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81.
Preferential utilization of organic and inorganic sources of phosphorus by wheat plant 总被引:3,自引:0,他引:3
On soils of low P supply organic P (Po) makes up a similar or even larger part in soil solution than inorganic P (Pi). The
ability of wheat (Triticum aestivum L., cv. Star) plants to hydrolyze and absorb this Po in comparison to similar concentrations of Pi was studied. Four concentration
levels of Pi and Po were obtained by extracting two soils with deionized water in a ratio of 1:1 and concentrating the resulting
filtrate by freeze drying to different degrees. The concentration of Pi varied between 5 and 36 μM and Po between 3 and 22 μM. Wheat seedlings were grown in these solutions for 12 and 24 h and acid and alkaline phosphatase activity determined. The
reduction of Po concentration in solution expressed on a root length basis gave the rate of Po hydrolysis and the reduction
in concentration of Pi and Po gave the P inflow into the roots. No alkaline phosphatase activity was detected. The activity
of wheat root acid phosphatase increased with Po concentration in solution. Phosphorus uptake was 2 to 6 fold higher from
Pi than from Po at similar concentrations of both. The rate of uptake from Pi, the inflow, as well as the rate of hydrolysis
of Po increased linearly with concentration but at similar concentration the inflow was 2 to 4 times higher than the rate
of Po hydrolysis. Results suggest that plants can utilize Po after hydrolysis by phosphatase, but Pi is more important and
preferentially used by plants; Po may be essential for plant nutrition especially in high P-fixing soils. 相似文献
82.
Rationale for adjuvant fatty acid therapy to prevent radiotherapy failure and tumor recurrence during early laryngeal squamous cell carcinoma 总被引:1,自引:0,他引:1
Information from a preceding lipid study contributed to the pathobiological assessment of laryngeal squamous cell carcinoma (LSCC). Lipid-driven signaling pathways are responsible for laryngeal carcinogenesis and immunodeficiency. The construction of fatty acid (FA) profiles for LSCC allowed the identification of FA role players. The integration of lipid and clinicomolecular information encountered in the literature, in turn, allowed the identification of biological prognostic markers to distinguish between early (less aggressive) and advanced (more aggressive) LSCCs. High arachidonic acid (AA) and cyclooxygenase (COX-2) activities are criteria for less aggressive growth, whilst low AA and COX-2 activities occur during more aggressive growth. Excessive tobacco use and environmental smoke or human papillomavirus (HPV) infection and alcohol abuse can, respectively, elicit cumulative oxidative stress and an oxidative burst or interfere with signaling pathways during essential fatty acid (EFA) metabolism, all factors and events which may cause LSCC. Research revealed that enhanced COX-2 activity and Bcl-2 expression prevent apoptosis and, hence, LSCCs become resistant to radiotherapy. It was also observed that recurrent laryngeal cancers become more aggressive after radiotherapy failure. It is predicted that manipulation of AA activity and consequently a cascade of downstream factors that include COX-2 and Bcl-2 expression responsible for LSCC may have therapeutic potential to improve radiotherapy outcome during early LSCC. Adjuvant FA therapy to improve early LSCC management by counteracting radiotherapy failure and unwanted complications for further management is proposed. FA therapeutic strategies before and during radiotherapeutic courses need to be evaluated. 相似文献
83.
Clostridium beijerinckii Cells Expressing Neocallimastix patriciarum Glycoside Hydrolases Show Enhanced Lichenan Utilization and Solvent Production 总被引:1,自引:0,他引:1 下载免费PDF全文
Ana M. Lpez-Contreras Hauke Smidt John van der Oost Pieternel A. M. Claassen Hans Mooibroek Willem M. de Vos 《Applied microbiology》2001,67(11):5127-5133
Growth and the production of acetone, butanol, and ethanol by Clostridium beijerinckii NCIMB 8052 on several polysaccharides and sugars were analyzed. On crystalline cellulose, growth and solvent production were observed only when a mixture of fungal cellulases was added to the medium. On lichenan growth and solvent production occurred, but this polymer was only partially utilized. To increase utilization of these polymers and subsequent solvent production, the genes for two new glycoside hydrolases, celA and celD from the fungus Neocallimastix patriciarum, were cloned separately into C. beijerinckii. To do this, a secretion vector based on the pMTL500E shuttle vector and containing the promoter and signal sequence coding region of the Clostridium saccharobutylicum NCP262 eglA gene was constructed and fused either to the celA gene or the celD gene. Stable C. beijerinckii transformants were obtained with the resulting plasmids, pWUR3 (celA) and pWUR4 (celD). The recombinant strains showed clear halos on agar plates containing carboxymethyl cellulose upon staining with Congo red. In addition, their culture supernatants had significant endoglucanase activities (123 U/mg of protein for transformants harboring celA and 78 U/mg of protein for transformants harboring celD). Although C. beijerinckii harboring either celA or celD was not able to grow, separately or in mixed culture, on carboxymethyl cellulose or microcrystalline cellulose, both transformants showed a significant increase in solvent production during growth on lichenan and more extensive degradation of this polymer than that exhibited by the wild-type strain. 相似文献
84.
