Nitrate Reductase Activity in Maize (<i>Zea mays</i> L.) Leaves

Shaner, Dale L.; Boyer, John S.

doi:10.1104/pp.58.4.505

Cited by 143 publications

(74 citation statements)

References 16 publications

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“…Plants that are well fertilized with nitrate will tend to show higher xylem and apoplastic pH (e.g. Mengel et al, 1994;Mü hling and Lauchli, 2001), but soil water deficit often reduces nitrate uptake and transport to shoots in the xylem (Shaner and Boyer, 1976;Fig. 12), an observation that is not consistent with a drought-induced increase in xylem pH.…”

Section: Discussionmentioning

confidence: 77%

“…Plants that are well supplied with nitrate will show higher xylem and apoplastic pH (Mengel et al, 1994;Mü hling and Lauchli, 2001). Soil water deficit generally reduces nitrate uptake and transport to shoots in the xylem (Shaner and Boyer, 1976), which should acidify sap, but this is not always the case as Goodger et al (2005) have shown that mild soil drying can increase xylem nitrate concentrations. In addition to this, Lips (1997) has proposed a shift in nitrate reduction from shoots to roots as soil dries, and this will potentially impact significantly on sap pH in droughted plants.…”

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confidence: 99%

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Modification of Leaf Apoplastic pH in Relation to Stomatal Sensitivity to Root-Sourced Abscisic Acid Signals

2006

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The confocal microscope was used to determine the pH of the leaf apoplast and the pH of microvolumes of xylem sap. We quantified variation in leaf apoplast and sap pH in relation to changes in edaphic and atmospheric conditions that impacted on stomatal sensitivity to a root-sourced abscisic acid signal. Several plant species showed significant changes in the pH of both xylem sap and the apoplast of the shoot in response to environmental perturbation. Xylem sap leaving the root was generally more acidic than sap in the midrib and the apoplast of the leaf. Increasing the transpiration rate of both intact plants and detached plant parts resulted in more acidic leaf apoplast pHs. Experiments with inhibitors suggested that protons are removed from xylem sap as it moves up the plant, thereby alkalinizing the sap. The more rapid the transpiration rate and the shorter the time that the sap resided in the xylem/apoplastic pathway, the smaller the impact of proton removal on sap pH. Sap pH of sunflower (Helianthus annuus) and Commelina communis did not change significantly as soil dried, while pH of tomato (Lycopersicon esculentum) sap increased as water availability in the soil declined. Increasing the availability of nitrate to roots also significantly alkalinized the xylem sap of tomato plants. This nitrogen treatment had the effect of enhancing the sensitivity of the stomatal response to soil drying. These responses were interpreted as an effect of nitrate addition on sap pH and closure of stomata via an abscisic acid-based mechanism.

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Section: Discussionmentioning

confidence: 77%

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confidence: 99%

Modification of Leaf Apoplastic pH in Relation to Stomatal Sensitivity to Root-Sourced Abscisic Acid Signals

2006

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“…There is some compensation for this impairment by the apparent greater induction of NRA in NaNO3 roots than in KNO roots. The maintenance of high NRA depends on a continuous N03 flux (1,19,20). The high NRA in NaNO3 roots is then the result of N03-absorption at a rate much faster than N03-translocation to leaves.…”

Section: Resultsmentioning

confidence: 99%

“…Blevins et al (4) showed that in roots of barley seedlings treated with Ca(NO3)2, N03-accumulation, organic acid accumulation, and NRA were much less than in KNO3-treated seedlings. Shaner and Boyer (19,20), by using NO3 depletion and cooling of roots and water stress, showed that the decrease in leaf NRA was due to decreased N03 flux to leaves. In wheat seedlings treated with NaNO3, N03-translocation and accumulation were low unless the seedlings had been given a pretreatment with K+ (8).…”

Section: Resultsmentioning

confidence: 99%

Role of Potassium and Malate in Nitrate Uptake and Translocation by Wheat Seedlings

Blevins¹,

Barnett²,

Frost³

1978

Plant Physiol.

