Denitrification in lucerne nodules and bacteroids supplied with nitrate

Arrese‐Igor, Cesar; Royuela, M.; Tejo, Pedro María Aparicio

doi:10.1111/j.1399-3054.1992.tb04701.x

Cited by 15 publications

(4 citation statements)

References 35 publications

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“…However, they do not in themselves prove that nitrate does not reach and exert some influence (other than a change in Lb) in the nodule central zone. Denitrification by bacteroids has been reported in alfalfa nodules after 3 d of exposure to 10 mM nitrate, implying nitrate entry into the central zone by that time (Arrese-Igor et al, 1992). Although our results relieve Lb of direct responsibility for observed changes in P, , they do not exclude indirect involvement of Lb, e.g.…”

Section: Mechanism Of Nitrate Lnhibitioncontrasting

confidence: 66%

Nitrate Effects on Nodule Oxygen Permeability and Leghemoglobin (Nodule Oximetry and Computer Modeling)

Denison

Harter

1995

Plant Physiol.

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Two current hypotheses to explain nitrate inhibition of nodule function both involve decreased O, supply for respiration in support of N, fixation. This decrease could result from either (a) decreased O, permeability (P,) of the nodule cortex, or (b) conversion of leghemoglobin (Lb) to an inactive, nitrosyl form. These hypotheses were tested using alfalfa (Medicago sativa L. cv WeevIchek) and birdsfoot trefoil (Lotus corniculatus L. cv Fergus) plants grown in growth pouches under controlled conditions. Nodulated roots were exposed to 1 O mM KNO, or Nitrate exposure can inhibit both nodulation of legumes and N, fixation by existing nodules (Streeter, 1988). Modification of the response of crop and forage legumes to nitrate may be desirable in some agricultura1 contexts, e.g. to increase the nitrogen contribution from a green manure crop or to decrease total nitrogen supply where nitrate leaching is a problem. The mechanism by which nitrate inhibits the activity of existing nodules has been controversial, despite considerable research on the topic.Early hypotheses involving a direct carbohydrate limitation of nodule metabolism or a direct nitrite toxicity are no longer widely accepted (Streeter, 1988;Vessey and Waterer, 1992). Instead, recent reviews summarize the evidence that nitrate inhibition of N, fixation involves a decreased O, supply for respiration in the nodule central zone (Vessey and Waterer, 1992;Hunt and Layzell, 1993). This evidence includes decreased FOL in nitrate-treated nodules (Layzell et al., 1990) and partia1 alleviation of nitrate inhibition by elevated external O, (Vessey et al., 1988). A decrease in FOL is not predicted by the direct carbohydrate limitation or nitrite toxicity hypotheses. In fact, inhibition of respiration by carbohydrate limitation or nitrite toxicity would be expected to decrease the capacity to consume O, diffusing into the nodule, thereby increasing central zone O, concentration and FOL.Decreased nodule O, permeability has been implicated in legume responses to several forms of stress (Hunt and Layzell, 1993). Past estimates of P, in nitrate-treated nodules were based on attempts to calculate the O, flux into nodules from net CO, exchange rates of nodulated roots. Although several variations on this approach (Schuller et al., 1988;Vessey et al., 1988;Minchin et al., 1992) a11 appeared to show a decrease in P, with nitrate exposure, a reexamination of nitrate effects by an independent method seemed worthwhile. Therefore, in this paper we report nitrate effects on P, in alfalfa (Medicago sativa) and birdsfoot trefoil (Lotus corniculatus) as measured by nodule oximetry (Denison and Layzell, 1991). This method estimates P, of intact, attached nodules by spectrophotometric monitoring of changes in FOL in response to changes in external O, concentration.Nodule O, permeability is defined here explicitly by Fick's law of diffusionwhere F is the total inward O, flux (mol/s) across the gas diffusion barrier in the nodule cortex (Tjepkema and Yocum, 1973), P , is the O, perm...

