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81.
The role of acid phosphatases in plant phosphorus metabolism 总被引:18,自引:0,他引:18
Hydrolysis of phosphate esters is a critical process in the energy metabolism and metabolic regulation of plant cells. This review summarizes the characteristics and putative roles of plant acid phosphatase (APase). Although immunologically closely related, plant APases display remarkable heterogeneity with regards to their kinetic and molecular properties, and subcellular location. The secreted APases of roots and cell cultures are relatively non-specific enzymes that appear to be important in the hydrolysis and mobilization of Pi from extracellular phosphomonoesters for plant nutrition. Intracellular APases are undoubtedly involved in the routine utilization of Pi reserves or other Pi -containing compounds. A special class of intracellular APase exists that demonstrate a clear-cut (but generally nonabsolute) substrate selectivity. These APases are hypothesized to have distinct metabolic functions and include: phytase, phosphoglycolate phosphatase, 3-phosphoglycerate phosphatase, phosphoenolpyruvate phosphatase, and phosphotyrosyl-protein phosphatase. APase expression is regulated by a variety of developmental and environmental factors. Pi starvation induces de novo synthesis of extra- and intracellular APases in cell cultures as well as in whole plants. Recommendations are made to achieve uniformity in the analyses of the different APase isoforms normally encountered within and between different plant tissues. 相似文献
82.
J. Sklenar G. G. Fox B. C. Loughman A. D. B. Pannifer R. G. Ratcliffe 《Plant and Soil》1994,167(1):57-62
Although the sensitivity of the plasma membrane H+-ATPase to vanadate is well known, the metabolic response of plant cells to vanadate is less well characterised in vivo and its use as an inhibitor in whole plant experiments has had mixed success. Experiments with maize (Zea mays, L.) roots and with purified plasma membrane fractions from the same tissues showed that exposure to vanadate caused: (i) a reduction in the capacity for phosphate uptake; (ii) a reduction in the extractable ATPase activity from the tissue; and (iii) a significant increase in the ATP level. The measurements on the extractable ATPase activity and the ATP level showed that the effect of vanadate developed slowly, apparently reflecting the slow accumulation of intracellular vanadate. The marked effect of vanadate on the ATP level-exposure to 500 M vanadate for 5 h doubled the ATP content of the roots tips-indicates that there is no stringent control over the ATP level in the roots and that the plasma membrane H+-ATPase activity is likely to have a significant role in determining the ATP level under normal conditions. 相似文献
83.
Effect of shock-loading of heavy metals on total organic carbon and phosphate removal in an anaerobic-aerobic activated sludge process 总被引:1,自引:0,他引:1
The effect of shock-loading of zinc, copper and cadmium ions on the removal of total organic carbon (TOC) and phosphate in an anaerobic-aerobic activated sludge process was investigated. TOC removal was not sensitive to shock-loading of Zn2+ and Cd2+ ions, and complete removal was achieved even at 20 mg Zn2+/l and 20 mg Cd2+/l. However, with over 1 mg Cu2+/1 TOC removal efficiency decreased. PO
inf4
sup3-
removal, in contrast, was extremely sensitive to these metal ions, with the threshold being 1 mg Zn2+/l and 1 mg Cd2+/l. Higher concentrations adversely affected PO
inf4
sup3-
removal. Copper again proved detrimental; no PO
inf4
sup3-
removal was achieved even at 1 mg Cu/l. These results highlight the sensitivity of the removal efficiencies of TOC and PO
inf4
sup3-
to shock loadings of these heavy metals.Y.P. Ting is with the Department of Chemical Engineering, National University of Singapore, Kent Ridge, 0511, Singapore; H. Imai and S. Kinoshita are with the Department of Chemical Process Engineering, Hokkaido University, Sapporo 060, Japan. 相似文献
84.
Similarity between pyridoxal/pyridoxamine phosphate-dependent enzymes involved in dideoxy and deoxyaminosugar biosynthesis and other pyridoxal phosphate enzymes. 总被引:1,自引:0,他引:1
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A multiple sequence alignment among aspartate aminotransferase, dialkylglycine decarboxylase, and serine hydroxymethyltransferase (DAS) was used for profile databank search. The DAS profile could detect similarities to other pyridoxal or pyridoxamine phosphate-dependent enzymes, like several gene products involved in dideoxysugar and deoxyaminosugar synthesis. The alignment among DAS and such gene products shows the conservation of aspartate 222 and lysine 258, which, in aspartate aminotransferase, interacts with the N1 of the coenzyme pyridine ring and forms the internal Schiff base, respectively. The lysine is replaced by histidine in the pyridoxamine phosphate-dependent gene products. The alignment indicates also that the region encompassing the coenzyme binding site is the most conserved. 相似文献
85.
