Assimilation of 15NO3− Taken Up by Plants in the Light and in the Dark

Rufty, Thomas W.; Israel, Daniel W.; Volk, Richard J.

doi:10.1104/pp.76.3.769

Cited by 44 publications

(22 citation statements)

References 25 publications

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“…Two specific effects were apparent: (a) total uptake was 38% less in the dark (236 versus 380 Mmol plant-'), and (b) a smaller percentage of the NO3-taken up in darkness was reduced (30% versus 75%). As was noted in a previous experiment (28), most of the '5NO3-present in the plant at the end of the dark period (83%) was located in the root system.…”

Section: Resultssupporting

confidence: 79%

Endogenous NO₃⁻ in the Root as a Source of Substrate for Reduction in the Light

Rufty¹,

Volk²,

MacKown³

1987

Plant Physiol.

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ABSTRACIAn experiment was conducted to investigate the reduction of endogenOUS No3-, which had been taken up by plants in darkness, during the course of the subsequent light period. Vegetative, nonnodulated soybean plants (Glycine max [L]. Merrill, 'Ransom') were exposed to 1.0 millimolar I5N03-for 12 hours in darkness and then returned to a solution containing 1.0 millimolar 4NO3-for the 12 hours 'chase' period in the light. Another set of plants was exposed to 'I5NO3-during the light period to allow a direct comparison of contributions of substrate from the endogenous and exogenous sources. At the end of the I5NO3-exposure in the dark, 70% of the absorbed 15NO3-remained unreduced, and 83% of this unreduced NO3-was retained in roots. The pool of endogenous '5NO3-in roots was depleted at a steady rate during the initial 9 hours of light and was utilized almost exclusively in the formation of insoluble reduced-N in leaves. Unlabeled endogenous NO3-, which had accumulated in the root prior to the previous dark period, also was depleted in the light. When exogenous 15NO3-was supplied during the light period, the rate of assimilation progressively increased, reflecting an increased rate of uptake and decreased accumulation of NO3-in the root tissue. The dark-absorbed endogenous NO3-in the root was the primary source of substrate for whole-plant NO3-reduction in the first 6 hours of the light period, and exogenous N03-was the primary source of substrate thereafter. It is concluded that retention of NO3-in roots in darkness and its release in the following light period is an important whole-plant regulatory mechanism which serves to coordinate delivery of substrate with the maximal potential for NO3-assimilation in photosynthetic tissues. (14). The atom % 'sN of the NO3-fraction was determined by mass spectrometry using a nitric oxide procedure (34). The analysis of reduced N involved an initial removal of NO3-(20), followed by Kjeldahl digestion (17) and colorimetric determination of NH4' (2). The NH4' in the remaining digest was recovered by diffusion and the atom % '5N determined mass spectrometrically using a freeze-layer procedure (33).The tissue samples were analyzed for NO3-and soluble and insoluble reduced nitrogen. After being freeze-dried, weighed and ground, the tissue was extracted with methanol:chloroform:water (13:4:3). Following separation of the chloroform from the methanol:water fraction, the chloroform was added back to the tissue residue, with this constituting the insoluble reduced N fraction. Total nitrogen -and 'IN in the insoluble reduced N fraction were determined as described for exudate reduced N, omitting the NO3-removal procedure. The methanol:water fraction was analyzed for NO3-and soluble reduced N. After the methanol was evaporated, an aliquot was taken and NO3-and its '5N enrichment were determined as in the exudate analysis. Nitrate in the remainder of the sample was removed and the soluble reduced N and atom % '5N determined as in the analysis of exudate reduced N. All tissue "5N d...

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Section: Resultssupporting

confidence: 79%

Endogenous NO₃⁻ in the Root as a Source of Substrate for Reduction in the Light

Rufty¹,

Volk²,

MacKown³

1987

Plant Physiol.

