Nitrate fluxes in squash seedlings measured with<sup>13</sup>N

Wieneke, J.

doi:10.1080/01904169209364304

Cited by 18 publications

(9 citation statements)

References 34 publications

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“…The possibility that ambient ammonium enhanced nitrate efflux also seems improbable, because root nitrate concentrations declined during desuppression (Table 4). This conclusion is supported by current evidence from '''N-nitrate studies Wieneke, 1992), which indicate that nitrate efflux is not enhanced by ambient ammonium. Thus, the increase in inhibition with time probably resulted from the re-accumulation of specific negative effectors in response to the presence of ambient ammonium or from a changing sensitivity of the nitrate system to those effectors.…”

Section: Inhibition Of Nitrate Uptake By Ambient Ammonium During Desusupporting

confidence: 78%

Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium

Jackson

Volk

1995

New Phytologist

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SUMMARYHigher plants are commonly exposed to rapid changes in the amounts and proportions of ammonium ancTnTtrate in their root environment. Some of the potential consequences of such changes have been determined by examining the suppressive effects of growing maize {Zea mays L.) seedlings with a high concentration (3 mM) of nitrogen on the subsequent uptake of nitrogen from a more dilute (0-2 mM) solution. To document the interactive role of nitrate and ammonium supply in suppression, ratios of these ions in the growth solution were maintained at 3:0, 2:1, 1:2 and 0:3. Rates of nitrate and ammonium uptake were then measured during initial (O-I h) exposure to 0 2 mM KNO., or NH^NO,, and hourly during a subsequent 7 h period of adaptation to the dilute solutions.Maximal suppression of nitrate uptake occurred only when both nitrate and ammonium were present (2:1 and 1:2) during prior growth. Nitrate uptake rates increased two-to three-fold as the seedlings adapted to the dilute KNC).| solution, but the presence of ammonium with nitrate in the prior growth solution restricted the rate and extent of recovery from suppression. Recovery was further restricted when ambient ammonium was present during the adaptation period. Neither the magnitude of suppression nor the rate and extent of recovery was readily explained by (a) the proportion of nitrate and ammonium present during prior growth, (6) carbohydrate concentrations in root and shoot tissues, (c) concentrations of nitrate and ammonium in the root tissue, or [d) indirect effects of ammonium on potassium uptake.Total nitrate reduction by the entire plant in the 8 h adaptation period decreased as tbe proportion of ammonium in the prior growth solution increased. Ambient ammonium restricted nitrate reduction only in seedlings previously grown entirely with ammonium. Thus the effect of ambient ammonium on nitrate reduction by the whole plant differed substantially from that on nitrate uptake. Since nearly all the ammonium taken up by the roots was assimilated, as well as that generated by nitrate reduction, it appears that carbohydrate supply did not limit the observed uptake of ammonium and nitrate. The accumulation in roots of both nitrate and specific metabolites of ammonium serving as negative effectors could account for most of the observations.

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Section: Inhibition Of Nitrate Uptake By Ambient Ammonium During Desusupporting

confidence: 78%

Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium

Jackson

Volk

1995

New Phytologist

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“…1994), Ingemarsson et al (1987) showed that efflux is nil or negligible in Lemna, except at very low N03~ concentrations (below lOmmol m"^). Induction of net NO3" uptake resulted in to increased efflux rate, as shown by comparing the almost undetectable level measured in uninduced squash plants with the value of 11 % of influx recorded after a 8h induction period on lOOmmol m'^ NO3" (Wieneke 1992). A change of the ^O^ concentration in the uptake solution has a great effect on the efflux versus influx ratio, as demonstrated in pea and barley (Wieneke 1994).…”

Section: Cytoplasmic No3" Pool and No3" Fluxes And Their Responses Tmentioning

confidence: 80%

Nitrate fluxes in soybean seedling roots and their response to amino acids: an approach using ¹⁵N

Muller

Tillard

Touraine

1995

Plant Cell & Environment

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This study was undertaken to determine which of the two NO3− fluxes (influx or efflux) across plasma membranes of root cells is the target of those amino acids which have been shown to inhibit net NO3− uptake (Muller & Touraine 1992, Journal of Experimental Botany43, 617–623). Parallel experiments were performed to mea‐sure either the time course of 15NO3− release from roots of soybean seedlings previously labelled with this isotope into non‐labelled solution, or the time course of 15N accumulation from labelled 15NO3− solution in non‐labelled seedlings. Focusing on the fate of 15NO3− in the cytoplasmic compartment, a model is developed to describe the time courses of the accumulation and release of tracer across the plasma membranes of root cells. Both time courses can be described by the sum of an exponential plus a linear term. In our material, the linear part of the accumulation time course is obscured by the NO3− fluxes exiting the cytoplasm, and the curve thus appears to be quasilinear over several minutes. However, we show that the use of the net tracer accumulation rate during this time period as an estimate of NO3− influx does not provide accurate estimates of influx and efflux. By contrast, 15NO3− efflux analysis permits calculation of the unidirectional fluxes across plasma membranes of root cells and the kinetic parameters of the cytoplasmic NO3− pool. Under our experimental conditions, efflux accounted for 30 to 50% of influx, and the cytoplasmic NO3− content was found to be in the 70–400nmol g−1 fw range. Using this methodology, the effect of amino acid accumulation on unidirectional fluxes of nitrate was then examined. Pretreatments of the seedlings with an amino acid which has been shown to inhibit net NO3− uptake led to concomitant decreases in net accumulation rates of 15NO3− and of reduced 15N in roots and total 15N in cotyledons. NO3− influx was markedly inhibited by these treatments, while NO3− efflux remained essentially unaffected, or even decreased. It is concluded that the target of the regulation of NO3− uptake by phloemtranslocated amino acids is the influx system.

