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1.
Nitrogen form has been shown to affect Zn uptake, translocation and storage in the Zn-hyperaccumulating plant Noccaea caerulescens but the biochemical processes are not fully understood. Organic acids and amino acids have been implicated in Zn transport and storage. This study aimed to examine the effect of N form on concentrations of organic acids and amino acids and how these metabolites correlated with Zn hyperaccumulation. Plants were grown in nutrient solution with NO3−, NH4NO3 or NH4+, supplied with 50 or 300 μM Zn, and buffered at either pH 4.5 or 6.5. The metabolomic profile was determined by gas chromatography mass spectroscopy. The concentration of Zn in shoots, xylem and roots was greatest for the NO3−, pH 6.5 and 300 μM Zn treatments. For all N forms, the lower growth-medium pH raised xylem sap pH but had no influence on Zn concentration or exudation rate of the xylem sap. Nitrate enhanced organic acid production while NH4+ increased amino acid production. Organic acids in the xylem were more responsive to changes in growth-medium pH than N form, and did not correlate with Zn concentration in shoots, roots or xylem. Serine might be directly involved in Zn hyperaccumulation. Phosphoric acid was associated with reduced Zn accumulation in the shoots. Malic acid was not detected in the shoots but responded to cation uptake more than to Zn specifically in the roots. Citric acid responded to cation uptake more than to Zn specifically in the shoots but did not correlate with Zn concentration in the roots or the xylem sap, or any other cations in the roots. In conclusion, organic acids in N. caerulescens are not specifically involved in Zn hyperaccumulation but are involved in regulating pH in the xylem and cation–anion balance in plants. 相似文献
2.
The effect of ectomycorrhizal association of Pinus pinaster with Hebeloma cylindrosporum was investigated in relation to the nitrogen source supplied as mineral (NH4+ or NO3?) or organic N (L ‐glutamate) and at 5 mol m?3. Plants were grown for 14 and 16 weeks with mineral and organic N, respectively, and samples were collected during the last 6 weeks of culture. Total fungal biomass was estimated using glucosamine amount and its viability was assessed using the glucosamine to ergosterol ratio. Non‐mycorrhizal plants grew better with NH4+ than with NO3? and grew very slowly when supplied with L ‐glutamate. The presence of the fungus decreased the growth of the host plant with mineral N whereas it increased it with L ‐glutamate. Whatever the N source, most of the living fungal biomass was associated with the roots, whereas the main part of the total biomass was assayed outside the root. The form of mineral N did not significantly affect N accumulation rates over the 42 d in control plants. In mycorrhizal plants grown on either N source, the fungal tissues developing outside of the root were always the main N sink. The ectomycorrhizal association did not change 15NH4+ uptake rate by roots, suggesting that the growth decrease of the host‐plant was related to the carbon cost for fungal growth and N assimilation rather than to a direct effect on NH4+ acquisition. In contrast, in NO3?‐grown plants, in addition to draining carbon for NO3? reduction the fungus competed with the root for NO3? uptake. With NH4+ or NO3? feeding, although mycorrhizal association improved N accumulation in shoots, we concluded that it was unlikely that the fungus had supplied the plant with N. In L ‐glutamate‐grown plants, the presence of the fungus increased the proportion of glutamine in the xylem sap and improved both N nutrition and the growth rate of the host plant. 相似文献
3.
Abstract Tomato plants (Lycopersicon esculentum Mill. cv. San Marzano), grown in dilute nutrient solutions containing (in meq ˙ 1-1) 0.5 NaNO3, 0.5 NH4NO3 or 0.25 (NH4)2 SO4 as the nitrogen source, were detopped for collection of xylem sap and measurement of trans-root electrical potentials. The plant parts and the xylem exudate were subsequently analysed for mineral content. The commonly observed effects of NH4+ were noted, including reduction of calcium concentration in the xylem sap, and of calcium content in stems and leaves, compared with NO3-fed plants. This effect was attributed principally to the less negative trans-root electrical potential measured in NH4+-fed plants, and the resultant reduction of inward driving force on passively moving divalent cations. 相似文献
4.
