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61.
P. lanceolata andP. major were grown in culture solutions with nitrate or ammonium as the nitrogen source. Dry matter accumulation in the shoot was
faster with nitrate than with ammonium, whilst that of the roots was not affected by the nitrogen source. As a consequence,
the shoot-to-root ratio was lower with ammonium than with nitrate. InP. lanceolata, dry matter percentage of shoot and root tissue was lower with nitrate nutrition, suggesting better elongation growth than
with ammonium. However, in shoot tissue ofP. major the opposite was found. The rate of root respiration declined with time, and this was almost completely due to a declining
activity of the alternative path, which amounted to about 30–60% of total root respiration. Respiration via the cytochrome
path was for a part of time slightly increased by ammonium, whereas the activity of the alternative path was strongly enhanced.
The concentration of ethanol-soluble carbohydrates (SC) in the roots of both species was higher when nitrate was used, but
no difference in the concentration of starch was found. When the plants were transferred from one nitrogen source to the other,
many parameters, including the concentration of nitrate and chloride, and the shoot to root ratio, adjusted to the new situation
in both species.
Grassland Species Research Group, Publication no. 116. 相似文献
62.
Growth of 2-month-old nonnodulatedHippophaë rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N2 fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH 4 + , a mixture of NH 4 + and NO 3 ? producing the highest yields. Growth was severely reduced when solely dependent on N2 fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio <5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N2-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO 3 ? dependent plants was almost entirely located in the roots. However, when grown with a combination of NO 3 ? and NH 4 + , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH 4 + , NO 3 ? contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO 3 ? +NH 4 + plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH 4 + plants than in the NO 3 ? plants. Measured extrusions of H+ or OH? (HCO 3 ? ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N2 fixation amounted to 0.45–0.55 meq H+. (mmol Norg)?1. Without acidity control and in the presence of NH 4 + , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N2-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites. 相似文献
63.
Oryzalin,a dinitroaniline herbicide,binds to plant tubulin and inhibits microtubule polymerization in vitro 总被引:11,自引:0,他引:11
The effects of oryzalin, a dinitroaniline herbicide, on chromosome behavior and on cellular microtubules (MTs) were examined by light microscopy and immunogold staining, respectively, in endosperm cells from Haemanthus katherinae Bak. Brief treatments with 1.0·10-8 M oryzalin reduced markedly the migration rate of anaphase chromosomes and 1.0·10-7 M oryzalin stopped migration abruptly. Oryzalin (1.0·10-7 M) depolymerized MTs and prevented the polymerization of new MTs at all stages of the mitotic cycle. The chromosome condensation cycle was unaffected by oryzalin. Endothelial cells from the heart of Xenopus leavis showed no chromosomal or microtubular rearrangements after oryzalin treatment. The inhibition by oryzalin of the polymerization of tubulin isolated from cultured cells of Rosa sp. cv. Paul's scarlet was examined in vitro by turbidimetry, electron microscopy and polymer sedimentation analysis. Oryzalin inhibited the rapid phase of taxol-induced polymerization of rose MTs at 24°C with an apparent inhibition constant (K
i
) of 2.59·106 M. Shorter and fewer MTs were formed with increasing oryzalin concentrations, and maximum inhibition of taxol-induced polymerization occurred at approx. 1:1 molar ratios of oryzalin and tubulin. Oryzalin partially depolymerized taxol-stabilized rose MTs. Ligand-binding experiments with [14C]oryzalin demonstrated the formation of a tubulin-oryzalin complex that was time- and pH-dependent. The tubulin-oryzalin interaction (24°C, pH 7.1) had an apparent affinity constant (K
app) of 1.19·105 M-1. Oryzalin did not inhibit taxol-induced polymerization of bovinebrain MTs and no appreciable binding of oryzalin to brain tubulin or other proteins was detected. The results demonstrate pharmacological differences between plant and animal tubulins and indicate that the most sensitive mode of action of the dinitroaniline herbicides is the direct poisoning of MT dynamics in cells of higher plants.Abbreviations MT
microtubule
- SIB
sucrose isolation buffer
- TO
tubulin-oryzalin complex 相似文献
64.
