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911.
Gert Arnold 《Plant and Soil》1992,142(1):41-51
Three-year-old Scots pine (Pinus sylvestris) trees were grown on a sandy forest soil in pots, with the objective to determine their NH4/NO3 uptake ratio and proton efflux. N was supplied in three NH4-N/NO3-N ratios, 3:1, 1:1 and 1:3, either as 15NH4+14NO3 or as 14NH4+15NO3. Total N and 15N acquisition of different plant parts were measured. Averaged over the whole tree, the NH4/NO3 uptake ratios throughout the growing season were found to be 4.2, 2.5, and 1.5 for the three application ratios, respectively.
The excess cation-over-anion uptake value (Ca-Aa) appeared to be linearly related to the natural logarithm of the NH4/NO3 uptake ratio. Further, this uptake ratio was related to the NH4/NO3 ratio of the soil solution. From these relationship it was estimated that Scots pine exhibits an acidifying uptake pattern
as long as the contribution of nitrate to the N nutrition is lower than 70%. Under field circumstances root uptake may cause
soil acidification in the topsoil, containing the largest part of the root system, and soil alkalization in deeper soil layers. 相似文献
912.
Genetics of leucine aminopeptidase in apple 总被引:1,自引:0,他引:1
A. G. Manganaris F. H. Alston 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,83(3):345-352
Summary Six zones of LAP activity were detected in apples, some of them tissue specific. Genetic studies in four of them revealed the presence of four genes LAP-1, LAP-2, LAP-3 and LAP-4 with 4, 5, 4 and 4 alleles respectively including two null alleles. There were no big differences in allelic frequency within cultivars, selections, rootstocks and Malus species. Close linkage was found between LAP-2 and resistance to mildew derived from White Angel. 相似文献
913.
A. G. Manganaris F. H. Alston 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1992,83(4):467-475
Summary Three main zones of esterase activity (EST-I, EST-III, EST-IV) identified in leaf extracts of cultivated apple and Malus species were determined by the genes EST-1, EST-3 and EST-4, respectively. In addition to earlier reported alleles of EST-1 (a, b) three further bands c, d and f were identified in the EST-I zone of which c was found to be determined by an allele, c. Two alleles, a, b, and a null allele were found for both the genes EST-3 and EST-4. Differences in allelic frequency were observed between cultivars, rootstocks and Malus species. Allele EST-1a was rare amongst the rootstocks. The examination of Malus species and derivatives showed a geographical relationship. Allele EST-1c was confined to species of Asian origin, and EST-1d was confined to American species. 相似文献
914.
Carbon: terrestrial C4 plants 总被引:1,自引:1,他引:0
The carbon isotope composition of terrestrial C4 plants depends on the primary carboxylation of phosphoenolpyruvate (PEP) and on the diffusion of CO2 to the carboxylation sites, but is also influenced by the final carboxylation of ribulose-1,5-bisphosphate (RuBP). Several models have been used for reproducing this complex situation. In the present review, a particular model is applied as a means to interpret the effects of environmental and genetically determined factors on carbon isotope discrimination during C4 photosynthesis. As a new feature, the model considers four types of limitation of the overall CO2 assimilation rate. Both carboxylation reactions are assumed to be limited by either maximum enzyme activity or maximum substrate regeneration rate. The model is applied to experimental data on the effects of CO2, irradiance and water stress on short-term discrimination by leaves of several C4 species measured simultaneously with CO2 gas exchange characteristics. In particular, different patterns of the influence of low irradiances on carbon isotope discrimination are interpreted as due to variations in that irradiance at which a transition from limitation by PEP regeneration rate and RuBP carboxylase activity to limitation by the regeneration rates of both substrates occurs. After discussing literature data on the effects of environmental conditions on carbon isotope discrimination by C4 plants seasonal and developmental changes in carbon isotope composition, studies on the systematic and geographic distribution of C4 plants, evolutionary and genetical aspects, and some ecological implications are reviewed. 相似文献
915.
Carbon isotope discrimination in C3 -C4 intermediates 总被引:1,自引:1,他引:0
Carbon isotope discrimination in C3–C4 intermediates is determined by fractionations during diffusion and the biochemical fractionations occurring during CO2 fixation. These biochemical fractionations in turn depend on the fractionation by Rubisco in the mesophyll, the amount of CO2 fixation. These biochemical fractionations in turn depend on the fractionation by Rubisco in the mesophyll, the amount of CO2 fixation occurring in the bundle sheath, the extent of bundle-sheath leakiness and the contribution which C4-cycle activity makes to the CO2 pool there. In most instances, carbon isotope discrimination in C3–C4 intermediates is C3-like because only a small fraction of the total carbon fixed is fixed in the bundle sheath. In particular, this must be the case for Flaveria intermediates which initially fix substantial amounts of CO2 into C4-acids. In C3–C4 intermediates that refix photorespiratory CO2 alone, it is possible for carbon isotope discrimination to be greater than in C3-species, particularly at low CO2 pressures or at high leaf temperatures. Short-term measurements of carbon isotope discrimination and gas exchange of leaves can be used to study the photosynthetic pathways of C3-C4 intermediates and their hybrids as has recently been done for C3 and C4 species. 相似文献
916.