The Influence of Nitrate and Ammonium Nutrition on the Growth of Wheat (Triticum aestivum) and Maize (Zea mays) Plants 总被引:3,自引:0,他引:3
The effects of NO-3 and NH+4 nutrition on hydroponically grownwheat (Triticum aestivum L.) and maize (Zea mays L.) were assessedfrom measurements of growth, gas exchange and xylem sap nitrogencontents. Biomass accumulation and shoot moisture contents ofwheat and maize were lower with NH+4 than with NO-3 nutrition.The shoot:root ratios of wheat plants were increased with NH+4compared to NO-3 nutrition, while those of maize were unaffectedby the nitrogen source. Differences between NO-3 and NH+4-fedplant biomasses were apparent soon after introduction of thenitrogen into the root medium of both wheat and maize, and thesedifferences were compounded during growth. Photosynthetic rates of 4 mM N-fed wheat were unaffected bythe form of nitrogen supplied whereas those of 12 mM NH+4-fedwheat plants were reduced to 85% of those 12 mM NO-3-fed wheatplants. In maize supplied with 4 and 12 mM NH+4 the photosyntheticrates were 87 and 82% respectively of those of NO-3-fed plants.Reduced photosynthetic rates of NH+4 compared to NO-3-fed wheatand maize plants may thus partially explain reduced biomassaccumulation in plants supplied with NH+4 compared to NO-3 nutrition.Differences in the partitioning of biomass between the shootsand roots of NO-3-and NH+4-fed plants may also, however, arisefrom xylem translocation of carbon from the root to the shootin the form of amino compounds. The organic nitrogen contentof xylem sap was found to be considerably higher in NH+4- thanin NO-3-fed plants. This may result in depletion of root carbohydrateresources through translocation of amino compounds to the shootin NH+4-fed wheat plants. The concentration of carbon associatedwith organic nitrogen in the xylem sap of maize was considerablyhigher than that in wheat. This may indicate that the shootand root components of maize share a common carbon pool andthus differences induced by different forms of inorganic nitrogenare manifested as altered overall growth rather than changesin the shoot:root ratios.Copyright 1993, 1999 Academic Press Triticum aestivum, wheat, Zea mays, maize, nitrogen, growth, photosynthesis, amino acids, xylem 相似文献
5.
The results of the experiments discussed here present changes in the chemical composition of xylem sap of tomato seedlings cultivated in hydroponics on media containing 5 mmol HCO3
– and an N-source given as NO3
–, NH4
+ or these two forms in different proportions. The occurrence of free NH4
+ in the xylem sap of NH4
+-seedlings and in NO3
–-seedlings indicates that the process of N-assimilation was not only confined to roots. The application of HCO3
– to the medium effected a decrease in the concentration of NH4
+ in the xylem sap of NH4
+-seedlings, having no effect on changes in the concentration of NO3
– or NH4
+ in NO3
–-seedlings. Malate, citrate, fumarate, and succinate were identified in the xylem sap. The concentration of carboxylates in NO3
–-seedlings exceeded by about 50% that recorded in NH4
+-seedlings. The highest concentration of malate constituting from 80% to 93.5% of this fraction, was determined in this group of compounds. The enrichment of the medium with HCO3
– ions induced an increase in the content of carboxylates, chiefly of malate. In these experimental conditions an increase in the malate concentration in the xylem sap of NO3
– and NH4
+-seedlings reached relative values of 100% and 36%, respectively. The total concentration of amides and amino acids was about 2.6 times higher in the xylem sap of NH4
+-seedlings than in NO3
–-seedlings. Amide glutamine was the main component of this fraction in xylem sap and its total concentration was about 3.3 times higher in NH4
+-seedlings than that determined in NO3
–-seedlings. Glutamine, glutamate, aspargine, and aspartate constituted from 69% to 77% of this fraction. The concentration of the remaining amino acids varied from 0.6% to 7%. The enrichment of the medium with HCO3
– ions also effected an increase in the concentration of amides and amino acids in the xylem sap by about 17% and 56% in the case of NO3
– and NH4
+-seedlings, respectively, in comparison with the respective controls (without HCO3
–).
Abbreviations: DAG – days after germination; DIC – dissolved inorganic carbon; GOGAT – glutamine:2-oxoglutarate aminotransferase; GS – glutamine synthetase; PAR – photosynthetically active radiation; PEPc – phosphoenolpyruvate carboxylase 相似文献
6.