The crystal structure of the beta-lactamase of Streptomyces albus G at 0.3 nm resolution. 总被引:10,自引:3,他引:7
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O Dideberg P Charlier J P Wéry P Dehottay J Dusart T Erpicum J M Frère J M Ghuysen 《The Biochemical journal》1987,245(3):911-913
The crystal structure of the beta-lactamase of Streptomyces albus G has been solved at 0.3 nm resolution by X-ray-diffraction methods. The enzyme is a typical two-domain protein. One domain consists of five alpha-helices, and the other is five-stranded beta-sheet with alpha-helices on both sides of the sheet. The active-site serine residue (Ser-48) is within a cleft located between the two domains. 相似文献
65.
Early increases in the frequency of DNA initiations and of phospholipid synthesis discontinuities after nutritional shift-up in Escherichia coli 总被引:1,自引:0,他引:1
Cultures of Escherichia coli (strains ML30 and K12 AB1157), synchronized by repeated phosphate starvation, were submitted to nutritional shifts-up at various cell ages. The progression of the replication forks was assessed by DNA-DNA hybridization of pulse-labelled chromosomal DNA with plasmid DNA probes containing specific chromosomal sequences. The rate of phospholipid synthesis and its cyclic discontinuities were measured by continuous and pulse labelling with palmitate. The DNA-DNA hybridization experiments showed that a shift-up induces a burst of initiation from the oriC region. These hybridization results, taken together with older data from the literature, suggest that most DNA initiations belonging to this burst are not followed by complete replication. Following a shift-up, the rate of phospholipid synthesis is maintained for 13-20 min, depending on cell age at shift-up, then doubles. The new steady-state rate of phospholipid synthesis is reached through a series of three doublings, while the cell mass doubles approximately twice. This discrepancy brings the rate of phospholipid synthesis per mass unit to its steady-state postshift value. 相似文献
66.
When applied to ischemic hearts digitalis exhibits depressed inotropic effect and increased toxicity. The molecular basis of these effects was investigated at the level of the digitalis receptors characterized by Na,K-ATPase assays and [3H]ouabain-binding measurements. In sarcolemma obtained from dog hearts rendered ischemic for 15, 30, and 60 min (left anterior descending), two populations (high and low affinity) of digitalis receptors were detected. The apparent affinity (KD, 300 nM) and the binding capacity of the low-affinity sites (responsible for toxicity) remained constant and similar to those found in normal hearts. The KD value of the high-affinity sites, "responsible for inotropy," remained unchanged (2 nM), but the site number sharply decreased (up to 90%). These inotropic sites that account for 66% of the total binding in normals are gradually inactivated, as the duration of ischemia increases. This inactivation would occur in situ since it was detectable in homogenates and was not depressed by the isolation procedure per se. The loss of function of the inotropic sites and the increased contribution of the low-affinity toxic sites represent the setting of a new distribution of the digitalis receptors in the ischemic heart before reperfusion is instituted. This constitutes the molecular basis of the deleterious pharmacological effects observed with digitalis. 相似文献
67.
Interaction of epidermal growth factor with micelles monitored by photochemically induced dynamic nuclear polarization-1H NMR spectroscopy 总被引:1,自引:0,他引:1
K H Mayo A De Marco E Menegatti R Kaptein 《The Journal of biological chemistry》1987,262(31):14899-14904
Photochemically induced dynamic nuclear polarization (CIDNP)-1H-NMR spectroscopy has been used to study the interaction of the protein hormone epidermal growth factor (EGF) with micelles of sodium dodecyl sulfate (SDS) and dodecylphosphorylcholine (DPC). Conventional 1H-NMR spectra show that most protein resonances remain unperturbed when micelles are added to solution, which argues that the overall protein conformation is maintained in the presence of SDS or DPC at the concentrations used. Photo-CIDNP enhancements of resonances assigned to aromatic side chains of residues at the COOH terminus and beta-sheet regions of murine EGF (i.e. Trp-49, Trp-50, and Tyr-37) are considerably reduced in the presence of micelles, while resonances of aromatic side chains of residues found elsewhere on the protein surface are mostly unaffected. This suggests that the primary interaction between murine EGF and the micelle occurs at the micelle-bulk solvent interface. The overall negatively charged surface of SDS micelles tends to induce a stronger interaction with the protein compared to the zwitterionic DPC micelles, probably due to electrostatic interactions. Cleavage of the COOH-terminal pentapeptide containing both tryptophan residues enhances the already present, but weak, interaction with Tyr-10 and attenuates it with Tyr-37. A similar interaction pattern is found with rat EGF suggesting that at least concerning these two species of EGF the interaction is somewhat specific and conserved. A simple mass-action model for protein-micelle interaction is also presented. 相似文献
68.