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“…It has been referred to as the IHATS for NO,-and has been demonstrated in numerous plant systems . So far, the existence of a saturable IHATS has been demonstrated in Arabidopsis (Doddema and Telkamp, 1979), barley (Rao and Rains, 1976;Bloom, 1985;Lee and Drew, 1986;Konesky et al, 1989;Siddiqi et al, 1990;Aslam et al, 19921, buckwheat (Paulsamy and Chrungoo, 1994), corn (van den Honert and Hooymans, 1955;Neyra and Hageman, 1976;Pace and McClure, 1986;Hole et al, 1990), rice (Youngdahl et al, 19821, ryegrass (Lycklama, 1963), wheat (Goyal and Huffaker, 1986;Botelia et al, 1994), sunflower (Aguera et al, 1990), and squash (Wieneke, 1992). The K, s reported for IHATS in these species range from 7 to 187 WM (Bloom, 1985;Aslam et al, 1992).…”

Section: Ihatsmentioning

confidence: 99%

Kinetics of NO3- Influx in Spruce

1995

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lnfluxes of ',NO3-across the root plasmalemma were measured in intact seedlings of Picea g h c a (Moench) Voss. Three kinetically distinci uptake systems for NO,-were identified. In seedlings not previously exposed to external NO,-, a single Michaelis-Menten-type constitutive high-affinity transport system (CHATS) operated in a 2.5 to 500 p~ range of external NO,- NO,-uptake in higher plants is well characterized on the kinetics leve1 (Clarkson, 1986). There is general agreement in the literature that the dependence of NO,-uptake on [NO,-], can be resolved into at least two kinetically distinct systems (Clarkson and Lüttge, 1991;Glass and Siddiqi, 1995). Most kinetic experiments on NO,-uptake have been performed in cereal species and have been based on measurements of chemical depletion rates of NO,-from nutrient solutions, i.e. the determination of NO,-net flux (Neyra and Hageman, 1976;Rao and Rains, 1976;Doddema and Telkamp, 1979;Breteler and Nissen, 1982;Pace and McClure, 1986;Warner and Huffaker, 1989;Aslam et al., 1992). Although kinetic inferences from net flux studies have to be approached with caution, studies using radiotracers to determine the unidirectional influx of NO,-into root tissue have confirmed a (biphasic) pattern for NO,-uptake (Siddiqi et al., 1990). In the majority of studies, NO,-uptake appeared to be mediated by a HATS, which operated in a Michaelis-Menten-type fashion at [NO,-], 5 1 mM, and by a LATS, which operated in a linear fashion at [NO,-], 2 1 mM. Only a few workers reported apparently different or more complex patterns (Doddema and Telkamp, 1979;Breteler and Nissen, 1982).The NO,-uptake system in higher plants is unusual in that it is subject to induction by external NO,-(Minotti et al., 1969; see also Kronzucker et al., 1995b, for refs) (Lee and Drew, 1986;Behl et al., 1988;Klobus et al., 1988;Siddiqi et al., , 1990Hole et al., 1990). Because of significant differences in K , (Lee and Drew, 1986;Warner and Huffaker, 1989;Aslam et al., 1992) and response to metabolic poisons (Jackson et al., 19731, CHATS was considered a genetically discrete system from the IHATS apparent in the induced state (Clarkson, 1986). In some plants, the CHATS and IHATS were found to operate concurrently in the induced state (Warner and Huffaker, 1989; Aslam et al., 19921, whereas in others this was not obvious (Siddiqi et al., 1990).In contrast to the large body of experimental work on cereal species, our knowledge of NO,-uptake kinetics in conifer species is rudimentary, in spite of the enormous ecological and economic importance of such species. Only a small number of NO,-depletion studies in conifers have been reported (Peuke and Tischner, 1991;Kamminga-van Wijk and Prins, 1993;Plassard et al., 1994) and have provided no conclusive results as to the identity of the transport systems or their operation at different states of induction. It is possible that the poor growth response of many conifers on soils with NO,-as the predominant source of nitrogen (Kronzucker et al., 1995a(Kronzucker et al., , ...

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Nitrate fluxes in squash seedlings measured with¹³N

Cited by 18 publications

References 34 publications

Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium

Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium

Nitrate fluxes in soybean seedling roots and their response to amino acids: an approach using ¹⁵N

Kinetics of NO3- Influx in Spruce

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Nitrate fluxes in squash seedlings measured with13N

Cited by 18 publications

References 34 publications

Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium

Attributes of the nitrogen uptake systems of maize (Zea mays L.): maximal suppression by exposure to both nitrate and ammonium

Nitrate fluxes in soybean seedling roots and their response to amino acids: an approach using 15N

Kinetics of NO3- Influx in Spruce

Contact Info

Product

Resources

About

Nitrate fluxes in squash seedlings measured with¹³N

Nitrate fluxes in soybean seedling roots and their response to amino acids: an approach using ¹⁵N