Changes in the xylem exudate composition of poplar Populus tremula x P. alba)-dependent on the nitrogen 总被引:1,自引:0,他引:1
The capacity of poplar (P. tremula x P.
alba, clone INRA 717 1/B4) to respond to changes in the nutrient
supply with modifications in the xylem exudate collected after decapitation
was investigated with special respect to N-compounds. The composition
(inorganic ions and amino-N) was analysed with respect to (a) the time
after decapitation at different times of day, (b) a change in the nitrogen
concentration from NO-3 to N-free medium, a change
in the nitrogen source from NO-3 to
NH+4, (d) an increase in NO-3
supply from 1 mM to 8 mM, and (e) the withdrawal of
K+ supply. (a) The ion concentration in the xylem
exudate was not affected up to 15 min after decapitation of the plants.
Later a continuous increase in the concentration was observed. This
increase was large if decapitation was performed in the middle of the light
period and small at night-time. In both types of experiments (b,c) the
NO-3 concentration dropped immediately after the
transfer, indicating the close connection between
NO-3 uptake and xylem loading. (b) After transfer to
N-free medium poplar did not balance the charge in the xylem by increasing
the concentration of other inorganic anions or decreased xylem loading of
cations within 3 d of treatment. The N-status of the xylem exudate was
reduced within 15 min. After transfer of the
NO-3-grown plants to NH+4, as
the sole N-source, the charge compensation in the xylem exudate was
maintained by reducing the loading of cations, and 3 d later by an enhanced
xylem loading of mainly SO24-. The N-status in the
xylem exudate was maintained by an immediate increase in glutamine
concentration (2-fold in 15 min). (d) Increasing the
NO-3 supply to 8 mM had no effect on the ionic
composition or the N-status of the xylem exudate. (e) The withdrawal of
K+ from the medium for 11 d resulted in a limitation
of the S- and N-supply of the plant, causing a decrease in the N-status of
the xylem sap. The data are discussed with respect to charge compensation
after changes in the nutrient supply and to the maintenance of the nitrogen
status in the xylem sap. 相似文献
7.
In order to investigate the effects of homogeneous and localized supply of different nitrogen forms (nitrate, NO3 ? vs ammonium, NH4 +) on the growth of tomato seedlings, root morphology and six cytokinin (CTK) fractions in xylem sap were analyzed. Whole roots were supplied with different ratios of NO3 ? to NH4 + (100:0, as 100-0NA; 75:25, as 75-25NA; 50:50, as 50-50NA) under homogeneous supply. In split-root experiments, three treatments were compared: a sole NO3 ? supply (N|N), a spatially separated supply of NO3 ? and NH4 + (N|A), and a spatially separated supply of NO3 ? and a mixture of NO3 ? and NH4 + nutrition at a ratio of 75:25 (N|AN). All concentrations of total N were set at 5 mM. The results showed that (1) homogeneous 75% NO3 ? plus 25% NH4 + supply to the whole root zone led to maximum shoot and root dry matter (DM), root surface area (RS) and root volume (RV). The spatially separated supply of NO3 ? and NH4 + (N|A) resulted in a contrasting effect on root morphology: in comparison to N|N, root DM in the NO3 ?-containing pot was increased by 50% whereas it was depressed by 50% in the NH4 +-containing pot. The 75% NO3 ? plus 25% NH4 + supply in the split-root experiment led to no significant effects either on shoot DM and root DM, or on RS and RV when compared to N|N. (2) The presence of NH4 + in the external medium led to a significantly reduced total xylem-CTK concentration, and a close negative correlation was found between xylem NH4 + and total CTK concentration irrespective of culture mode. A relatively high level of zeatin riboside (ZR) was maintained both in 75-25NA and N|A treatments. It was concluded that, in addition to the percentage of NH4 + to NO3 ? in the nutrient solution, whether NH4 + was supplied to the whole root system or to only part of the root system was also an important factor affecting plant growth. The fact that the 75-25NA and N|A treatments resulted in optimal growth of tomato seedlings might be attributed to the higher ZR concentration in xylem. 相似文献
8.
