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1.
Ann Oaks Ineke Stulen Karen Jones Michael J. Winspear Santosh Misra Ingrid L. Boesel 《Planta》1980,147(5):477-484
The intracellular distribution of enzymes involved in the Crassulacean acid metabolism (CAM) has been studied in Bryophyllum calycinum Salisb. and Crassula lycopodioides Lam. After separation of cell organelles by isopycnic centrifugation, enzymes of the Crassulacean acid metabolism were found in the following cell fractions: Phosphoenolpyruvate carboxylase in the chloroplasts; NAD-dependent malate dehydrogenase in the mitochondria and in the supernatant; NADP-dependent malate dehydrogenase and phosphoenolpyruvate carboxykinase in the chloroplasts; NADP-dependent malic enzyme in the supernatant and to a minor extent in the chloroplasts; NAD-dependent malic enzyme in the supernatant and to some degree in the mitochondria; and pyruvate; orthophosphate dikinase in the chloroplasts. The activity of the NAD-dependent malate dehydrogenase was due to three isoenzymes separated by (NH4)2SO4 gradient solubilization. These isoenzymes represented 17, 78, and 5% of the activity recovered, respectively, in the order of elution. The isoenzyme eluting first was associated with the mitochondria and the second isoenzyme was of cytosolic origin, while the intracellular location of the third isoenzyme was probably the peroxisome. Based on these findings, the metabolic path of Crassulacean acid metabolism within cells of CAM plants is discussed.
New address: Institut für Pflanzenphysiologie und Zellbiologie, Freie Universität Berlin, Königin-Luise-Straße 12-16a. D-1000 Berlin 33 相似文献
2.
Diurnal changes in nitrogen assimilation of tobacco roots. 总被引:6,自引:0,他引:6
To gain an insight into the diurnal changes of nitrogen assimilation in roots the in vitro activities of cytosolic and plasma membrane-bound nitrate reductase (EC 1.6.6.1), nitrite reductase (EC 1.7.7.1) and cytosolic and plastidic glutamine synthetase (EC 6.3.1.2) were studied. Simultaneously, changes in the contents of total protein, nitrate, nitrite, and ammonium were followed. Roots of intact tobacco plants (Nicotiana tabacum cv. Samsun) were extracted every 3 h during a diurnal cycle. Nitrate reductase, nitrite reductase and glutamine synthetase were active throughout the day-night cycle. Two temporarily distinct peaks of nitrate reductase were detected: during the day a peak of soluble nitrate reductase in the cytosol, in the dark phase a peak of plasma membrane-bound nitrate reductase in the apoplast. The total activities of nitrate reduction were similar by day and night. High activities of nitrite reductase prevented the accumulation of toxic amounts of nitrite throughout the entire diurnal cycle. The resulting ammonium was assimilated by cytosolic glutamine synthetase whose two activity peaks, one in the light period and one in the dark, closely followed those of nitrate reductase. The contribution of plastidic glutamine synthetase was negligible. These results strongly indicate that nitrate assimilation in roots takes place at similar rates day and night and is thus differently regulated from that in leaves. 相似文献
3.
4.
Intracellular distribution of enzymes associated with nitrogen assimilation in roots 总被引:3,自引:0,他引:3
The cellular distribution of enzymes involved in nitrogen assimilation: nitrate reductase (EC 1.6.6.2), nitrite reductase (EC 1.6.6.4), glutamine synthetase (EC 6.3.1.2), glutamate synthase (EC 2.6.1.53), and glutamate dehydrogenase (EC 1.4.1.3) has been studied in the roots of five plants: maize (Zea mays L. hybrid W 64A x W 182E), rice (Oryza sativa L. cv. Delta), bean (Phaseolus vulgaris L. cv. Contender), pea (Pisum sativum L. cv. Demi-nain), and barley (Hordeum vulgare L.). Initially, cell organelles were separated from soluble proteins by differential centrifugation. Cell organelles were also subjected to sucrose density gradients. The results obtained by these two methods indicate that nitrite reductase and glutamate synthase are localized in plastids, nitrate reductase and glutamine synthetase are present in the cytosol, and glutamate dehydrogenase is a mitochondrial enzyme. 相似文献
5.
