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1.
Phosphite (H2PO3–, Phi) prevents the acclimation of plants and yeast to orthophosphate (Pi, HPO42–) deprivation by specifically obstructing the derepression of genes encoding proteins characteristic of their Pi-starvation response. In this study, we report that prolonged (i.e., 3–4 weeks) culture of Brassica napus L. suspension cells in Pi-deficient (–Pi) media leads to programmed cell death (PCD). However, when the B. napus cells were subcultured into –Pi media containing 2 mM Phi, they initiated PCD within 5 days, with 95% cell death observed by day 9. Dying cells exhibited several morphological and biochemical features characteristic of PCD, including protoplast shrinkage, chromatin condensation, and fragmentation of nuclear DNA. Immunoblotting indicated that B. napus cells undergoing PCD upregulated a 30-kDa cysteine endoprotease that is induced during PCD in the inner integument cells of developing B. napus seeds. It is concluded that PCD in B. napus suspension cells is triggered by extended Pi starvation, and that Phi treatment greatly accelerates this process. Our results also infer that the adaptive value of acclimating at the molecular level to Pi-stress is to extend the viability of –Pi B. napus cell cultures by about 3 weeks.Abbreviations APase acid phosphatase (EC 3.1.3.2) - BnCysP B. napus cysteine proteinase - DAPI 4,6-diamidino-2-phenylindole - FDA fluorescein diacetate - PCD programmed cell death - Phi phosphite - +Pi and –Pi Pi-sufficient and -deficient, respectively - PI propidium iodide - PSI Pi-starvation inducible 相似文献
2.
Induction of PPi-dependent phosphofructokinase by phosphate starvation in seedlings of Brassica nigra 总被引:1,自引:0,他引:1
Activity of PPi-dependent phosphofructokinase (PFP) was monitored in Brassica nigra seedlings grown under nutrient-sufficient or phosphate (Pi)-starved conditions. Roots, stems and leaves of 50 d Pi-deficient seedlings displayed 4.0-, 3.7- and 2.3-fold greater PFP activity, respectively, than did nutrient sufficient controls. This induction was based primarily upon an increased susceptibility of PFP from the Pi-starved tissues to activation by fructose-2,6-bisphosphate. The ratio of PFP to ATP-dependent phosphofructokinase (PFK) was approximately 2:1 and 1:1 in the various organs of 50 d Pi-starved and Pi-fed plants, respectively. Immunoblots probed with anti-(potato PFP) immune serum revealed that the induction of PFP in Pi-starved B. nigra was coincident with an elevation in the amount of PFP α-subunit in the leaves as well as an increase in the α:β subunit ratio in the stems and roots. Induction of PFP in the various tissues was also accompanied by an appreciable decline in intracellular Pi level, decreased soluble protein content, and elevated phosphoenolpyruvate phosphatase activity. Time course studies revealed that these responses to Pi stress were significantly delayed in the leaves as compared to the roots and stems suggesting that Pi may be preferentially sequestered to the leaves during Pi starvation. These data also provide further evidence that B. nigra PFP is an adaptive enzyme that may function during Pi deprivation as: (1) a glycolytic bypass to PFK; and (2) a ‘Pi-recycling system’ that converts esterified-P to Pi that would be rapidly reassimilated into the metabolism of the Pi-deficient cells. 相似文献
3.