B. J. Atwell 《Plant and Soil》1992,139(2):247-251
Two cultivars of Lupinus angustifolius L. were grown in a glasshouse in solutions containing NO3
-, NH4
+ or NH4NO3 with a total nitrogen concentration of 2.8 M m-3 in each treatment. One cultivar chosen (75A-258) was relatively tolerant to alkaline soils whereas the other (Yandee) was intolerant to alkalinity. Controlled experiments were used to assess the impact of cationic vs. anionic forms of nitrogen on the relative performance of these cultivars. Relative growth rates (dry weight basis) were not significantly different between the two cultivars when grown in the presence of NO3
-, NH4
+ or NH4NO3. However, when NO3
- was supplied, there was a modest decline in relative growth rates in both cultivars over time. When plants grown on the three sources of nitrogen for 9 days were subsequently supplied with 15NH4NO3 or NH4
15NO3 for 30 h, NH4
+ uptake was generally twice as fast as NO3
- uptake, even for plants grown in the presence of NO3
-. Low rates of NO3
- uptake accounted for the decrease in growth rates over time when plants were grown in the presence of NO3
-. It is concluded that the more rapid growth of 75A-258 than Yandee in alkaline conditions was not due to preferential uptake of NH4
+ and acidification of the external medium. In support of this view, acidification of the root medium was not significantly different between cultivars when NH4
+ was the sole nitrogen source. 相似文献
9.
M. ASHRAF 《The Annals of applied biology》1999,135(2):509-513
The effects of the ammonium (NH4+) and nitrate (NO3-) forms of nitrogen and NaCl on the growth, water relations and photosynthesis performance of sunflower (Helianthus annuus L.) were examined under glasshouse conditions. Eight-day-old plants of cv. Hisun 33 were subjected for 21 days to Hoagland's nutrient solution containing 8 mol m-3N as NH4+or NO3-, and salinised with 0, 60, or 120 mol m-3NaCl. Fresh weights of shoots and roots, and leaf area of NO3-supplied non-salinised plants were significantly greater than those of NH4+-supplied non-salinised plants. But addition of NaCl to the rooting medium of these plants had more inhibitory effect on the growth of NO3--supplied plants than on NH4+-supplied plants. Both leaf water and osmotic potentials of plants grown with NH4+were lower than those of plants given NO3-under both non-saline and saline conditions. Chlorophylls a and b concentrations were higher in plants grown with NH4+than N03--supplied plants at the lower two levels of salinisation. The rate of photosynthesis in plants was considerably higher in non-salinised plants grown with NO3-than with NH4+, but with increase in salinisation the photosynthesis rate decreased in NO3--supplied plants, but not in those given NH4+. The rate of transpiration was increased significantly by salinisation in NO3--supplied plants, but not consistently so in NH4+-supplied plants. The stomatal conductances were much higher in plants given NO3-than with NH4+when grown under non-saline conditions, but not when salinised. As a consequence, water-use efficiency in NO3--supplied control plants was better than in NH4+-supplied under non-saline conditions, but worse under saline conditions. The different forms of nitrogen and the addition of NaCl to the growing medium did not affect the relative intercellular concentrations of CO2 (Ci/Ca). Overall, the NH4+form of nitrogen inhibited the growth of sunflowers under non-saline conditions, but NO3-and NaCl interacted to inhibit growth more than did NH4+under saline conditions. 相似文献
10.
Growth, chemical composition, and nitrate reductase activity (NRA) of hydroponically cultured Rumex crispus, R. palustris, R. acetosa, and R. maritimus were studied in relation to form (NH4
+, NO3
-, or both) and level of N supply (4 mM N, and zero-N following a period of 4mM N). A distinct preference for either NH4
+ or NO3
- could not be established. All species were characterized by a very efficient uptake and utilization of N, irrespective of
N source, as evident from high concentrations of organic N in the tissues and concurrent excessive accumulations of free NO3
- and free NH4
+. Especially the accumulation of free NH4
+ was unusually large.
Generally, relative growth rate (RGR) was highest with a combination of NH4
+ and NO3
-. Compared to mixed N supply, RGR of NO3
-- and NH4
+-grown plants declined on average 3% and 9%, respectively. Lowest RGR with NH4
+ supply probably resulted from direct or indirect toxicity effects associated with high NH4
+ and/or low Ca2+ contents of tissues. NRA in NO3
- and NH4NO3 plants was very similar with maxima in the leaves of ca 40 μmol NO2
- g-1 DW h-1. ‘Basal’ NRA levels in shoot tissues of NH4
+ plants appeared relatively high with maxima in the leaves of ca 20 μmol NO2
- g-1 DW h-1. Carboxylate to organic N ratios, (C-A)/Norg, on a whole plant basis varied from 0.2 in NH4
+ plants to 0.9 in NO3
- plants.