Ewa Gajewska Ewa Niewiadomska Krzysztof Tokarz Mirosława Słaba Maria Skłodowska 《Journal of plant physiology》2013
In this study, we analyzed the toxic effect of Ni during the development of wheat shoots. Typical developmental alterations in carbon metabolism-related parameters reflecting changes associated with the transition of the seedlings from heterotrophic to autotrophic metabolism were observed in the control shoots between the 1st and the 4th days. Adverse effects of 50 and 100 μM Ni became evident starting from the 4th day of growth on the metal-containing media. We found that Ni-induced stimulation of phosphoenolpyruvate carboxylase (PEPC) activity coincided with decrease in the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) level and with declines in net photosynthetic rate (PN) and stomatal conductance (gs). Application of Ni resulted in increased activities of several dehydrogenases: glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), isocitrate dehydrogenase (NADP-ICDH) and malate dehydrogenase (NADH-MDH). In contrast, the activities of malic enzymes (NADP-ME and NAD-ME) decreased due to Ni stress. Treatment with Ni led to accumulation of glucose and declined concentration of sucrose as well as considerable increases in concentrations of malic and citric acids. Our results indicate that Ni stress redirects the carbon metabolism of developing wheat shoots to provide carbon skeletons for synthesis of amino acids and organic acids as well as to supply reducing power to sustain normal metabolic processes and to support defense mechanisms against oxidative stress. 相似文献
6.
Gas and ion exchanges in wheat roots after nitrogen supply 总被引:5,自引:0,他引:5
Wheat (Triticum aestivum L. cv. Sicco) was grown for 10 days on CaSO4 (0.5 mmol dm?3) and then exposed for 2 days to various nitrogenous salts in an apparatus designed to measure the exchange of O2 and CO2, at constant pH and pNO3. Nitrate salts (KNO3 at 0.5 and Ca(NO3)2 at 0.25 and 1 mmol dm?3) caused a transient increase (40–50%) in both O2uptake and CO2 release by the roots. The rate of gas exchange was nearly doubled by (NH4)2SO4 (0.25 mmol dm?3). Respiration was constant in roots kept on CaSO4 or given KCl. In CaSO4 the content of water-soluble sugars in roots fell by about 15% day?1. The pletion of soluble sugars was higher with NO3? and NH4+(40 and 30% day?1, respectively). At most 10 to 20% of the released CO2 is involved in HCO3N?NO3? exchange and this fraction represents at most 10% of the total carbon imported or 30% of the net carbon gain by the roots. The contribution of the non-phosphorylating “alternative” route to total root respiration was 15% in CaSO4and over 40% with NH4+ In NO3? the roots respired exclusively via the cytochrome route. Increased respiration at decreased efficiency in roots of NH4+plants may be due to an overproduction of NADH. Our data support the contention that excess NADH as a “by-product” of the formation of carboxylates in the citrate cycle can be disposed of in an alternative respiratory pathway during NH4+nutrition. 相似文献
7.
Pathways of assimilation and transfer of fixed nitrogen in coralloid roots of cycad-Nostoc symbioses
Freshly detached coralloid roots of several cycad species were found to bleed spontaneously from xylem, permitting identification of products of nitrogen transfer from symbiotic organ to host. Structural features relevant to the export of fixed N were described for Macrozamia riedlei (Fisch. ex Gaud.) Gardn. the principal species studied. Citrulline (Cit), glutamine (Gln) and glutamic acid (Glu), the latter usually in a lesser amount, were the principal translocated solutes in Macrozamia (5 spp.), Encephalartos (4 spp.) and Lepidozamia (1 sp.), while Gln and a smaller amount of Glu, but no Cit were present in xylem sap of Bowenia (1 sp.),and Cycas (2 spp.). Time-course studies of 15N enrichment of the different tissue zones and the xylem sap of 15N2-pulse-fed coralloid roots of M. riedlei showed earlier 15N incorporation into Gln than into Cit, and a subsequent net decline in the 15N of Gln of the coralloid-root tissues, whereas Cit labeling continued to increase in inner cortex and stele and in the xylem sap. Hydrolysis of the 15N-labeled Cit and Gln consistently demonstrated much more intense labeling of the respective carbamyl and amide groups than of the other N-atoms. Coralloid roots of M. riedlei pulse-fed 14CO2 in darkness showed 14C labeling of aspartic acid (Asp) and Cit in all tissue zones and of Cit of xylem bleeding sap. Lateral roots and uninfected apogeotropic roots of M. riedlei and M. moorei also incorporated 14CO2 into Cit. The 14C of Cit was restricted to the carbamyl-C. Comparable 15N2 and CO2-feeding studies on corallid roots of Cycas revoluta showed Gln to be the dominant product of N2 fixation, with Asp and alanine as other major 14C-labeled amino compounds, but a total absence of Cit in labeled or unlabeled form.Abbreviations Ala
alanine
- Asp
aspartic acid
- Cit
citrulline
- Gln
glutamine
- Glu
glutamic acid
- Orn
ornithine 相似文献
8.