Krishan K. Arora David M. Parry Peter L. Pedersen 《Journal of bioenergetics and biomembranes》1992,24(1):47-53
Hexokinase plays an important role in normal glucose-utilizing tissues like brain and kidney, and an even more important role in highly malignant cancer cells where it is markedly overexpressed. In both cell types, normal and transformed, a significant portion of the total hexokinase activity is bound to particulate material that sediments upon differential centrifugation with the crude mitochondrial fraction. In the case of brain, particulate binding may constitute most of the total hexokinase activity of the cell, and in highly malignant tumor cells as much as 80 percent of the total. When a variety of techniques are rigorously applied to better define the particulate location of hexokinase within the crude mitochondrial fraction, a striking difference is observed between the distribution of hexokinase in normal and transformed cells. Significantly, particulate hexokinase found in rat brain, kidney, or liver consistently distributes with nonmitochondrial membrane markers whereas the particulate hexokinase of highly glycolytic hepatoma cells distributes with outer mitochondrial membrane markers. These studies indicate that within normal tissues hexokinase binds preferentially to non-mitochondrial receptor sites but upon transformation of such cells to yield poorly differentiated, highly malignant tumors, the overexpressed enzyme binds preferentially to outer mitochondrial membrane receptors. These studies, taken together with the well-known observation that, once solubilized, the particulate hexokinase from a normal tissue can bind to isolated mitochondria, are consistent with the presence in normal tissues of at least two different types of particulate receptors for hexokinase with different subcellular locations. A model which explains this unique transformation-dependent shift in the intracellular location of hexokinase is proposed. 相似文献
917.
The role of transferrin in iron metabolism is evaluated, both with regard to iron uptake by transferrin and to iron uptake
from transferrin by different cells. The heterogeneity of serum transferrin is described and the implications of the heterogeneity
are discussed. The composition of ferritin is given and the value of serum ferritins are discussed. 相似文献
918.
J. S. Starreveld A. M. Abdoel J. P. v. Dijk M. J. Kroos H. G. v. Eijk 《Biological trace element research》1992,35(1):55-63
During pregnancy, the mother is faced with an increased food demand. A good example of this increased demand is iron (Fe).
Fe is needed in all growing cells. During pregnancy, the Fe transport to the fetus increases enormously. This amount can easily
induce an Fe deficiency in the mother. Fe suppletion is very important for her, but not for the Fe status of the fetus, which
is protected against Fe toxicity as well as deficiency. The placenta seems to be autonomous in Fe uptake. Likely there is
a regulation mechanism. The human placenta is hemomonochorial. The cell layer of the fetus in contact with the maternal blood
is formed by syncytiotrophoblasts. Fe is transported to the placenta by transferrin. Transferrin binds to a transferrin receptor
on the trophoblast membrane and is internalized via an endocytic pathway. During this cycle, Fe is released from transferrin
and the transferrin-transferrin receptor complex is recycled to the membrane. Isolated trophoblast cells from term placentas
form a syncytium in vitro, and transferrin receptors are expressed. Expression depends on the number of cells in culture,
culture time, the amount of Fe available, and the Fe compound. By regulation of the number of transferrin receptors, trophoblasts
are able to control their Fe uptake. 相似文献
919.
We have determined the nucleotide sequence of a cDNA encoding AlaAT-2, which is believed to function in the C4-pathway of Panicum miliaceum. An open reading frame (1446 bp) encodes a protein of 482 amino acid residues. The deduced amino acid sequence of AlaAT-2 shows 44.2 and 44.8% homology with the amino acid sequences of AlaATs from rat and human livers, respectively. Northern blot analysis showed that the gene encoding AlaAT-2 in mesophyll and bundle sheath cells was the same and transcribed similarly in the cells. The level of translatable mRNA for AlaAT-2 increased dramatically during greening. 相似文献
920.
An antiserum against gibberellin A4 (GA4) raised in rabbits and its partially purified antibodies were used to develop radioimmunoassay (RIA) and indirect enzyme-linked immunosorbent assays (ELISAs) for GA4. Of three immunoassays tested, an ELISA based on the NAD-dependent redox cycle (enzyme-amplified ELISA) had highest sensitivity. Levels of methylated GA4 detected by this most sensitive method ranged from 0.1 fmol/assay (3.5 fg/assay) to 0.1 pmol/assay (3.5 pg/assay) suggesting applicability of this method to the detection of gibberellins in purified plant extracts. 相似文献