After withdrawal of N, all accumulated NO3
- and NH4
+ was assimilated into organic N and the organic N redistributed on a large scale. NRA rapidly declined to similar low levels,
irrespective of previous N source. Shoot/root ratios of -N plants were 50–80% lower than those from +N plants. In comparison
with +N, RGR of -N plants did not decline to a large extent, decreasing by only 15% in -NH4
+ plants due to very high initial organic-N contents. N-deprived plants all exhibited an excess cation over anion uptake (net
proton efflux), and whole-plant (C-A)/Norg ratios increased to values around unity.
Possible difficulties in interpreting the (C-A)/Norg ratio and NRA of plants in their natural habitats are briefly discussed. 相似文献
11.
Interaction between atmospheric and pedospheric nitrogen nutrition in spruce (Picea abies L. Karst) seedlings 总被引:4,自引:2,他引:4
The effect of NO2 fumigation on root N uptake and metabolism was investigated in 3-month-old spruce (Picea abics L. Karst) seedlings. In a first experiment, the contribution of NO2 to the plant N budget was measured during a 48 h fumigation with 100mm3m?3 NO2. Plants were pre-treated with various nutrient solutions containing NO2 and NH4+, NO3? only or no nitrogen source for 1 week prior to the beginning of fumigation. Absence of NH4+ in the solution for 6d led to an increased capacity for NO3? uptake, whereas the absence of both ions caused a decrease in the plant N concentration, with no change in NO3? uptake. In fumigated plants, NO2 uptake accounted for 20–40% of NO3? uptake. Root NO3? uptake in plants supplied with NH4+plus NO3? solutions was decreased by NO2 fumigation, whereas it was not significantly altered in the other treatments. In a second experiment, spruce seedlings were grown on a solution containing both NO2 and NH4+ and were fumigated or not with 100mm3m?3 NO2 for 7 weeks. Fumigated plants accumulated less dry matter, especially in the roots. Fluxes of the two N species were estimated from their accumulations in shoots and roots, xylem exudate analysis and 15N labelling. Root NH4+ uptake was approximately three times higher than NO3? uptake. Nitrogen dioxide uptake represented 10–15% of the total N budget of the plants. In control plants, N assimilation occurred mainly in the roots and organic nitrogen was the main form of N transported to the shoot. Phloem transport of organic nitrogen accounted for 17% of its xylem transport. In fumigated plants, neither NO3? nor NH4+ accumulated in the shoot, showing that all the absorbed NO2 was assimilated. Root NO3? reduction was reduced whereas organic nitrogen transport in the phloem increased by a factor of 3 in NO2-fimugated as compared with control plants. The significance of the results for the regulation of whole-plant N utilization is discussed. 相似文献
12.
Although NH4
+ has generally been accepted as the preferred N source for fertilising rice, some workers have concluded tha NO3
- is as effective as NH4
+. The present glasshouse study exmined the relative uptake of NH4
+ and NO3
- from solution and cultures containing 5–120 mg N/L supplied as NH4NO3 by a hybrid rice (India) and a conventional rice cultivar (Japonica). At all levels of N supply, the hybrid rice had higher leaf area and higher rates of uptake of total N than the conventional cultivar. Net photosynthesis rates were similar for both cultivars at the highest rates of N supply, but were lower at 5–40 mg N/L for the hybrid cultivar than for the conventional cultivar. At all levels of N supply, the conventional rice cultivar absorbed more NH4
+ than NO3
-. In contrast, the hybrid rice absorbed more NH4
+ than NO3
- at the low levels of N supply (5–40 mg N/L), but more NO3
- than NH4
+ at the high levels of at 80 and 120 mg N/L. It is concluded that the uptake of N by rice is under genetic control and also dependent on levels of N supply. Thus the appropriate form of N fertiliser for rice may depend on cultivar and rates of N supply. 相似文献
13.