A major problem in defining the physiological role of pyrophosphate:fructose 6-phosphate 1-phosphotransferase (PFP, EC 2.7.1.90)
is the 1,000-fold discrepancy between the apparent affinity of PFP for its activator, fructose 2,6-bisphosphate (Fru-2,6-P2), determined under optimum conditions in vitro and the estimated concentration of this signal metabolite in vivo. The aim
of this study was to investigate the combined influence of metabolic intermediates and inorganic phosphate (Pi) on the activation
of PFP by Fru-2,6-P2. The enzyme was purified to near-homogeneity from leaves of spinach (Spinacia oleracea L.). Under optimal in vitro assay conditions, the activation constant (K
a) of spinach leaf PFP for Fru-2,6-P2 in the glycolytic direction was 15.8 nM. However, in the presence of physiological concentrations of fructose 6-phosphate,
inorganic pyrophosphate (PPi), 3-phosphoglycerate (3PGA), phosphoenolpyruvate (PEP), ATP and Pi the K
a of spinach leaf PFP for Fru-2,6-P2 was up to 2000-fold greater than that measured in the optimised assay and V
max decreased by up to 62%. Similar effects were observed with PFP purified from potato (Solanum tuberosum L.) tubers. Cytosolic metabolites and Pi also influenced the response of PFP to activation by its substrate fructose 1,6-bisphosphate
(Fru-1,6-P2). When assayed under optimum conditions in the gluconeogenic direction, the K
a of spinach leaf PFP for Fru-1,6-P2 was approximately 50 μM. Physiological concentrations of PPi, 3PGA, PEP, ATP and Pi increased K
a up to 25-fold, and decreased V
max by over 65%. From these results it was concluded that physiological concentrations of metabolites and Pi increase the K
a of PFP for Fru-2,6-P2 to values approaching the concentration of the activator in vivo. Hence, measured changes in cytosolic Fru-2,6-P2 levels could appreciably alter the activation state of PFP in vivo. Moreover, the same levels of metabolites increase the
K
a of PFP for Fru-1,6-P2 to an extent that activation of PFP by this compound is unlikely to be physiologically relevant.
Received: 21 July 2000 / Accepted: 15 September 2000 相似文献
4.
Effects of phosphite (Phi) on phosphate (Pi) starvation responses were determined in Ulva lactuca L. by incubation in Pi‐limited (1 μM NaH2PO4) or Pi‐sufficient (100 μM NaH2PO4) seawater containing 0–3 mM Phi. Exposure to 1 μM NaH2PO4 decreased the growth rate and the content of free Pi and esterified‐P but increased the activities of extracellular alkaline phosphatase (EC 3.1.2.1) and intracellular acid phosphatase (ACP; EC 3.1.2.2); two ACP isozymes observed by activity staining on isoelectric focussing (IEF) gel were induced. The Km value of Pi uptake rate was decreased by incubation with 1 μM NaH2PO4 and the decrease in Km value was inhibited by 2 mM Phi, reflecting the operation of a high‐affinity Pi uptake system at low Pi concentrations. In the presence of Phi, the growth rate of Pi‐sufficient and Pi‐starved thalli decreased as Phi concentrations were increased from 0 to 2 mM. As Phi concentrations were increased from 0 to 2 mM, the free Pi contents in both Pi‐sufficient and Pi‐starved thalli decreased, but the esterified‐P contents in Pi‐starved thalli increased, whereas those in Pi‐sufficient thalli increased at 1 mM Phi and decreased at 2 mM Phi. Cell wall localized AP activity in both Pi‐sufficient and Pi‐starved thalli decreased as Phi concentrations were increased from 0 to 2 mM. Intracellular ACP activity in Pi‐starved thalli decreased as Phi concentrations were increased from 0 to 2 mM but was not affected in Pi‐sufficient thalli. The induction of ACP isozyme activity and high‐affinity Pi uptake system in Pi‐starved thalli was inhibited by Phi. The present investigation shows that Phi interrupts the sensing mechanisms of U. lactuca to Pi‐limiting conditions. 相似文献
5.
The Fungicide Phosphonate Disrupts the Phosphate-Starvation Response in Brassica nigra Seedlings 总被引:6,自引:0,他引:6
The development of Brassica nigra seedlings over 20 d of growth was disrupted by the fungicide phosphonate (Phi) in a manner inversely correlated with nutritional inorganic phosphate (Pi) levels. The growth of Pi-sufficient (1.25 mM Pi) seedlings was suppressed when 10, but not 5, mM Phi was added to the nutrient medium. In contrast, the fresh weights and root:shoot ratios of Pi-limited (0.15 mM) seedlings were significantly reduced at 1.5 mM Phi, and they progressively declined to about 40% of control values as medium Phi concentration was increased to 10 mM. Intracellular Pi levels generally decreased in Phi-treated seedlings, and Phi accumulated in leaves and roots to levels up to 6- and 16-fold that of Pi in Pi-sufficient and Pi-limited plants, respectively. Extractable activities of the Pi-starvation-inducible enzymes phosphoenolpyruvate phosphatase and inorganic pyrophosphate-dependent phosphofructokinase were unaltered in Pi-sufficient seedlings grown on 5 or 10 mM Phi. However, when Pi-limited seedlings were grown on 1.5 to 10 mM Phi (a) the induction of phosphoenolpyruvate phosphatase and inorganic pyrophosphate-dependent phosphofructokinase activities by Pi limitation was reduced by 40 to 90%, whereas (b) soluble protein concentrations and the activities of the ATP-dependent phosphofructokinase and pyruvate kinase were unaffacted. It is concluded that Phi specifically interrupts processes involved in regulation of the Pi-starvation response in B. nigra. 相似文献
6.