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“…The results (not shown) were similar to those shown in Figure 4 and inhibitory concentrations of KNO3 stimulated proton influx before causing the ApH to collapse. It has been reported that NO3-is stored in the vacuoles of barley roots during the night and released to the shoots during the day (29). Release of NO3-from the vacuole by a regulated symport is an attractive hypothesis.…”

Section: Discussionmentioning

confidence: 99%

“…The effect of NO3 on the tonoplast ATPase in vivo also needs to be elucidated. The physiological significance of the N03 -inhibition is unclear and puzzling, because the vacuole stores nitrate (23,29). Nitrate inhibits the mitochondrial F,F0-ATPase and the tonoplast H+-ATPase with a Ki of only 5 to 10 mm (27,31) although it was estimated that the cytoplasmic concentration of nitrate was approximately 4 mM and the vacuolar concentration was greater than 40 mm for barley leaf protoplasts (23).…”

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confidence: 99%

Variable Effects of Nitrate on ATP-Dependent Proton Transport by Barley Root Membranes

DuPont

1987

Plant Physiol.

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ABSTRACITThe effects of NO3-and assay temperature on proton translocating ATPases in membranes of barley (Hordeum vulgare L. cv California Mariout 72) roots were examined. The membranes were fractionated on continuous and discontinuous sucrose gradients and proton transport was assayed by monitoring the fluorescence of acridine orange. A peak of H+-ATPase at 1.11 grams per cubic centimeter was inhibited by 50 millimolar KN03 when assayed at 24°C or above and was tentatively identified as the tonoplast H+-ATPase. A smaller peak of H+-ATPase at 1.16 grams per cubic centimeter, which was not inhibited by KN03 and was partially inhibited by vanadate, was tentatively identified as the plasma membrane H'-ATPase. A step gradient gave three fractions enriched, respectively, in endoplasmic reticulum, tonoplast ATPase, and plasma membrane ATPase. There was a delay before 50 millimolar KNO3 inhibited ATP hydrolysis by the tonoplast ATPase at 12°C and the initial rate of proton transport was stimulated by 50 millimolar KNO3. The time course for fluorescence quench indicated that addition of ATP in the presence of KN03 caused a pH gradient to form that subsequently collapsed. This biphasic time course for proton transport in the presence of KN03 was explained by the temperature-dependent delay of the inhibition by KNO3. The plasma membrane H'-ATPase maintained a pH gradient in the presence of KN03 for up to 30 minutes at 24°C.The characteristic that is used most frequently to identify the tonoplast ATPase is that the enzyme is inhibited by NO3-but not by vanadate or azide (3, 5, 9, 19-21, 24, 26, 31). Other inhibitors ofthe tonoplast ATPase, such as DCCD, are less useful, because they affect all of the proton-translocating ATPases (31).However, the effects of NO3-on the tonoplast H+-ATPase are complex (4, 18) and NO3-inhibits other ATPases as well. For example, a putative Golgi membrane H+-ATPase was partially inhibited by N03 (7) and the mitochondrial F,F0-ATPase was inhibited by NO3- (27,31). It is important to clarify the effects of nitrate on the tonoplast ATPase for several reasons. The criteria for using NO3-to identify the tonoplast ATPase need to be defined, particularly since there is some confusion in the literature between the effects of NO3-as an inhibitor of the ATPase and as a substrate for a NO3-/H' symport (4). The effect of NO3 on the tonoplast ATPase in vivo also needs to be elucidated. The physiological significance of the N03 -inhibition is unclear and puzzling, because the vacuole stores nitrate (23,29). Nitrate inhibits the mitochondrial F,F0-ATPase and the tonoplast H+-ATPase with a Ki of only 5 to 10 mm (27,31) although it was estimated that the cytoplasmic concentration of nitrate was approximately 4 mM and the vacuolar concentration was greater than 40 mm for barley leaf protoplasts (23).Barley roots have been used extensively for studies of ion transport and nitrogen metabolism, but until recently it has been difficult to obtain membrane preparations from barley that are suitable for studies of ion...