The effects of nitrate on the enzymes involved in nitrogen assimilation in nodulated pea roots 总被引:1,自引:0,他引:1
Pea Plants ( Pisum sativaum L. ev. Little Marvel) were grown in N-free medium and when well nodulated (28 days) were supplied for 8 days with nitrate or ammonium. Over the 8 days of nitrate treatment, total amino and amide N in sap declined, and the proportion of aspartate relative to the other amino acids increased. After 8 days of treatment, nitrogenase (EC 1.18.2.1) activity in nitrate-treated plants declined to about 30% of the activity in controls even though nodules were not directly in contact with nutrient solution. Nitrogenase activity was also decreased by the addition of ammonium chloride (10 m M ). With addition of nitrate or ammonium. clear signs of senescence began to show in the nodules after 4 days. Nitrate reductase (EC 1.6.6.1) activity was induced in roots by nitrate, but decreased sharply in nodules. In response to nitrate addition, newly formed root tissues showed 3- to 5-times higher glutamine synthetase (GS. EC 6.3.1.4) activity than newly formed tissues of control plants, expressed on a protein or weight basis. In complementary experiments, when ammonium salts were used instead of nitrates, the increase in GS activity was significantly lower. GS activity decreased in nodules of treated plants and total extractable protein was 3 times lower in nodules of nitrate-treated plants than in controls at day 8 of treatment. 相似文献
9.
10.
Summary Nitrate fertiliser labelled with15N was applied to a field grown crop of winter wheat. Uptake and assimilation of fertiliser nitrate was studied by monitoring the appearance of labelled nitrate and labelled amino acids in the xylem sap. Shortly after applying15N-nitrate to the soil about 30 per cent of recently absorbed15N was in the reduced form, indicating that roots of cereal crops can make a substantial contribution in reducing nitrate. Seasonal changes in crop growth andin vivo NRA are also described. 相似文献
11.
为了解小麦花后介质氮素输入籽粒的同化途径,在不同发育时期不同施氮水平下,采用GS抑制剂(草丁膦)和15N示踪结合,研究了高低籽粒蛋白两种类型品种花后介质氮素的同化特征.结果表明,叶片GS抑制剂处理使豫麦47穗中的NDFF(氮含量中来自介质N的百分比)显著升高,豫麦50则显著降低;穗部GS抑制剂处理使豫麦47叶中的NDFF上升,而豫麦50(开花期)低氮处理上升、高氮处理下降.花后豫麦47的介质N同化量远大于豫麦50,同化介质N的主要器官为根茎,根茎∶叶∶穗的花后介质氮同化量之比约为4∶1∶2;而豫麦50的主要同化器官则为叶片,根茎∶叶∶穗之比约为1∶5∶1.随施N量的增加,豫麦47叶片花后介质N同化量增加,豫麦50则减少;且豫麦47叶片花后同化介质N的输出量显著小于籽粒花后介质N的同化量,而豫麦50叶片花后介质氮的输出量显著大于籽粒介质N的同化量.说明不同类型小麦品种花后N素由根系到籽粒的代谢同化途径具有显著差异,高蛋白品种豫麦47花后由根系流向籽粒的氮素可以不经叶片直接到达籽粒,低蛋白品种豫麦50则必须经过叶片才能到达籽粒. 相似文献
12.
