules formed in just the initially susceptible region of these roots was sigmoidally dependent on the number of wild-type bacteria added, increasing rapidly at dosages above 5·10(3) bacteria/plant. This behavior indicates the possible existence of a threshold barrier to nodule initiation in the host which the bacteria must overcome. When low dosages of the parent (10(3) cells/plant) were co-inoculated with 10(6) cells/plant of mutants lacking functionalnodA, nodC, nodE, nodF ornodH genes, nodule initiation was increased 10- to 30-fold. Analysis of nodule occupancy indicated that these mutants were able to help the parent (wild-type) strain initiate nodules without themselves occupying the nodules. Co-inoculation withR. trifolii orAgrobacterium tumefaciens cured of its Ti plasmid also markedly stimulated nodule initiation by theR. meliloti parent strain. Introduction of a segment of the symbiotic megaplasmid fromR. meliloti intoA. tumefaciens abolished this stimulation.Bradyrhizobium japonicum and a chromosomal Tn5 nod(-) mutant ofR. meliloti did not significantly stimulate nodule initiation when co-inoculated with wild-typeR. meliloti. These results indicate that certainnod gene mutants and members of theRhizobiaceae may produce extracellular "signals" that supplement the ability of wild-typeR. meliloti cells to induce crucial responses in the host.

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Suppression of nodulation in soybeans by superoptimal inoculation with Bradyrhizobium japonicum

Cited by 13 publications

References 15 publications

Early Autoregulation of Symbiotic Root Nodulation in Soybeans

Early Autoregulation of Symbiotic Root Nodulation in Soybeans

Feedback regulation of nodule formation in alfalfa

Enhanced nodule initiation on alfalfa by wild-typeRhizobium meliloti co-inoculated withnod gene mutants and other bacteria

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