Julie Misson Pascale Henner Marcel Morello Magali Floriani Ting-Di Wu Jean-Luc Guerquin-Kern Laureline Fvrier 《Environmental and Experimental Botany》2009,67(2):353-362
Uranium is an ubiquitous pollutant with known chemical and radiological toxicity, which is naturally present in the plant environment. Due to its high affinity for phosphate, insoluble uranium-phosphate precipitates are formed in soils as well as in contaminated plant cells. To date, consequences of such interactions on uranium toxicity and on phosphate availability and metabolism in plants are unknown. This study aims at evaluating in which extent uranium-phosphate interactions have an effect on physiological and molecular mechanisms involved in plant responses (i) to uranium contamination and (ii) to phosphate availability in Arabidopsis thaliana.Inorganic phosphate (Pi) supply in U-contaminated medium was shown to decrease U bioaccumulation and U toxic effects on plant biomass and root cell viability. Besides, U was shown to disturb plant responses to Pi availability. Indeed, in Pi-sufficient conditions, high U concentrations promoted the induction of phosphate starvation responses in plants. However, the most drastic effects have been observed in Pi-deficient conditions as U affected the following plant responses to Pi-starvation: root architecture modulation, phosphate acquisition and optimization of phosphate allocation. Indeed, despite the low Pi status of these plants, 2 μM U inhibited the primary root growth arrest normally triggered by low Pi. Moreover, Pi uptake and translocation to shoot were reduced. The root concentration of soluble inorganic phosphate decreased in Pi-starved plantlets contaminated with U, despite the enhancement of shoot-to-root remobilization of Pi. The observations of intracellular and apoplastic deposits of U and P in roots using electron microscopy (TEM-EDX) and secondary ion mass spectroscopy (NanoSIMS) provided evidence that Pi flux disturbance is a consequence of the use of Pi to immobilize U within roots. 相似文献
7.
Suren Deng Jingyi Li Zezhen Du Zixuan Wu Jian Yang Hongmei Cai Gaobing Wu Fangsen Xu Yichao Huang Sheliang Wang Chuang Wang 《Plant, cell & environment》2022,45(1):191-205
The concentration and homeostasis of intracellular phosphate (Pi) are crucial for sustaining cell metabolism and growth. During short-term Pi starvation, intracellular Pi is maintained relatively constant at the expense of vacuolar Pi. After the vacuolar stored Pi is exhausted, the plant cells induce the synthesis of intracellular acid phosphatase (APase) to recycle Pi from expendable organic phosphate (Po). In this study, the expression, enzymatic activity and subcellular localization of ACID PHOSPHATASE 1 (OsACP1) were determined. OsACP1 expression is specifically induced in almost all cell types of leaves and roots under Pi stress conditions. OsACP1 encodes an acid phosphatase with broad Po substrates and localizes in the endoplasmic reticulum (ER) and Golgi apparatus (GA). The phylogenic analysis demonstrates that OsACP1 has a similar structure with human acid phosphatase PHOSPHO1. Overexpression or mutation of OsACP1 affected Po degradation and utilization, which further influenced plant growth and productivity under both Pi-sufficient and Pi-deficient conditions. Moreover, overexpression of OsACP1 significantly affected intracellular Pi homeostasis and Pi starvation signalling. We concluded that OsACP1 is an active acid phosphatase that regulates rice growth under Pi stress conditions by recycling Pi from Po in the ER and GA. 相似文献
8.