Influence of a natural and a synthetic inhibitor of factor XIIIa on fibrin clot rheology 总被引:2,自引:0,他引:2 下载免费PDF全文
We investigated the origins of greater clot rigidity associated with FXIIIa-dependent cross-linking. Fibrin clots were examined in which cross-linking was controlled through the use of two inhibitors: a highly specific active-center-directed synthetic inhibitor of FXIIIa, 1,3-dimethyl-4,5-diphenyl-2[2(oxopropyl)thio]imidazolium trifluoromethylsulfonate, and a patient-derived immunoglobulin directed mainly against the thrombin-activated catalytic A subunits of thrombin-activated FXIII. Cross-linked fibrin chains were identified and quantified by one- and two-dimensional gel electrophoresis and immunostaining with antibodies specific for the alpha- and gamma-chains of fibrin. Gamma-dimers, gamma-multimers, alpha(n)-polymers, and alpha(p)gamma(q)-hybrids were detected. The synthetic inhibitor was highly effective in preventing the production of all cross-linked species. In contrast, the autoimmune antibody of the patient caused primarily an inhibition of alpha-chain cross-linking. Clot rigidities (storage moduli, G') were measured with a cone and plate rheometer and correlated with the distributions of the various cross-linked species found in the clots. Our findings indicate that the FXIIIa-induced dimeric cross-linking of gamma-chains by itself is not sufficient to stiffen the fibrin networks. Instead, the augmentation of clot rigidity was more strongly correlated with the formation of gamma-multimers, alpha(n)-polymers, and alpha(p)gamma(q)-hybrid cross-links. A mechanism is proposed to explain how these cross-linked species may enhance clot rigidity. 相似文献
85.
Frequency-domain analyses were used to determine the effect of cold stress on the relationships between the discharge bursts of sympathetic nerve pairs, sympathetic and aortic depressor nerve pairs, and sympathetic and phrenic nerve pairs in chloralose-anesthetized, baroreceptor-innervated rats. Sympathetic nerve discharge (SND) was recorded from the renal, lumbar, splanchnic, and adrenal nerves during decreases in core body temperature from 38 to 30 degrees C. The following observations were made. 1) Hypothermia produced nonuniform changes in the level of activity in regionally selective sympathetic nerves. Specifically, cold stress increased lumbar and decreased renal SND but did not significantly change the level of activity in splanchnic and adrenal nerves. 2) The cardiac-related pattern of renal, lumbar, and splanchnic SND bursts was transformed to a low-frequency (0-2 Hz) pattern during cooling, despite the presence of pulse-synchronous activity in arterial baroreceptor afferents. 3) Peak coherence values relating the discharges between sympathetic nerve pairs decreased at the cardiac frequency but were unchanged at low frequencies (0-2 Hz), indicating that the sources of low-frequency SND bursts remain prominently coupled during progressive reductions in core body temperature. 4) Coherence of discharge bursts in phrenic and renal sympathetic nerve pairs in the 0- to 2-Hz frequency band increased during mild hypothermia (36 degrees C) but decreased during deep hypothermia (30 degrees C). We conclude that hypothermia profoundly alters the organization of neural circuits involved in regulation of sympathetic nerve outflow to selected regional circulations. 相似文献
86.
Reestablishing native perennial plants and reducing invasive species are pivotal for many ecological restoration projects. The interactions among plant species, arbuscular mycorrhizal fungi, and soil P availability may be critical determinants of the success of native and non‐native plants in restoration and species invasions. Here we assessed mycorrhizal responsiveness for three late‐successional and three early‐successional plant species native to Rocky Mountain National Park and for the non‐native Downy brome, cheatgrass (Bromus tectorum L.) using field soil and commercial inoculum. Factorial greenhouse experiments were conducted to compare biomass of plant species with and without field soil and commercial inoculum treatments along a phosphorus (P) gradient, which ranged from ambient field levels to 12% of field levels, using dilutions of native soils. The two field soil inoculum treatments resulted in significant biomass differences for all species studied. Late‐successional species responded positively to field inoculum, whereas early‐successional species responded negatively. The two commercial inocula had low colonization rates (14 of 166 inoculated plants). The commercial inocula substrates had significant treatment effects on five of seven species included in the study in the apparent absence of mycorrhizal symbiosis. Soil P levels influenced mycorrhizal responsiveness in only one species, Smooth blue aster (Aster laevis L.). Our results show that, at least for the species studied here, locally collected field inoculum is the best choice for reestablishment of late‐successional native plant species. 相似文献
87.