Rafael de Souza Miranda Juan Carlos Alvarez-Pizarro Celso Marinones Silva Araújo José Tarquinio Prisco Enéas Gomes-Filho 《Acta Physiologiae Plantarum》2013,35(3):841-852
This work aimed to study the regulation of K+/Na+ homeostasis and the physiological responses of salt-treated sorghum plants [Sorghum bicolor (L.) Moench] grown with different inorganic nitrogen (N) sources. Four days after sowing (DAS), the plants were transferred to complete nutrient solutions containing 0.75 mM K+ and 5 mM N, supplied as either NO3 ? or NH4 +. Twelve DAS, the plants were subjected to salt stress with 75 mM NaCl, which was applied in two doses of 37.5 mM. The plants were harvested on the third and seventh days after the exposure to NaCl. Under the salt stress conditions, the reduction of K+ concentrations in the shoot and roots was higher in the culture with NO3 ? than with NH4 +. However, the more conspicuous effect of N was on the Na+ accumulation, which was severely limited in the presence of NH4 +. This ionic regulation had a positive influence on the K+/Na+ ratio and the selective absorption and transport of K+ in the plants grown with NH4 +. Under control and salt stress conditions, higher accumulation of free amino acids and soluble proteins was promoted in NH4 + grown roots than NO3 ? grown roots at both harvesting time, whereas higher accumulation of soluble sugars was observed only at 7 days of salt stress exposure. Unlike the NH4 + grown plants, the gas exchanges of the NO3 ? grown plants were reduced after 7 days of salt stress. These results suggest that external NH4 + may limit Na+ accumulation in sorghum, which could contribute to improving its physiological and metabolic responses to salt stress. 相似文献
14.
Our previous work indicated that salinity caused a shift in the predominant site of nitrate reduction and assimilation from the shoot to the root in tomato plants. In the present work we tested whether an enhanced supply of dissolved inorganic carbon (DIC, CO2+ HCO3) to the root solution could increase anaplerotic provision of carbon compounds for the increased nitrogen assimilation in the root of salinity-stressed Lycopersicon esculentum (L.) Mill. cv. F144. The seedlings were grown in hydroponic culture with 0 or 100mM NaCl and aeration of the root solution with either ambient or CO2-enriched air (5000 μmol mol?1). The salinity-treated plants accumulated more dry weight and higher total N when the roots were supplied with CO2-enriched aeration than when aerated with ambient air. Plants grown with salinity and enriched DIC also had higher rates of NO?3 uptake and translocated more NO?3 and reduced N in the xylem sap than did equivalent plants grown with ambient DIC. Incorporation of DIC was measured by supplying a 1 -h pulse of H14CO?3 to the roots followed by extraction with 80% ethanol. Enriched DIC increased root incorporation of DIC 10-fold in both salinized and non-salinized plants. In salinity-stressed plants, the products of dissolved inorganic 14C were preferentially diverted into amino acid synthesis to a greater extent than in non-salinized plants in which label was accumulated in organic acids. It was concluded that enriched DIC can increase the supply of N and anaplerotic carbon for amino acid synthesis in roots of salinized plants. Thus enriched DIC could relieve the limitation of carbon supply for ammonium assimilation and thus ameliorate the influence of salinity on NO?3 uptake and assimilation as well as on plant growth. 相似文献
15.
《Journal of Plant Interactions》2013,8(1):514-520
A pot experiment was conducted to investigate the organic phosphorus (P) (phytate) utilization of Zea mays L. with different nitrogen (N) forms (NH4+ and NO3?) when both arbuscular mycorrhizal (AM) fungus (Funelliformis mosseae) and phosphate-solubilizing bacterium (PSB, Pseudomonas alcaligenes) are present. The soil was supplied with either KNO3 or (NH4)2SO4 (200 mg kg?1 N) with or without phytin (75 mg P kg?1). Results showed that the application of NH4+ to the soil in a plant–AM fungus–PSB system decreased rhizosphere pH and increased phosphatase activity. It also enhanced the mineralization rate of phytin, which resulted in the release of more inorganic P. The application of NO3? promoted mycorrhizal colonization and hyphal length density in the soil. The inorganic P in the hyphosphere decreased, but more P was transferred to the plant through the mycorrhizal hyphae. Hence, in addition, the application of the two different N forms did not significantly alter the content of plant P. The plant supplied with different N fertilizers acquired P through different mechanisms associated with other microbes. NH4+ application promoted phytin mineralization by decreasing soil pH, whereas NO3? application increased inorganic P uptake by strengthening the mycorrhizal pathway. 相似文献
16.
