Nitrogenase Activity and Oxygen Diffusion in Nodules of Soyabean cv. Bragg and a Supernodulating Mutant: Effects of Nitrate

Schuller, Kathryn A.; Minchin, F. R.; Gresshoff, P.M.

doi:10.1093/jxb/39.7.865

Cited by 73 publications

(48 citation statements)

References 16 publications

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“…To our knowledge, we show for the first time that similar declines in TNA are obtained by exposing nodules to an atmosphere containing N, at a rather low partial pressure (57% N,, v/v). Severa1 groups have speculated that the Ar-induced decline might be due to a feedback mechanism by which a reduction in the concentration of products of N, assimilation is sensed, and TNA is reduced accordingly (Schuller et al, 1988;Layzell and Hunt, 1990;Streeter, 1995). Our results for the first 30 min of treatment support this hypothesis.…”

Section: Short-term Response Of N Fixation To Treatmentssupporting

confidence: 75%

“…Weisz and Sinclair (1987) and Ribet and Drevon (1995) observed no appreciable decline in the TNA of soybean root systems grown hydroponically upon exposure to C,H,, a treatment known to cause a decline in the TNA (C,H,-induced decline) that is similar to the Ar-induced decline. Schuller et al (1988) and King and Layzell (1991) noted a transient increase in the TNA after the initial Ar-induced decline. King and Layzell (1991) observed that this increase in the TNA was not associated with an increase in the O, concentration in the infected zone.…”

Section: Short-term Response Of N Fixation To Treatmentsmentioning

confidence: 95%

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Nitrogenase Activity Is Affected by Reduced Partial Pressures of N2 and NO3- 1

1997

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Optimal use of legumes i n cropping systems requires a thorough understanding of the interaction between inorganic N nutrition and symbiotic N, fixation. Our objective was to test the hypothesis that increased NO,-uptake by alfalfa (Medicago sativa L.) would compensate for lower N, fixation caused by low partial pressure of N, . Root systems of hydroponically grown alfalfa at 2 mg 1-' NO,--NExposure to reduced partial pressures of N, reduced total nitrogenase activity (TNA, measured as H, production in 20% O, and 80% Ar) by 40% within less than 30 min, followed by a recovery period over the next 30 min to initial activity. Five hours after treatments began, the TNA of plants exposed to 7 and 2% N, was substantially higher than pretreatment activities, whereas the TNA of plants exposed either t o O or 80% N, did not differ from pretreatment values. The decline in TNA due to NO,-exposure over 4 d was not affected by reduced partial pressure of N,. During the 1st h the proportion of electrons used for the reduction of N, fel1 from 0.52 to 0.23 for plants exposed t o 7% N, , and to 0.09 for plants exposed to 2% N, , and remained unchanged for the rest of the experiment. Although the hypothesis that alfalfa compensated with increased NO,-uptake for lower N, fixation was not validated by our results, we unexpectedly demonstrated that the decline in TNA upon exposure to NO,-was independent of the N,-fixing efficiency (i.e. the amount of N, reduced by nitrogenase) of the symbiosis.

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Section: Short-term Response Of N Fixation To Treatmentssupporting

confidence: 75%

Section: Short-term Response Of N Fixation To Treatmentsmentioning

confidence: 95%

Nitrogenase Activity Is Affected by Reduced Partial Pressures of N2 and NO3- 1

1997

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“…The responses of nodules to such seemingly unrelated factors as drought, nitrate, and defoliation all apparently involve changes in the gas permeability of this barrier (8,10,14,17,23,24 Variable gas permeability of nodules might result from changes in (a) the number or size of gas-filled radial pores through the barrier, (b) the thickness of water plugs in radial pores, (c) the extent of flooding between layers of cells, or (d) flooding of airspaces in the central zone.…”

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

Mathematical Modeling of Oxygen Diffusion and Respiration in Legume Root Nodules

Denison¹

1992

Plant Physiol.