K. Nakamura M. A. Yudiarto N. Kaneko H. Kurosawa Y. Amano 《Applied microbiology and biotechnology》1997,48(6):753-757
A microbial method to determine sulphate concentration in water was developed on the basis of sulphate-dependent acid phosphatase
(APase) in whole cells of Thiobacillus thiooxidans. The activity of the APase was determined colorimetrically by using p-nitrophenylphosphate as substrate. The APase was activated by sulphate. A linear relationship was obtained between the activity
of the APase and the concentration of sulphate in the range 0–0.6 mM. Therefore, the sulphate concentration was estimated
from the APase activity, represented by the absorbance (A
400). The microbial method was applied to the determination sulphate in water. The lower limit of detection was 0.02 mM, the
relative standard deviation being 2% for 10 measurements on a standard sample. As for practical samples, which were taken
from rain, river and tap water, good agreement was obtained between the values measured by the microbial method and those
given by a conventional barium chloranilate method. The relative standard deviation was 2.1% for 12 measurements of tap water.
The activity of the APase was stable over a period of more than 100 days when the cells were stored in 0.1 M sodium acetate/acetic
acid buffer (pH 5.0) at 4 °C.
Received: 21 March 1997 / Received revision: 30 June 1997 / Accepted: 27 July 1997 相似文献
9.
Previously, we reported that phosphate (Pi) starvation of suspension cells or seedlings of Brassica nigra results in a large elevation in the activity of pyrophosphate-dependent phosphofructokinase (EC 2.7.1.90) (PFP). However, other researchers have found that Pi deprivation either causes a significant reduction or no change in extractable PFP activity of Catharanthus roseus suspension cells, or roots of Nicotiana tabacum and Phaseolis vulgaris seedlings. The present study was undertaken to examine the prevalence of Pi starvation-inducible PFP in seedlings, root cultures, or suspension cells of a variety of plant species differing in phylogenetic relatedness to B. nigra. In all species examined, fresh weights were decreased and acid phosphatase (EC 3.1.3.2) activities were increased by Pi limitation. Brassica napus suspension cells, Arabidopsis thaliana seedlings, and roots of B. napus, B. carinata, B. oleracea, Beta vulgaris, Fagopyrum esculentum, Sinapis alba, and S. arvensis seedlings grown with Pi-limited media contained 170–510% greater PFP activity than did nutrient-sufficient controls. In five of these species the induction of PFP activity by Pi limitation was based in part upon an increased susceptibility of the enzyme to its allosteric activator, fructose-2,6-bisphosphate. By contrast, the PFP activity in Pi-deprived Lycopersicon esculentum root cultures and Nicotiana silvestris suspension cells decreased by 45–65% relative to Pi-sufficient controls. Immunoblotting of extracts from A. thaliana seedlings, S. arvensis, F. esculentum and B. oleracea roots, and B. napus suspension cells probed with potato tuber PFP antibodies indicated that the upregulation of PFP activity by Pi stress in these species was not correlated with an alteration in the amount or subunit composition of PFP. Our findings suggest that induction of PFP during long-term Pi starvation may be characteristic of members of the Cruciferae, Chenopodiaceae and Polygonaceae families whose roots do not form symbiotic associations with mycorrhizal fungi. 相似文献
10.
11.
12.
Functional analysis and cell-specific expression of a phosphate transporter from tomato 总被引:28,自引:0,他引:28
Pierre Daram Silvia Brunner Bengt L. Persson Nikolaus Amrhein Marcel Bucher 《Planta》1998,206(2):225-233
13.
Induction and secretion of acid phosphatases (APases) is thought to be an adaptive mechanism that helps plants survive and grow under phosphate (Pi) deprivation, in Arabidopsis, there are 29 purple acid phosphatase (AtPAP) genes. To systematically investigate the roles of different AtPAPs, we first identified knockout or knock-down T-DNA lines for all 29 AtPAP genes. Using these atpap mutants combined with in-gel and quantitative APase enzyme assays, we demonstrated that AtPAP12 and AtPAP26 are two major intracellular and secreted APases in Arabidopsis while AtPAPlo is mainly a secreted APase. On Pi-deficient (P-) medium or P- medium supplemented with the organophosphates ADP and fructose-6-phosphate (Fru-6-P), growth of atpaplo was significantly reduced whereas growth of atpap12 was only moderately reduced, and growth of atpap26 was nearly equal to that of the wild type (WT). Overexpression of the AtPAP12 or AtPAP26 gene, however, caused plants to grow better on P- or P- medium supplemented with ADP or Fru-6-P. Interest-ingly, Pi levels are essentially the same for the WT and overexpressing lines, although these two types of plants have significantly different growth phenotypes. These results suggest that the APases may have other roles besides enhancing internal Pi recycling or releasing Pi from external organophosphates for plant uptake. 相似文献
14.