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“…Ion movement across the cell membrane is highly sensitive to changes in soil or root temperature (Chapin, 1974 ;BassiriRad et al, 1993), oxygen concentration of the rooting medium (Epstein, 1972), metabolic inhibitors , and light and\or carbohydrate availability (Rufty et al, 1984 ;Glass, 1989 ;Raper et al, 1991), which strongly suggest the presence of an energy-dependent uptake system. Despite the early recognition by Van den Honert (see Glass, 1989) that root ion uptake is an active process, a clear mechanism of uptake was not put forward until Epstein & Hagen (1952) introduced the concept of membrane-bound transporters or carriers.…”

Section: Root Uptake Kinetics : the Transporter Concept And Definitionsmentioning

confidence: 99%

Kinetics of nutrient uptake by roots: responses to global change

2000

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There is a growing recognition that accurate predictions of plant and ecosystem responses to global change require a better understanding of the mechanisms that control acquisition of growth-limiting resources. One such key mechanism is root physiological capacity to acquire nutrients. Changes in kinetics of root nitrogen (N) uptake might influence the extent to which terrestrial ecosystems will be able to sequester excesses in carbon (C) and N loads. Despite its significant role in determining plant and ecosystem cycling of C and N, there is little information on whether, or how, root nutrient uptake responds to global change. In this review various components of global change, namely increased CO # concentration, increased soil temperature and increased atmospheric N deposition and their effects on kinetics of root nutrient uptake are examined. The response of root nutrient uptake kinetics to high CO # is highly variable. Most of this variability might be attributable to differences in experimental protocols, but more recent evidence suggests that kinetic responses to high CO # are also species-specific. This raises the possibility that elevated CO # might alter community composition by shifting the competitive interaction of co-occurring species. Uptake of NH % + and NO $ − seem to be differentially sensitive to high CO # , which could influence ecosystem trajectory toward N saturation. Increased soil temperature might increase N and P uptake capacity to a greater extent in species from warm and fluctuating soil habitats than in species from cold and stable soil environments. The few available data also indicate that increased soil temperature elicits a differential effect on uptake of NH % + versus NO $ − . Root uptake kinetics are generally down-regulated in response to long-term exposure to atmospheric N deposition. The extent of this down-regulation might, however, vary among species, stages of succession, land-use history and plant demand. Nonetheless, it is suggested that root N uptake kinetics might be an accurate biological indicator of the ecosystem capacity to retain N. The results reviewed here clearly highlight the scanty nature of the literature in the area of root nutrient absorption responses to global change. It is also clear that effects of one component of global change on root nutrient absorption capacity might be counterbalanced by another. Therefore, the generalizations offered here must be viewed with caution and more effort should be directed to rigorously test these initial observations in future research.

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Assimilation of ¹⁵NO₃⁻ Taken Up by Plants in the Light and in the Dark

Cited by 44 publications

References 25 publications

Endogenous NO₃⁻ in the Root as a Source of Substrate for Reduction in the Light

Endogenous NO₃⁻ in the Root as a Source of Substrate for Reduction in the Light

Variable Effects of Nitrate on ATP-Dependent Proton Transport by Barley Root Membranes

Kinetics of nutrient uptake by roots: responses to global change

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Assimilation of 15NO3− Taken Up by Plants in the Light and in the Dark

Cited by 44 publications

References 25 publications

Endogenous NO3− in the Root as a Source of Substrate for Reduction in the Light

Endogenous NO3− in the Root as a Source of Substrate for Reduction in the Light

Variable Effects of Nitrate on ATP-Dependent Proton Transport by Barley Root Membranes

Kinetics of nutrient uptake by roots: responses to global change

Contact Info

Product

Resources

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Assimilation of ¹⁵NO₃⁻ Taken Up by Plants in the Light and in the Dark

Endogenous NO₃⁻ in the Root as a Source of Substrate for Reduction in the Light

Endogenous NO₃⁻ in the Root as a Source of Substrate for Reduction in the Light