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The 02 permeability of legume root nodules is under physiological control; decreases in permeability are triggered by various forms of stress. Two linked mathematical models were used to explore several hypotheses concerning the physical nature of the variable diffusion barrier in nodules. Respiration and diffusion of dissolved 02 and oxygenated leghemoglobin were simulated for the nodule cortex and the nodule interior. Measured nodule permeabilities were shown to be inconsistent with the hypothesis that large numbers of air-filled pores penetrate the diffusion barrier. Changes in the affinity of leghemoglobin for 02 or in the rate of cytoplasmic streaming in diffusion barrier cells did not result in the large changes in 02 permeability reported for real nodules. The presence or absence, but not the thickness, of aqueous plugs in radial pores through the cortex was found to have a large effect on permeability. Flooding of intercellular spaces, either between layers of cells in the cortex or in the nodule interior, also caused large changes in simulated permeability. The unsteady-state 02 method for determining nodule permeability was tested using data generated by the model. The accuracy of the method was confirmed, provided that certain assumptions (full oxygenation of leghemoglobin under pure 02 and uniform conditions in the nodule interior) are met.A diffusion barrier in legume root nodules restricts 02 flux into the nodule and thereby protects nitrogenase from inactivation by 02 (21,22). The responses of nodules to such seemingly unrelated factors as drought, nitrate, and defoliation all apparently involve changes in the gas permeability of this barrier (8,10,14,17,23,24 Variable gas permeability of nodules might result from changes in (a) the number or size of gas-filled radial pores through the barrier, (b) the thickness of water plugs in radial pores, (c) the extent of flooding between layers of cells, or (d) flooding of airspaces in the central zone.Under the "open pore" and "variable plug thickness" hypotheses, changes in nodule gas permeability result from changes in radial intercellular pores through a layer of closely packed cells in the nodule cortex. The open pore hypothesis postulates a low-resistance pathway through radial air-filled pores. Because the diffusion coefficient of 02 in air is 1O4 times that in water, diffusion through even a small number of open pores could dominate total diffusion (which also includes diffusion through cells) across the barrier. The low solubility of 02 in water or cytoplasm further decreases the diffusion rate in cells relative to air. It has been suggested that changes in either the radius (19,25) or the number (1 1) of open pores could control permeability. Under the variable plug thickness hypothesis (1 1), each pore contains a plug of water, and permeability depends on the thickness of the plug.The "flooded cortex" and "flooded interior" hypotheses have not previously been formulated explicitly. The

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“…The gas permeability of legume nodules is of considerable current interest because nodule responses to drought, nitrate, and photosynthate supply all apparently involve changes in nodule 02 permeability (6,7,11,14,16,20,22). Similar permeability changes occur in response to acetylene exposure (12) or with increased or decreased external 02 concentration (23,27).…”

mentioning

confidence: 99%

Measurement of Legume Nodule Respiration and O₂ Permeability by Noninvasive Spectrophotometry of Leghemoglobin

Denison¹,

Layzell²

1991

Plant Physiol.

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Physiological regulation of nodule gas permeability has a central role in the response of legumes to such diverse factors as drought, defoliation, and soil nitrate. A new method for quantifying nodule respiration and 02 permeability, based on noninvasive spectrophotometry of leghemoglobin, was evaluated using intact, attached nodules of Lotus corniulatus. First permeability (6, 7, 11, 14, 16, 20, 22 (24) has not been seriously criticized, but the procedure is tedious, requiring chromatographic analysis of many gas samples for each permeability measurement.FOL,' determined by spectrophotometry in total darkness, has been used to estimate O0 in cut nodules (1), detached nodules (13), and nodules flattened during growth (9, 10). An improved, pulse-modulated method (11) allowed measurement of FOL in intact, attached nodules under ambient light. This method revealed that several treatments which inhibit nitrogen fixation also decrease 0,, under both laboratory (I 1) and field (6) conditions. It was concluded that lower Oi in inhibited nodules resulted from a decrease in nodule 02 permeability.The rate of increase of FOL, after switching the atmosphere around a nodule from nitrogen to oxygen, was greater for control nodules than for inhibited nodules. The rate ofchange of FOL represents a balance between 02 diffusion through the cortex and 02 consumption in the nodule interior. Therefore, it was suggested that a rapid increase in FOL could indicate relatively high 02 permeability (6,11

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Nitrogenase Activity and Oxygen Diffusion in Nodules of Soyabean cv. Bragg and a Supernodulating Mutant: Effects of Nitrate

Cited by 73 publications

References 16 publications

Nitrogenase Activity Is Affected by Reduced Partial Pressures of N2 and NO3- 1

Nitrogenase Activity Is Affected by Reduced Partial Pressures of N2 and NO3- 1

Mathematical Modeling of Oxygen Diffusion and Respiration in Legume Root Nodules

Measurement of Legume Nodule Respiration and O₂ Permeability by Noninvasive Spectrophotometry of Leghemoglobin

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Nitrogenase Activity and Oxygen Diffusion in Nodules of Soyabean cv. Bragg and a Supernodulating Mutant: Effects of Nitrate

Cited by 73 publications

References 16 publications

Nitrogenase Activity Is Affected by Reduced Partial Pressures of N2 and NO3- 1

Nitrogenase Activity Is Affected by Reduced Partial Pressures of N2 and NO3- 1

Mathematical Modeling of Oxygen Diffusion and Respiration in Legume Root Nodules

Measurement of Legume Nodule Respiration and O2 Permeability by Noninvasive Spectrophotometry of Leghemoglobin

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Measurement of Legume Nodule Respiration and O₂ Permeability by Noninvasive Spectrophotometry of Leghemoglobin