Purification and characterization of pyrophosphate-dependent phosphofructokinase from phosphate-starved Brassica nigra suspension cells. 下载免费PDF全文
Previously, we reported that inorganic phosphate (Pi) deprivation of Brassica nigra suspension cells or seedlings leads to a progressive increase in the alpha: beta-subunit ratio of the inorganic pyrophosphate (PPi)-dependent phosphofructokinase (PFP) and that this coincides with a marked enhancement in the enzyme's activity and sensitivity to its allosteric activator, fructose-2,6-bisphosphate (Fru-2,6-P2). To further investigate the effect of Pi nutrition on B. nigra PFP, the enzyme was purified and characterized from Pi-starved B. nigra suspension cell cultures. Polyacrylamide gel electrophoresis, immunoblot, and gel-filtration analyses of the final preparation indicated that this enzyme exists as a heterooctamer of approximately 500 kD and is composed of a 1:1 ratio of immunologically distinct alpha (66 kD) and beta (60 kD) subunits. The enzyme's alpha subunit was susceptible to partial proteolysis during purification, but this was prevented by the presence of chymostatin and leupeptin. In the presence and absence of 5 microM Fru-2,6-P2, the forward activity of PFP displayed pH optima of pH 6.8 and 7.6, respectively. Maximal activation of the forward and reverse reactions by Fru-2,6-P2 occurred at pH 6.8. The potent inhibition of the forward activity by Pi (concentration of inhibitor producing 50% inhibition of enzyme activity [I50] = 1.3 mM) was attributed to a marked Pi-dependent reduction in Fru-2,6-P2 binding. The reverse reaction was substrate-inhibited by Pi (I50 = 13 mM) and product-inhibited by PPi (I50 = 0.9 mM). The kinetic data are consistent with the hypothesis that PFP may function to bypass the ATP-dependent PFP in Pi-starved B. nigra. The importance of the Pi nutritional status to the regulation and predicted physiological function of PFP is emphasized. 相似文献
15.
E. Nádas Á. Balogh F. Kiss K. Szente Z. Nagy R. Martínez-Carrasco Z. Tuba 《Photosynthetica》2008,46(2):255-261
We studied the effects of 15-months of elevated (700 μmol mol−1) CO2 concentration (EC) on the CO2 assimilation rate, saccharide content, and the activity of key enzymes in the regulation of saccharide metabolism (glycolysis
and gluconeogenesis) of four C3 perennial temperate grassland species, the dicots Filipendula vulgaris and Salvia nemorosa and the monocots Festuca rupicola and Dactylis glomerata. The acclimation of photosynthesis to EC was downward in F. rupicola and D. glomerata whereas it was upward in F. vulgaris and S. nemorosa. At EC, F. rupicola and F. vulgaris leaves accumulated starch while soluble sugar contents were higher in F. vulgaris and D. glomerata. EC decreased pyrophosphate-D-fructose-6-phosphate l-phosphotransferase (PFP, EC 2.7.1.90) activity assayed with Fru-2,6-P2 in F. vulgaris and D. glomerata and increased it in F. rupicola and S. nemorosa. Growth in EC decreased phosphofructokinase (PFK, EC 2.7.1.11) activity in all four species, the decrease being smallest
in S. nemorosa and greatest in F. rupicola. With Fru-2,6-P2 in the assay medium, EC increased the PFP/PFK ratio, except in F. vulgaris. Cytosolic fructose-1,6-bisphosphatase (Fru-1,6-P2ase, EC 3.1.3.11) was inhibited by EC, the effect being greatest in F. vulgaris and smallest in F. rupicola. Glucose-6-phosphate dehydrogenase (G6PDH EC 1.1.1.49) activity was decreased by growth EC in the four species. Activity
ratios of Fru-1,6-P2ase to PFP and PFK suggest that EC may shift sugar metabolism towards glycolysis in the dicots. 相似文献
16.