Assimilation and Transport of Nitrogen in Nonnodulated (NO(3)-grown) Lupinus albus L 总被引:7,自引:7,他引:0
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The response of nonnodulated white lupin (Lupinus albus L. cv. Ultra) plants to a range of NO3 levels in the rooting medium was studied by in vitro assays of extracts of plant parts for NO3 reductase (EC 1.6.6.1) activity, measurements of NO3-N in plant organs, and solute analyses of root bleeding (xylem) sap and phloem sap from stems and petioles. Plants were grown for 65 days with 5 millimolar NO3 followed by 10 days with 1, 5, 15, or 30 millimolar NO3. NO3 reductase was substrate-induced in all tissues. Roots contained 76, 68, 62 and 31% of the total NO3 reductase activity of plants fed with 1, 5, 15, and 30 millimolar NO3, respectively. Stem, petioles, and leaflets contained virtually all of the NO3 reductase activity of a shoot, the activity in extracts of fruits amounting to less than 0.3% of the total enzyme recovered from the plant. Xylem sap from NO3-grown nonnodulated plants contained the same organic solutes as from nodulated plants grown in the absence of combined N. Asparagine accounted for 50 to 70% and glutamine 10 to 20% of the xylem-borne N. The level of NO3 in xylem sap amounted to 4, 13, 12, and 17% of the total xylem N at 1, 5, 15, and 30 millimolar NO3, respectively. Xylem to phloem transfer of N appeared to be quantitatively important in supplying fruits and vegetative apices with reduced N, especially at low levels of applied NO3. NO3 failed to transfer in any quantity from xylem to phloem, representing less than 0.3% of the phloem-borne N at all levels of applied NO3. Shoot organs were ineffective in storing NO3. Even when NO3 was supplied in great excess (30 millimolar level) it accounted for only 8% of the total N of stem and petioles, and only 2 and 1% of the N of leaflets and fruits, respectively. 相似文献
17.
The impact of photoperiod on the rate and magnitude of N remobilization relative to uptake of inorganic N during the recovery of shoot growth after a severe defoliation was compared over 18 days in two temperate grass species, timothy (Phleum pratense L. cv. Bodin) and meadow fescue (Festuca pratensis Huds. cv. Salten). Plants were grown in flowing solution culture with N supplied as 20 mM NH4NO3 and pre-treated by extending the 11 h photosynthetically significant light period either by 1 h (short-day or SD plants) or 7 h (long-day or LD plants) of very low light intensity, during the 10 days prior to defoliation. Following a single severe defoliation, 15N-labelled NH4+ or NH4++ NO3? was supplied over a 20-day recovery period under the same SD and LD conditions. Changes in the relative contributions of remobilized N and newly acquired mineral N to shoot regrowth were assessed by sequential harvests. Both absolute and relative rates of N remobilization from root and stubble fractions were higher in LD than SD plants of both species, with the enhancement more acute but of shorter duration in timothy than fescue. Remobilized N was the predominant source of N for shoot regrowth in all treatments between days 0 and 8 after cutting; on average more so for fescue than timothy, because the presence of NO3? reduced the proportional contribution of remobilized N to the regrowth of timothy but not of fescue. Net uptake of mineral N began to recover between days 4 and 6 after cutting, with NO3? uptake restarting 1 or 2 days earlier than NH4+ uptake, even when NH4+ was the only form of N supply. LD timothy plants supplied solely with NH4+ were slowest to resume uptake of mineral N. Supplying NO3? in addition to NH4+ after defoliation promoted shoot regrowth rate but not remobilization of N. Rates of regrowth (shoot dry weight production per plant) were not correlated with rates of N remobilization from stubble either over the short-term (days 0–8) or longer term (days 0–18), interpreted as evidence against a causal dependence of regrowth rate on N remobilization under these conditions. The results are discussed in relation to hypotheses for source/sink-driven rates of N remobilization and their interactions with mineral N uptake following defoliation. 相似文献
18.