Acquisition and assimilation of nitrogen as peptide-bound and D-enantiomers of amino acids by wheat 总被引:1,自引:0,他引:1
Hill PW Quilliam RS DeLuca TH Farrar J Farrell M Roberts P Newsham KK Hopkins DW Bardgett RD Jones DL 《PloS one》2011,6(4):e19220
Nitrogen is a key regulator of primary productivity in many terrestrial ecosystems. Historically, only inorganic N (NH(4)(+) and NO(3)(-)) and L-amino acids have been considered to be important to the N nutrition of terrestrial plants. However, amino acids are also present in soil as small peptides and in D-enantiomeric form. We compared the uptake and assimilation of N as free amino acid and short homopeptide in both L- and D-enantiomeric forms. Sterile roots of wheat (Triticum aestivum L.) plants were exposed to solutions containing either (14)C-labelled L-alanine, D-alanine, L-trialanine or D-trialanine at a concentration likely to be found in soil solution (10 μM). Over 5 h, plants took up L-alanine, D-alanine and L-trialanine at rates of 0.9±0.3, 0.3±0.06 and 0.3±0.04 μmol g(-1) root DW h(-1), respectively. The rate of N uptake as L-trialanine was the same as that as L-alanine. Plants lost ca.60% of amino acid C taken up in respiration, regardless of the enantiomeric form, but more (ca.80%) of the L-trialanine C than amino acid C was respired. When supplied in solutions of mixed N form, N uptake as D-alanine was ca.5-fold faster than as NO(3)(-), but slower than as L-alanine, L-trialanine and NH(4)(+). Plants showed a limited capacity to take up D-trialanine (0.04±0.03 μmol g(-1) root DW h(-1)), but did not appear to be able to metabolise it. We conclude that wheat is able to utilise L-peptide and D-amino acid N at rates comparable to those of N forms of acknowledged importance, namely L-amino acids and inorganic N. This is true even when solutes are supplied at realistic soil concentrations and when other forms of N are available. We suggest that it may be necessary to reconsider which forms of soil N are important in the terrestrial N cycle. 相似文献
13.
Inorganic nitrogen is an essential nutrient for photosynthetic organisms. Its efficient use in nature involves adaptation of the organisms to the availability of the nitrogen supply, to changing environmental conditions, and to the provision of carbon and other nutrients. The unicellular alga Chlamydomonas provides a useful model to identify not only each of the components participating in the assimilative process in a species, but also the regulatory networks modulating their activity. A remarkable fact is the ample array of transporters for inorganic nitrogen compounds operating in this single cell: 13 putative nitrate/nitrite transporters and eight putative ammonium transporters. However, for nitrate, only a few of them participate as the main suppliers of nitrogen for cell growth, and others probably function to adapt nitrogen utilization efficiency to conditions depending not only on the nitrogen source available but also on other nutrients and environmental conditions. This paper summarizes recent findings in Chlamydomonas to provide an integrated perspective. 相似文献
14.
Thomas Larsen Antonie Gorissen Paul Henning Krogh Marc Ventura Jakob Magid 《Plant and Soil》2007,295(1-2):253-264
It has been demonstrated that plant roots can take up small amounts of low-molecular weight (LMW) compounds from the surrounding
soil. Root uptake of LMW compounds have been investigated by applying isotopically labelled sugars or amino acids but not
labelled organic matter. We tested whether wheat roots took up LMW compounds released from dual-labelled (13C and 15N) green manure by analysing for excess 13C in roots. To estimate the fraction of green manure C that potentially was available for root uptake, excess 13C and 15N in the primary decomposers was estimated by analysing soil dwelling Collembola that primarily feed on fungi or microfauna.
The experimental setup consisted of soil microcosm with wheat and dual-labelled green manure additions. Plant growth, plant
N and recoveries of 13C and 15N in soil, roots, shoots and Collembola were measured at 27, 56 and 84 days. We found a small (<1%) but significant uptake
of green manure derived 13C in roots at the first but not the two last samplings. About 50% of green manure C was not recovered from the soil-plant
system at 27 days and additional 8% was not recovered at 84 days. Up to 23% of C in collembolans derived from the green manure
at 56 days (the 27 days sampling was lost). Using a linear mixing model we estimated that roots or root effluxes provided
the main C source for collembolans (54−79%). We conclude that there is no solid support for claiming that roots assimilated
green manure derived C due to very small or no recoveries of excess 13C in wheat roots. During the incubation the pool of green manure derived C available for root uptake decreased due to decomposition.
However, the isotopic composition in Collembola indicated that there was a considerable fraction of green manure derived C
in the decomposer system at 56 days thus supporting the premise that LMW compounds containing C from the green manure was
released throughout the incubation.
Responsible Editor: A. C. Borstlap. 相似文献
15.
16.
17.