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Wheat seedlings ( Tddcum vulgare) treated with 1 mM KNO3 or NaNO3, in the presence of 0.2 mM CaSO4, were compared during a 48-hour period with respect to nitrate uptake, translocatlon, accumulation and reduction; cation uptake and accumulation; and malate accumulation. Seedlngs treated with KNO3 absord and accumulated more nitrate, had higher nitrate reductase levels in leaves but less in roots, accumulated 17 times more malate in leaves, and accumulated more of the accompanying cation than seedlings treated with NaNO3. Within seedlns of each treatment, changes in nitrate reductase activity and malate accumulation were parallel in leaves and in roots. Despite the great difference in malate accumulation, leaves of the KNO3-treated seedlgs had only slightly greater levels of phosphoenolpyruvate carboxylase than leaves of NaNO3-treated seedlings. NADP-malic enzyme levels increased only slightiy in leaves and roots of both KNO3-and NaNO3-treated seedlns. The effects of K+ and Na+ on all of these parameters can best be explained by their effects on nitrate translocation, which in turn affects the other parameters. In a separate experiment, we confirmed that phospboenolpyruvate carboxylase activity increased about 2-fold during 36 hours of KNO3 treatment, and increased only slightly in the KCI control.(2), in which K+ is an integral part of a NO3--malate shuttle between roots and shoots.Jackson and Coleman (10) first showed the presence of PEP carboxylase in roots, and proposed the PEP carboxylase-malic dehydrogenase pathway for malate accumulation in roots. This pathway, together with malic enzyme for decarboxylation of malate, have been proposed as a mechanism for pH regulation during nitrate assimilation (18, 21), but the hypothesis has not been explicitly tested. We report here the effects of NO3 and its salts on changes in activity of carboxylating and decarboxylating enzymes.Dijkshoorn et al. (6) have shown that internal HCO3, from the decarboxylation of organic acids, was exchanged for external N03 . Also, Ben-Zioni et al. (2) have shown that tobacco roots can secrete more H"CO3-into the medium when N03 is supplied than when Cl-is supplied. The source of H14CO3 was most likely malate, previously synthesized from 14C02 supplied to the leaves.These data also implied an exchange of HCO3 for external NO3.Since there is no a priori reason why this exchange should depend on the presence of K+, we predicted that activity of the reputed decarboxylase, NADP malic enzyme (5), should not be affected by the cation accompanying N03 in the medium. This prediction was fulfilled by experiment.Both the effects of N03-on cation uptake (3, 11) and the effects of different cations on N03-uptake have been studied (4, 15). In some experiments N03 uptake from KNO3 and NaNO3 were nearly the same (16 (Plant Physiol. 56: S-227, 1975 MATERIALS AND METHODSSeeds of wheat (Triticum vulgare L. cv. Arthur) were cultured according to the methods of Blevins et al. (3). The seeds were soaked for 24 hr in continuously aerated deionized ...

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“…Nitrate delivery via the xylem to the shoot is depressed (17), and N03 reduction in the leaves declines (12,17). Although phloem transport of assimilated N to N sinks is eventually reduced (4, 25), it is probable that phloem transport is sufficiently resistant to water stress to permit appreciable salvage of both N and carbon from wilted leaves that are dying as a consequence of desiccation (3,6,25).…”

Section: Introductionmentioning

confidence: 99%

Proline Accumulation in Water-stressed Barley Leaves in Relation to Translocation and the Nitrogen Budget

Tully¹,

Hanson²,

Nelsen³

1979

Plant Physiol.

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Mobilization of N from leaves of barley (Hordeum vulgare L.) during water stress, and the role of proline as a mobilized species, were examined in plants at the three-leaf stage. The plants responded to water stress by withdrawing about 25% of the total reduced N from the leaf blades via phloem translocation. Most of this N loss was during the first 2 days while translocation of 'C-photosynthate out of the stressed blade still remained active. Free proline accumulation in the blade was initially slow, and became more rapid during the 2nd day of stress. Although a major free amino acid, proline accounted for only about 5% of the total N (soluble + insoluble) retained in severely stressed blades. When the translocation pathway in water-stressed leaves was interrupted just below the blade by a heat girdle, a cold jacket, or by blade excision, N loss from the blade was prevented and proline began to accumulate rapidly on 1st day of stress. Little free proline accumulated in the blades until after the ability to translocate was lost. Proline was, however, probably not a major species of N translocated during stress, because proline N accumulation in heatgirdled stressed leaves was five times slower than the rate of total N export from intact blades.The onset of water deficit alters the over-all N budget of crops through effects on both N transport and N assimilation. Nitrate delivery via the xylem to the shoot is depressed (17), and N03 reduction in the leaves declines (12,17). Although phloem transport of assimilated N to N sinks is eventually reduced (4, 25), it is probable that phloem transport is sufficiently resistant to water stress to permit appreciable salvage of both N and carbon from wilted leaves that are dying as a consequence of desiccation (3,6,25).Within the leaves of many plants subjected to moderate or severe water stress, one striking change in N metabolism is the accumulation of free proline as a result of net de novo synthesis from glutamic acid (e.g. 1, 2). It has been proposed that this accumulation is a metabolic adaptation which confers survival value, perhaps acting as a (phloem-mobile) reserve of N accessible for use upon stress relief (e.g. 1,18,21). This possibility cannot be evaluated without knowing: (a) how much N is exported from stressed leaves to other parts of the plant; and (b) whether proline accumulation and export are significant terms in the total N budget of a leaf during stress. Much of the published work on proline accumulation during water stress has been with detached leaves, which clearly cannot export N. Proline accumulation has also been investigated in intact plants. In Plants were grown in Perlite in plastic pots (7 x 12 cm) for 17 to 19 days after sowing (to the three-leaf stage) in a growth chamber under a regime of 16-h days, day/night temperature 22/ 16 C, day/night RH 70/85%, total irradiance 3.8 mw cm-2 (80%o from fluorescent lamps, 20o from incandescent lamps), and were watered on alternate days with half-strength Hoagland solution.Prior to the exper...

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Nitrate Reductase Activity in Maize (Zea mays L.) Leaves

Cited by 143 publications

References 16 publications

Modification of Leaf Apoplastic pH in Relation to Stomatal Sensitivity to Root-Sourced Abscisic Acid Signals

Modification of Leaf Apoplastic pH in Relation to Stomatal Sensitivity to Root-Sourced Abscisic Acid Signals

Role of Potassium and Malate in Nitrate Uptake and Translocation by Wheat Seedlings

Proline Accumulation in Water-stressed Barley Leaves in Relation to Translocation and the Nitrogen Budget

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