Ionic Balance of Root-Shoot Nitrate Transfer in Dwarf Bean 总被引:1,自引:0,他引:1
The Dijkshoorn-Ben Zioni model about potassium recycling in higher plants proposes a stoichiometric coupling between the upward transport of nitrate and potassium, and therefore a 1:1 ratio of these ions in the xylem sap. Phaseolus vulgaris grown in media with different NO3: K+ ratios, however, only rarely showed equimolar concentrations of the two ions in the bleeding sap. Ratios between 0.2 and 11 were observed and the ratios between concentrations of the ions in the exudate and in the external solution were positively correlated. An analysis of the major inorganic constituents of the exudate revealed an ionic balance that requires negligible amounts of charges from organic molecules. 相似文献
19.
Nitrogen Nutrition and Xylem Transport of Nitrogen in Ureide-producing Grain Legumes 总被引:18,自引:16,他引:2
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Xylem sap composition was examined in nodulated and nonnodulated cowpea (Vigna unguiculata [L.] Walp.) plants receiving a range of levels of NO3 and in eight other ureide-forming legumes utilizing NO3 or N2 as sole source of nitrogen. A 15N dilution technique determined the proportions of plant nitrogen derived from N2 in the nodulated cowpeas fed NO3. Xylem sap composition of NO3-fed, nodulated cowpea varied predictably with the relative extents to which N2 and NO3 were being utilized. The ratios of asparagine to glutamine (N/N) and of NO3 to ureide (N/N) in xylem sap increased with increasing dependence on NO3 whereas per cent of xylem nitrogen as ureide and the ratio of ureide plus glutamine to asparagine plus NO3 (N/N) in xylem sap increased with increasing dependence on N2 fixation. The amounts of NO3 and ureides stored in leaflets, stems plus petioles, and roots of cowpea varied in a complex manner with level of NO3 and the presence or absence of N2 fixation. All species showed higher proportions of organic nitrogen as ureide and several-fold lower ratios of asparagine to glutamine in their xylem sap when relying on N2 than when utilizing NO3. In nodulated (minus nitrate) cowpea and mung bean (Vigna radiata [L.] Wilczek) the percentage of xylem nitrogen as ureide remained constant during growth but the ratio of asparagine to glutamine varied considerably. The biochemical significance of the above differences in xylem sap composition was discussed. 相似文献
20.
Absorption of nitrate and ammonium ions by Lolium perenne from flowing solution cultures at low root temperatures 总被引:3,自引:1,他引:2
Lolium perenne L. cv. 23 (perennial ryegrass) plants were grown in flowing solution culture and acclimatized over 49 d to low root temperature (5°C) prior to treatment at root temperatures of 3, 5, 7 and 9°C for 41 d with common air temperature of 20/15°C day/night and solution pH 5·0. The effects of root temperature on growth, uptake and assimilation of N were compared with N supplied as either NH4 or NO3 at 10 mmol m?3. At any given temperature, the relative growth rate (RGR) of roots exceeded that of shoots, thus the root fraction (Rf) increased with time. These effects were found in plants grown with the two N sources. Plants grown at 3 and 5°C had very high dry matter contents as reflected by the fresh weight: freeze-dried weight ratio. This ratio increased sharply, especially in roots at 7 and 9°C. Expressed on a fresh weight basis, there was no major effect of root temperature on the [N] of plants receiving NHJ but at any given temperature, the [N] in plants grown with NHJ was significantly greater than in those grown with NO3. The specific absorption rate (SAR) of NH+4 was greater at all temperatures than SAR-NO3. In plants grown with NH+, 3–5% of the total N was recovered as NH+4, whereas in those grown with NO?3 the unassimilated NO?3 rose sharply between 7 and 9°C to become 14 and 28% of the total N in shoots and roots, respectively. The greater assimilation of NH+4 lead to concentrations of insoluble reduced N (= protein) which were 125 and 20% greater, in roots and shoots, respectively, than in NO?3-grown plants. Plants grown with NH+4 had very much greater glutamine and asparagine concentrations in both roots and shoots, although other amino acids were more similar in Concentration to those in NO?3 grown plants. It is concluded that slow growth at low root temperature is not caused by restriction of the absorption or assimilation of either NH+4 or NO?3. The additional residual N (protein) in NH+4 grown plants may serve as a labile store of N which could support growth when external N supply becomes deficient. 相似文献