Calvin cycle genes in Nitrobacter vulgaris T3 总被引:1,自引:0,他引:1
Maren Strecker Eva Sickinger Robert S. English Jessup M. Shively 《FEMS microbiology letters》1994,120(1-2):45-50
Abstract The genes encoding the Calvin cycle enzymes of Nitrobacter vulgaris T3 are found as two separate clusters on the chromosome. One cluster contains the genes for the large and small subunits of ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCO), glyceraldehyde-3-phosphate dehydrogenase, and one encoding a regulatory protein of the LysR family. The other cluster contains the genes for fructose-1,6-/sedoheptulose-1,7-bisphosphatase, phosphoribulokinase, and fructose-1,6-/sedoheptulose-1,7-biphosphate aldolase. With the exception of the LysR-like gene, the genes in each cluster are apparently transcribed in the same direction. The deduced amino acid sequence of both the large and small subunits of RuBisCO are most similar (84–86%) to those of Thiobacillus ferrooxidans and Chromatium vinosum . The deduced sequences of phosphoribulokinase and fructose/sedoheptulose bisphosphatase are 67–73 aand 44–46% similar to those reported for other autotrophic bacteria, respectively. 相似文献
86.
E. Iglesias Jimenez V. Perez Garcia M. Espino J. M. Hernandez Moreno 《Plant and Soil》1993,148(1):115-127
In sesquioxide-rich soils of tropical and subtropical areas and volcanic-ash soils with high levels of active Al(Fe), large amounts of phosphate fertilizers are needed to overcome their high P-fixation capacity (quenching strategy). A greenhouse pot experiment has been used to evaluate the effectiveness of city refuse compost (CRC) as a P-source for these variable-charge soils, compared to inorganic P. Mature CRC and K2HPO4 were applied at rates equivalent to 125, 250, 375, 500 and 625 kg P ha–1 to a ferrallitic soils from Tenerife Island (Andeptic Paleudult) with a high content in active Al+Fe (4.82%) and a high P-fixation capacity (87%). Perennial ryegrass (Lolium perenne L.) was grown in pots and plants were harvested at regular intervals after seedling emergence. CRC increases plant P concentration and soil labile-P proportional to the applied rate. The best results were obtained from a compost application of 30 t ha–1 equivalent-rate, after a residence time of at least three months. An important residual effect in the supply capacity of P in relation to the phosphate fertilizer was also observed. The relative agronomic effectiveness (RAE) in comparison to K2HPO4 was 66% after 6 months, considering P uptake + soil labile-P. The soil P-fixation capacity was significantly reduced from a compost application of 40 t ha–1 equivalent-rate. Competition in adsorption between organic ligands and phosphate, in combination with net mineralization of organic P in compost, might account for the high RAE value obtained. The main conclusion is that the city refuse compost could be a suitable P-amendment for resquioxic soils due to its high RAE, and the residual effect on P-supply. ei]H. Lambers 相似文献
87.
The long-term effects of biological agents alone and in combination with monoammonium phosphate on tree growth and fruit production
of apple trees planted on apple replant soil was studied for five years. Application of monoammonium phosphate (MAP) in the
year of planting increased shoot growth, cross-sectional trunk area and fruit yield of McIntosh on M.26 rootstock for the
first two years. The application of bacterial agents alone were not effective in increasing young tree growth except BACT-1
in 1987. None of the bacterial agents increased fruit yield when applied alone. The addition of certain bacterial agents to
MAP application increased young tree growth in various years. The combination of bacterial agent B-10 and MAP reduced young
tree growth and yield compared with the MAP treatment alone. These results suggest that the application of MAP alone may be
sufficient to alleviate the replant problem and the addition of BACT-1, EBW-4 or B8 bacterial agents to this treatment may
be beneficial to increase tree growth in some years.
Contribution number 822.
Contribution number 822. 相似文献
88.