Link protein interactions with hyaluronate and proteoglycans. Characterization of two distinct domains in bovine cartilage link proteins 总被引:4,自引:0,他引:4
J P Périn F Bonnet C Thurieau P Jollès 《The Journal of biological chemistry》1987,262(27):13269-13272
Hyaluronic acid-binding region and trypsin-link protein were prepared from bovine nasal cartilage proteoglycan complex after trypsin digestion. Binary complexes were reformed between trypsin-link protein and hyaluronic acid-binding region or hyaluronate. Upon trypsin treatment of these complexes, two fragments deriving from trypsin-link protein were characterized. One of them, of 20 kDa, corresponds in fact to a 140-amino acid long fragment and bears the glycosylated site of trypsin-link protein; it appears to be involved in proteoglycan/link protein interaction. The other, of 22 kDa, corresponds to the 200 C-terminal amino acids of trypsin-link protein; it appears to be involved in the binding of link protein with hyaluronic acid. A structural model of bovine trypsin-like protein depicting two distinct domains involved in hyaluronate and proteoglycan subunit interactions is proposed. 相似文献
69.
Evidence for negative regulation of T cell growth by low affinity interleukin 2 receptors 总被引:2,自引:0,他引:2
A Kumar J L Moreau D Baran J Thèze 《Journal of immunology (Baltimore, Md. : 1950)》1987,138(5):1485-1493
Two experimental situations have been studied, and the results provide evidence for a negative regulatory role for the low affinity interleukin 2 receptor (LA-IL 2R). The IL 2-dependent T helper cell line L-14, deprived of IL 2, becomes quiescent and expresses comparable numbers of high affinity IL 2R (HA-IL 2R) and LA-IL 2R. After activation by recombinant IL 2, this cell line preferentially expresses LA-IL 2R. The IL 2 responsiveness of the L-14 cell line was found to vary according to the ratio of LA-IL 2R to HA-IL 2R: the relative predominance of the LA-IL 2R coincides with a hyporeactivity of cells to IL 2. In contrast, a predominance of HA-IL 2R is accompanied by an increase in cellular IL 2 reactivity. Treatment of three IL 2-dependent T cell lines (L-14, HT-2, and C30.1) with limited amounts of recombinant IL 2 and moderate concentrations of anti-IL 2R monoclonal antibodies stimulates T cell growth. This treatment was shown to selectively diminish the expression of membrane LA-IL 2R. The stimulation was attributed to the decrease of expression of LA-IL 2R. 相似文献
70.
Ann M. G. L. De Mazière Dietrich W. Scheuermann Philip A. P. M. Aertgeerts 《The Journal of membrane biology》1987,97(2):107-115
Summary Particles and pits of freeze-fractured gap junctions are considered as complementary structures despite the frequent observations of more regular and closer spacings of pits, ascribed to plastic deformation of particle arrays. Recently, however, the noncomplementarity of pits and particles in Purkinje fibers has been reported. To ascertain the relationship between both structures, gap junctions from fixed, cryoprotected liver and myocardium were investigated using spacing and density measurements and complementary replicas.In hepatocyte gap junctions, the center-to-center distances (mean±sd) among pits, 9.57±1.49 nm, and particles, 9.70±1.77 nm, are not significantly different. Density determinations yielded a slightly higher value for the pits, (11,510±830)/m2, than for the particles, (11,230±950)/m2. In the myocardium, the spacing of the regularly arrayed pits, 9.55±1.33 nm barely exceeds the value of 9.44±1.62 nm for the particles, which show some clustering. However, the packing density for the pits, (10,090±740)/m2, appears a little higher than that of the particles (9,890±920)/m2. As density and spacing measurements provided no decisive answers, the positions of individual pits and particles of complementary junctional faces were recorded on transparent sheets and compared. In this fashion, a one-to-one correspondence between particles and pits could be established, while small discrepancies may be attributed to plastic deformation. Moreover, the collinearity of pits and particles may be suggested by the observation of a platinum grain in the center of many pits. 相似文献