Domingo Ruvalcaba-Ruíz Guadalupe Palomino Javier Martínez Ignacio Méndez Benjamín Rodríguez-Garay 《In vitro cellular & developmental biology. Plant》2012,48(1):144-152
The effect of para-fluorophenylalanine (PFP) on the production of trisomic plants of Agave tequilana Weber var. Azul produced through somatic embryogenesis was investigated. Normal diploid plants with 2n = 2x = 60 were obtained in the control treatment and with 4 mg L−1 PFP exposure, while use of 8 and 12 mg L−1 PFP led to production of trisomics with 2n = 2x = 61. Normal diploid plants showed a bimodal karyotype with five pairs of large chromosomes and 25 pairs of small chromosomes.
Trisomic plants also had a bimodal karyotype with a group of three chromosomes in position five of the chromosome set. More
than 13 homologous chromosome pairs exhibited structural changes. Differences in chromosome arm ratio (long arm/short arm)
were also found in eight chromosome pairs; all these aberrations in the chromosome complement of trisomic plants were probably
caused by inversions, deletions, and/or duplications produced by high concentrations of PFP. The gross chromosome structural
changes and the presence of a single extra chromosome could have been induced by the effect of PFP on the mitotic spindle
by inducing nondisjunction of sister chromatids, resulting in hyperploids (2n + x) and hypoploids (2n − x). Flow cytometric analysis of nuclear DNA content was performed using nuclei isolated from young leaves of normal and trisomic
plants. The 2C DNA content of 8.635 pg (1Cx = 4,223 Mbp of trisomic plants was different (p < 0.001) than that of normal plants (2C DNA = 8.389 pg (1Cx = 4,102 Mbp). The difference in genome size was correlated with the large structural changes in the trisomic plant genomes. 相似文献
17.
The morphological and physiological responses of barley to moderate Pi deficiency and the ability of barley to grow on phytate
were investigated. Barley cultivars (Hordeum vulgare L., Promyk, Skald and Stratus) were grown for 1–3 weeks on different nutrient media with contrasting phosphorus source: KH2PO4 (control), phytic acid (PA) and without phosphate (−P). The growth on −P medium strongly decreased Pi concentration in the
tissues; culture on PA medium generally had no effect on Pi level. Decreased content of Pi reduced shoot and root mass but
root elongation was not affected; Pi deficit had slightly greater impact on growth of barley cv. Promyk than other varieties.
Barley varieties cultured on PA medium showed similar growth to control. Extracellular acid phosphatase activities (APases)
in −P roots were similar to control, but in PA plants were lower. Histochemical visualization indicated for high APases activity
mainly in the vascular tissues of roots and in rhizodermis. Pi deficiency increased internal APase activities mainly in shoot
of barley cv. Stratus and roots of cv Promyk; growth on PA medium had no effect or decreased APase activity. Protein extracts
from roots and shoots were run on native discontinuous PAGE to determine which isoforms may be affected by Pi deficiency or
growth on PA medium; two of four isoforms in roots were strongly induced by conditions of Pi deficit, especially in barley
cv. Promyk. In conclusion, barley cultivars grew equally well both on medium with Pi and where the Pi was replaced with phytate
and only slightly differed in terms of acclimation to moderate deficiency of phosphate; they generally used similar pools
of acid phosphatases to acquire Pi from external or internal sources. 相似文献
18.