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Section: Mechanism Of Nitrate Lnhibitioncontrasting

confidence: 66%

Nitrate Effects on Nodule Oxygen Permeability and Leghemoglobin (Nodule Oximetry and Computer Modeling)

Denison

Harter

1995

Plant Physiol.

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“…(c) Rhizobia fitness (reproductives per nodule and polyhydroxybutyrate per reproductive) assessment Nodules were harvested and rinsed with sterile deionized water three times before being crushed in ascorbic acid buffer [27]. There was no surface sterilization performed on the nodules since this had previously led to some rhizobial death, as evidenced by low colony counts relative to flow cytometric counts.…”

Section: Methodsmentioning

confidence: 99%

Failure to fix nitrogen by non-reproductive symbiotic rhizobia triggers host sanctions that reduce fitness of their reproductive clonemates

2011

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The legume -rhizobia symbiosis is a classical mutualism where fixed carbon and nitrogen are exchanged between the species. Nonetheless, the plant carbon that fuels nitrogen (N 2 ) fixation could be diverted to rhizobial reproduction by 'cheaters'-rhizobial strains that fix less N 2 but potentially gain the benefit of fixation by other rhizobia. Host sanctions can decrease the relative fitness of less-beneficial reproductive bacteroids and prevent cheaters from breaking down the mutualism. However, in certain legume species, only undifferentiated rhizobia reproduce, while only terminally differentiated rhizobial bacteroids fix nitrogen. Sanctions were, therefore, tested in two legume species that host non-reproductive bacteroids. We demonstrate that even legume species that host non-reproductive bacteroids, specifically pea and alfalfa, can severely sanction undifferentiated rhizobia when bacteroids within the same nodule fail to fix N 2 . Hence, host sanctions by a diverse set of legumes play a role in maintaining N 2 fixation.

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“…Other nodules were harvested from plants grown in the growth chamber and were never dried. Rehydrated or fresh nodules were crushed in ascorbic acid buffer (Arrese‐Igor et al. , 1992) and centrifuged at 100 g for 10 min to separate rhizobia from plant material.…”

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confidence: 99%

Multiple evolutionary origins of legume traits leading to extreme rhizobial differentiation

et al. 2010

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Summary When rhizobia differentiate inside legume host nodules to become nitrogen‐fixing bacteroids, they undergo a physiological as well as a morphological transformation. These transformations are more extreme in some legume species than others, leading to fundamental differences in rhizobial life history and evolution. Here, we analysed the distribution of different bacteroid morphologies over a legume phylogeny to understand the evolutionary history of this host‐influenced differentiation. Using existing electron micrographs and new flow cytometric analyses, bacteroid morphologies were categorized as swollen or nonswollen for 40 legume species in the subfamily Papilionoideae. Maximum likelihood and Bayesian frameworks were used to reconstruct ancestral states at the bases of all major subclades within the papilionoids. Extreme bacteroid differentiation leading to swelling was found in five out of the six major papilionoid subclades. The inferred ancestral state for the Papilionoideae was hosting nonswollen bacteroids, indicating at least five independent origins of host traits leading to swollen bacteroids. Repeated evolution of host traits causing bacteroid swelling indicates a possible fitness benefit to the plant. Furthermore, as bacteroid swelling is often correlated with loss of reproductive viability, the evolution of bacteroid cooperation or cheating strategies could be fundamentally different between the two bacteroid morphologies.

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Denitrification in lucerne nodules and bacteroids supplied with nitrate

Cited by 15 publications

References 35 publications

Nitrate Effects on Nodule Oxygen Permeability and Leghemoglobin (Nodule Oximetry and Computer Modeling)

Nitrate Effects on Nodule Oxygen Permeability and Leghemoglobin (Nodule Oximetry and Computer Modeling)

Failure to fix nitrogen by non-reproductive symbiotic rhizobia triggers host sanctions that reduce fitness of their reproductive clonemates

Multiple evolutionary origins of legume traits leading to extreme rhizobial differentiation

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