In vivo photosynthetic electron transport does not limit photosynthetic capacity in phosphate-deficient sunflower and maize leaves 总被引:8,自引:0,他引:8
The effects of extreme phosphate (Pi) deficiency during growth on the contents of adenylates and pyridine nucleotides and the in vivo photochemical activity of photosystem II (PSII) were determined in leaves of Helianthus annuus and Zea mays grown under controlled environmental conditions. Phosphate deficiency decreased the amounts of ATP and ADP per unit leaf area and the adenylate energy charge of leaves. The amounts of oxidized pyridine nucleotides per unit leaf area decreased with Pi deficiency, but not those of reduced pyridine nucleotides. This resulted in an increase in the ratio of reduced to oxidized pyridine nucleotides in Pi-deficient leaves. Analysis of chlorophyll a fluorescence at room temperature showed that Pi deficiency decreased the efficiency of excitation capture by open PSII reaction centres (φe), the in vivo quantum yield of PSII photochemistry (φPSII) and the photochemical quenching co-efficient (qP), and increased the non-photochemical quenching co-efficient (qN) indicating possible photoinhibitory damage to PSII. Supplying Pi to Pi-deficient sunflower leaves reversed the long-term effects of Pi-deficiency on PSII photochemistry. Feeding Pi-sufficient sunflower leaves with mannose or FCCP rapidly produced effects on chlorophyll a fluorescence similar to long-term Pi-deficiency. Our results suggest a direct role of Pi and photophosphorylation on PSII photochemistry in both long-and short-term responses of photosynthetic machinery to Pi deficiency. The relationship between φPSII and the apparent quantum yield of CO2 assimilation determined at varying light intensity and 21 kPa O2 and 35 Pa CO2 partial pressures in the ambient air was linear in Pi-sufficient and Pi-deficient leaves of sunflower and maize. Calculations show that there was relatively more PSII activity per mole of CO2 assimilated by the Pi-deficient leaves. This indicates that in these leaves a greater proportion of photosynthetic electrons transported across PSII was used for processes other than CO2 reduction. Therefore, we conclude that in vivo photosynthetic electron transport through PSII did not limit photosynthesis in Pi-deficient leaves of sunflower and maize and that the decreased CO2 assimilation was a consequence of a smaller ATP content and lower energy charge which restricted production of ribulose, 1-5, bisphosphate, the acceptor for CO2. 相似文献
89.
The requirement of inorganic phosphate (Pi) for oxidative phosphorylation in eukaryotic cells is fulfilled through specific Pi transport systems. The mitochondrial proton/phosphate symporter (Pic) is a membrane-embedded protein which translocates Pi from the cytosol into the mitochondrial matrix. Pic is responsible for the very rapid transport of most of the Pi used in ATP synthesis. During the past five years there have been advances on several fronts. Genomic and cDNA clones for yeast, bovine, rat, and human Pic have been isolated and sequenced. Functional expression of yeast Pic in yeast strains deficient in Pi transport and expression inEscherichia coli of a chimera protein involving Pic and ATP synthase subunit have been accomplished. Pic, in contrast to other members of the family of transporters involved in energy metabolism, was demonstrated to have a presequence, which optimizes the import of the precursor protein into mitochondria. Six transmembrane segments appear to be a structural feature shared between Pic and other mitochondrial anion carriers, and recent-site directed mutagenesis studies implicate structure-functional relationships to bacteriorhodopsin. These recent advances on Pic will be assessed in light of a more global interpretation of transport mechanism across the inner mitochondrial membrane. 相似文献
90.
This article concerns seasonal variations in the phosphate concentrations in two coastal lagoons near Montpellier (Mediterranean
coast, France). The o-P concentration in the overlying water is highest during summer. The role of the sediment, particularly
that of the different P fractions in the sediment, is discussed. Significant variations, especially in the FeOOH ≈ P fraction,
occur. For both Tot-Psed and the Fe00H≈P fraction a gradient from surface to bottom is observed, as well as a distinct decrease in the FeOOH≈P fraction
in the surface sediments during summer and autumn. Variations in the FeOOH≈P fraction appear to be compensated by variations
in the CaC03≈P fraction. These variations appear to be determined by the ferric hydroxide concentration. This compound represents only
a small part (maximally 15%) of the total iron in the sediments and is related to the dissolved oxygen content of the immediately
overlying water. Besides the fractions o-P, Fe(OOH)≈P, a large part of the CaC03≈P fraction is potentially bioavailable. A large proportion of the Tot-Psed is therefore bioavailable.[/p] 相似文献