Nucleoside di- and triphosphates and adenosine regulate several components of the mucocilairy clearance process (MCC) that
protects the lung against infections, via activation of epithelial purinergic receptors. However, assessing the contribution
of individual nucleotides to MCC functions remains difficult due to the complexity of the mechanisms of nucleotide release
and metabolism. Enzymatic activities involved in the metabolism of extracellular nucleotides include ecto-ATPases and secreted
nucleoside diphosphokinase (NDPK) and adenyl kinase, but potent and selective inhibitors of these activities are sparse. In
the present study, we discovered that ebselen markedly reduced NDPK activity while having negligible effect on ecto-ATPase
and adenyl kinase activities. Addition of radiotracer [γ
32P]ATP to human bronchial epithelial (HBE) cells resulted in rapid and robust accumulation of [32P]-inorganic phosphate (32Pi). Inclusion of UDP in the incubation medium resulted in conversion of [γ
32P]ATP to [32P]UTP, while inclusion of AMP resulted in conversion of [γ
32P]ATP to [32P]ADP. Ebselen markedly reduced [32P]UTP formation but displayed negligible effect on 32Pi or [32P]ADP accumulations. Incubation of HBE cells with unlabeled UTP and ADP resulted in robust ebselen-sensitive formation of
ATP (IC50 = 6.9 ± 2 μM). This NDPK activity was largely recovered in HBE cell secretions and supernatants from lung epithelial A549
cells. Kinetic analysis of NDPK activity indicated that ebselen reduced the V
max of the reaction (K
i = 7.6 ± 3 μM), having negligible effect on K
M values. Our study demonstrates that ebselen is a potent non-competitive inhibitor of extracellular NDPK. 相似文献
19.
Physiological adaptations to phosphorus deficiency during proteoid root development in white lupin 总被引:33,自引:0,他引:33
Release of large amounts of citric acid from specialized root clusters (proteoid roots) of phosphorus (P)-deficient white
lupin (Lupinus albus L.) is an efficient strategy for chemical mobilization of sparingly available P sources in the rhizosphere. The present study
demonstrates that increased accumulation and exudation of citric acid and a concomitant release of protons were predominantly
restricted to mature root clusters in the later stages of P deficiency. Inhibition of citrate exudation by exogenous application
of anion-channel blockers such as ethacrynic- and anthracene-9-carboxylic acids may indicate involvement of an anion channel.
Phosphorus-deficiency-induced accumulation and subsequent exudation of citric acid seem to be a consequence of both increased
biosynthesis and reduced metabolization of citric acid in the proteoid root tissue, indicated by increased in-vitro activity and enzyme protein levels of phosphoenolpyruvate carboxylase (EC 4.1.1.31), and reduced activity of aconitase (EC
4.2.1.3) and root respiration. Similar to citric acid, acid phosphatase, which is secreted by roots and involved in the mobilization
of the organic soil P fraction, was released predominantly from proteoid roots of P-deficient plants. Also 33Pi uptake per unit root fresh-weight was increased by approximately 50% in juvenile and mature proteoid root clusters compared
to apical segments of non-proteoid roots. Kinetic studies revealed a K
m of 30.7 μM for Pi uptake of non-proteoid root apices in P-sufficient plants, versus K
m values of 8.5–8.6 μM for non-proteoid and juvenile proteoid roots under P-deficient conditions, suggesting the induction
of a high-affinity Pi-uptake system. Obviously, P-deficiency-induced adaptations of white lupin, involved in P acquisition
and mobilization of sparingly available P sources, are predominantly confined to proteoid roots, and moreover to distinct
stages during proteoid root development.
Received: 10 September 1998 / Accepted: 22 December 1998 相似文献
20.
A novel P-deficient mutant of Arabidopsis thaliana, pho3, was isolated by screening for root acid phosphatase (APase) activity in plants grown under low-P conditions. pho3 had 30% less APase activity in roots than the wild type and, in contrast to wild-type plants, root APase activity did not
increase in response to growth in low P. However, shoot APase activity was higher in pho3 than in the wild-type plants. In addition, the pho3 mutant had a P-deficient phenotype, even when grown in P-sufficient conditions. The total P content of 11-d-old pho3 plants, grown in agar media with a plentiful supply of P, was about 25% lower than the wild-type level in the shoot, and
about 65% lower in the roots. In the rosette leaves of mature soil-grown pho3 plants the total P content was again reduced, to about 50% of wild-type levels. pho3 exhibited a number of characteristics normally associated with low-P stress, including severely reduced growth, increased
anthocyanin content (at least 100-fold greater than the wild type in soil-grown plants) and starch accumulation. The results
suggest that the mutant is unable to respond to low internal P levels, and may lack a transporter or a signalling component
involved in regulating P nutrition.
Received: 21 March 2000 / Accepted: 15 August 2000 相似文献