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Auxin and nitric oxide control indeterminate nodule formation.

Pii Y, Crimi M, Cremonese G, Spena A, Pandolfini T - BMC Plant Biol. (2007)

Bottom Line: IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules.Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia.The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dipartimento Scientifico Tecnologico, University of Verona, Verona, Italy. pii@sci.univr.it

ABSTRACT

Background: Rhizobia symbionts elicit root nodule formation in leguminous plants. Nodule development requires local accumulation of auxin. Both plants and rhizobia synthesise auxin. We have addressed the effects of bacterial auxin (IAA) on nodulation by using Sinorhizobium meliloti and Rhizobium leguminosarum bacteria genetically engineered for increased auxin synthesis.

Results: IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules. Indeterminate legumes (Medicago species) bearing IAA-overproducing nodules showed an enhanced lateral root development, a process known to be regulated by both IAA and nitric oxide (NO). Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia. The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.

Conclusion: The data hereby presented demonstrate that auxin synthesised by rhizobia and nitric oxide positively affect indeterminate nodule formation and, together with the observation of increased expression of an auxin efflux carrier in roots bearing nodules with higher IAA and NO content, support a model of nodule formation that involves auxin transport regulation and NO synthesis.

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Effects of the NO scavenger cPTIO on nodulation. Nodule number of Medicago truncatula plants inoculated by IAA and control strain and treated with 1 mM cPTIO. Results are means ± SE (n = at least 12). cPTIO treatments are significantly different from respective controls, (P < 0.05). IAA: nodules produced by the S. meliloti IAA strain. Control: nodules produced by the S. meliloti control strain.
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Figure 7: Effects of the NO scavenger cPTIO on nodulation. Nodule number of Medicago truncatula plants inoculated by IAA and control strain and treated with 1 mM cPTIO. Results are means ± SE (n = at least 12). cPTIO treatments are significantly different from respective controls, (P < 0.05). IAA: nodules produced by the S. meliloti IAA strain. Control: nodules produced by the S. meliloti control strain.

Mentions: In order to assess a possible link between NO and indeterminate nodule formation, we tested the effect of the NO scavenger, cPTIO on M. truncatula plants inoculated by IAA and control S. meliloti strains. The plants, grown in plastic tubes on perlite supplemented with N-free nutrient solution, were treated with 1 mM cPTIO 2, 24 and 48 h after rhizobia inoculation. NO depletion by treatment with cPTIO caused a significant reduction in nodule number (Fig. 7) in plants inoculated with either IAA-overproducing or control rhizobia. This finding demonstrates that NO depletion inhibited indeterminate nodule formation and completely abolished the auxin stimulatory effect on nodulation. Nitric oxide depletion inhibited the increase in lateral root growth caused by IAA-overproducing strain (data not shown), confirming previous data on the role played by NO in lateral root formation in tomato [14]. Primary root length and shoot growth were not affected by 1 mM cPTIO. Furthermore, the treatment with cPTIO has no effect on S. meliloti growth (see additional file 4).


Auxin and nitric oxide control indeterminate nodule formation.

Pii Y, Crimi M, Cremonese G, Spena A, Pandolfini T - BMC Plant Biol. (2007)

Effects of the NO scavenger cPTIO on nodulation. Nodule number of Medicago truncatula plants inoculated by IAA and control strain and treated with 1 mM cPTIO. Results are means ± SE (n = at least 12). cPTIO treatments are significantly different from respective controls, (P < 0.05). IAA: nodules produced by the S. meliloti IAA strain. Control: nodules produced by the S. meliloti control strain.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1878477&req=5

Figure 7: Effects of the NO scavenger cPTIO on nodulation. Nodule number of Medicago truncatula plants inoculated by IAA and control strain and treated with 1 mM cPTIO. Results are means ± SE (n = at least 12). cPTIO treatments are significantly different from respective controls, (P < 0.05). IAA: nodules produced by the S. meliloti IAA strain. Control: nodules produced by the S. meliloti control strain.
Mentions: In order to assess a possible link between NO and indeterminate nodule formation, we tested the effect of the NO scavenger, cPTIO on M. truncatula plants inoculated by IAA and control S. meliloti strains. The plants, grown in plastic tubes on perlite supplemented with N-free nutrient solution, were treated with 1 mM cPTIO 2, 24 and 48 h after rhizobia inoculation. NO depletion by treatment with cPTIO caused a significant reduction in nodule number (Fig. 7) in plants inoculated with either IAA-overproducing or control rhizobia. This finding demonstrates that NO depletion inhibited indeterminate nodule formation and completely abolished the auxin stimulatory effect on nodulation. Nitric oxide depletion inhibited the increase in lateral root growth caused by IAA-overproducing strain (data not shown), confirming previous data on the role played by NO in lateral root formation in tomato [14]. Primary root length and shoot growth were not affected by 1 mM cPTIO. Furthermore, the treatment with cPTIO has no effect on S. meliloti growth (see additional file 4).

Bottom Line: IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules.Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia.The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.

View Article: PubMed Central - HTML - PubMed

Affiliation: Dipartimento Scientifico Tecnologico, University of Verona, Verona, Italy. pii@sci.univr.it

ABSTRACT

Background: Rhizobia symbionts elicit root nodule formation in leguminous plants. Nodule development requires local accumulation of auxin. Both plants and rhizobia synthesise auxin. We have addressed the effects of bacterial auxin (IAA) on nodulation by using Sinorhizobium meliloti and Rhizobium leguminosarum bacteria genetically engineered for increased auxin synthesis.

Results: IAA-overproducing S. meliloti increased nodulation in Medicago species, whilst the increased auxin synthesis of R. leguminosarum had no effect on nodulation in Phaseolus vulgaris, a legume bearing determinate nodules. Indeterminate legumes (Medicago species) bearing IAA-overproducing nodules showed an enhanced lateral root development, a process known to be regulated by both IAA and nitric oxide (NO). Higher NO levels were detected in indeterminate nodules of Medicago plants formed by the IAA-overproducing rhizobia. The specific NO scavenger cPTIO markedly reduced nodulation induced by wild type and IAA-overproducing strains.

Conclusion: The data hereby presented demonstrate that auxin synthesised by rhizobia and nitric oxide positively affect indeterminate nodule formation and, together with the observation of increased expression of an auxin efflux carrier in roots bearing nodules with higher IAA and NO content, support a model of nodule formation that involves auxin transport regulation and NO synthesis.

Show MeSH
Related in: MedlinePlus