Although nutrient stress is known to alter partitioning between shoots and roots, the physiological basis for the phenomenon is unresolved. Experiments were conducted to examine assimilation of 15NO3 by N-stressed plants and to determine whether apparent changes in assimilation in the root contributed to alterations in whole-plant partitioning of reduced-N. Tobacco plants (Nicotiana tabacum L. cv. NC 2326) were exposed to a low concentration of NO3? in solution (80 μM) for 9 days to effect a N-stress response. Exposure of plants to 1000 μM15NO3? for 12 h on selected days revealed that roots of N-stressed plants developed an increased capacity to absorb NO3?, and accumulation of reduced-15N in the root increased to an even greater extent. When plants were exposed to 80 or 1000 μM15NO3? in steady-state, 15NO3? uptake over a 12 h period was noticeably restricted at the lower concentration, but a larger proportion of the absorbed 15N still accumulated as reduced-15N in the root. The alteration in reduced-15N partitioning was maintained in N-stressed plants during the subsequent 3-day “chase” period when formation of insoluble reduced-15N in the root was quantitatively related to the disappearance of 15NO3? and soluble reduced-15N. The results indicate that increased assimilation of absorbed NO3?, in the root may contribute significantly to the altered reduced-N partitioning which occurs in N-stressed plants. 相似文献
18.
The mechanisms of nitrogen assimilation in Pseudomonads 总被引:1,自引:0,他引:1
Pseudomonas aeruginosa, Ps. fluorescens and 3 marine psychrophylic pseudomonads were grown in chemostat cultures with nitrate ammonia or glutamate as nitrogen source.
In cultures grown on nitrate (either carbon- or nitrogen-limited) and in ammonia nitrogen-limited cultures ammonia was assimilated
via the GS/GOGAT pathway. With a excess of ammonia in the culture however ammonia was assimilated via GDH and GS was either
present only at low levels or absent. Two distinct GDH activities were detected in all 5 bacteria, one specific to NAD and
one to NADP. The presence of these activities was determined by the environment in which cells were grown. These activities
showed differences with respect to substrate affinity (Km values) for ammonia, incubation temperature and to a lesser extent
pH and may involve separate GDH isoenzymes. GS from the marine bacterium PL1 had a very high affinity for ammonia (Km of 0.3mm) but a low affinity for glutamate (Km of 19mm). 相似文献
19.
Aspects of inorganic nitrogen assimilation in yeasts 总被引:1,自引:0,他引:1
Cultures of Candida utilis utilise glutamate in preference to ammonia and ammonia in preference to nitrate. The nitrate reductase of this organism is induced by nitrate and repressed in cultures grown on glutamate or ammonia. Nitrate-grown cultures of C. utilis, irrespective of the medium nitrate concentration, behave as though nitrogen-limited. In contrast to C. utilis, Saccharomyces cerevisiae utilises ammonia in preference to glutamate. In eight yeasts studied the highest cellular contents of biosynthetic NADP-linked glutamate dehydrogenase were found in batch cultures containing low concentrations of ammonia or in nitrogen-limited chemostat cultures. NAD-linked glutamate dehydrogenase activity was detected in extracts of cells grown in the presence of glutamate but not in those grown in the presence of ammonia. 相似文献
20.
The effect of the source of inorganic nitrogen on growth and enzymes of nitrogen assimilation in soybean and wheat cells in suspension cultures 总被引:1,自引:0,他引:1
Summary Soybean (Glycine max L. cv. Mandarin) and wheat (Triticum monococcum L.) cells were grown in media with NO3
- plus NH4
+ (B5) and NO3
- without NH4
+ (B5-NH4) as nitrogen sources. Changes in pH, [NO3
-] and [NH4
+] in media, and dry weight, protein content, nitrate reductase (NR) and glutamate dehydrogenase (GDH) in the cells were followed for about 170 h. With both NH4
+ and NO3
- in the medium, NH4
+ was utilized very quickly. Soybean cells grew poorly in the absence of NH4
+ while wheat cells grew equally well on media with or without NH4
+. When soybean cells were grown in medium with NO3
- plus NH4
+, dry weight and NR activity remained relatively low for several hours after which both increased rapidly. This coincided with the time NH4
+ was depleted from the medium. In the absence of NH4
+, soybean cell growth and NR activity remained low. NR activity in wheat cells, and GDH activity in soybean and wheat cells, did not vary significantly in the presence or absence of NH4
+.This work was supported by a grant in aid of research from the National Research Council of Canada to one of us (J. K.). NRCC No. 12521. 相似文献