Kuzoff RK; Sweere JA; Soltis DE; Soltis PS; Zimmer EA 《Molecular biology and evolution》1998,15(3):251-263
18S ribosomal RNA genes are the most widely used nuclear sequences for
phylogeny reconstruction at higher taxonomic levels in plants. However, due
to a conservative rate of evolution, 18S rDNA alone sometimes provides too
few phylogenetically informative characters to resolve relationships
adequately. Previous studies using partial sequences have suggested the
potential of 26S or large-subunit (LSU) rDNA for phylogeny retrieval at
taxonomic levels comparable to those investigated with 18S rDNA. Here we
explore the patterns of molecular evolution of entire 26S rDNA sequences
and their impact on phylogeny retrieval. We present a protocol for PCR
amplification and sequencing of entire (approximately 3.4 kb) 26S rDNA
sequences as single amplicons, as well as primers that can be used for
amplification and sequencing. These primers proved useful in angiosperms
and Gnetales and likely have broader applicability. With these protocols
and primers, entire 26S rDNA sequences were generated for a diverse array
of 15 seed plants, including basal eudicots, monocots, and higher eudicots,
plus two representatives of Gnetales. Comparisons of sequence dissimilarity
indicate that expansion segments (or divergence domains) evolve 6.4 to 10.2
times as fast as conserved core regions of 26S rDNA sequences in plants.
Additional comparisons indicate that 26S rDNA evolves 1.6 to 2.2 times as
fast as and provides 3.3 times as many phylogenetically informative
characters as 18S rDNA; compared to the chloroplast gene rbcL, 26S rDNA
evolves at 0.44 to 1.0 times its rate and provides 2.0 times as many
phylogenetically informative characters. Expansion segment sequences
analyzed here evolve 1.2 to 3.0 times faster than rbcL, providing 1.5 times
the number of informative characters. Plant expansion segments have a
pattern of evolution distinct from that found in animals, exhibiting less
cryptic sequence simplicity, a lower frequency of insertion and deletion,
and greater phylogenetic potential.
相似文献
88.
89.
Synemin and vimentin are components of intermediate filaments in avian erythrocytes 总被引:32,自引:21,他引:11 下载免费PDF全文
Synemin, a high-molecular-weight protein associated with intermediate filaments in muscle, and vimentin, an intermediate-filament subunit found in many different cell types, have been identified by immunologic and electrophoretic criteria as components of intermediate filaments in mature avian erythrocytes. Desmin, the predominant subunit of intermediate filaments in muscle, has not been detected in these cells. Two dimensional immunoautoradiography of proteolytic fragments of synemin and vimentin demonstates that the erythrocyte proteins are highly homologous, if not identical, to their muscle counterparts. Double immunoflurorescence reaveals that erythrocyte synemin and vimentin co-localize in a cytoplasmic network of sinuous filaments that extends from the nucleus to the plasma membrane and resists aggregation by colcemid. Erythrocytes that are attached to glass cover slips can be sonicated to remove nuclei and nonadherent regions of the plasma membrane; this leaves elliptical patches of adherent membrane that retain mats of vimentin- and synemin-containing intermediate filaments, as seen by immunofluorescence and rotary shadowing. Similarly, mechanical enucleation of erythrocyte ghosts in suspension allows isolation of plasma membranes that retain a significant fraction of the synemin and vimentin, as assayed by electrophoresis, and intermediate filaments, as seen in thin sections. Both synemin and vimentin remain insoluble along with spectrin and actin, in solutions containing nonionic detergent and high salt. However, brief exposure of isolated membrane to distilled water releases the synemin and vimentin together in nearly pure form, before the release of significant amounts of spectrin and actin. These data suggest that avian erythrocyte intermeditate filaments are somehow anchored to the plasma membrane; erythrocytes may thus provide a simple system for the study of intermediate filaments and their mode of interaction with membranes. In addition, these data, in conjunction with previous data from muscle, indicate that synemin is capable of associating with either desmin or vimentin and may thus perform a special role in the structure or function of intermediate filaments in erythrocytes as well as muscle. 相似文献
90.
Roots regulate ion transport in the rhizosphere to counteract reduced mobility in dry soil 总被引:1,自引:0,他引:1
Diffusion of ions in the soil depends on soil moisture content. In a dry soil, transport of nutrients towards the root and the concomitant uptake could be reduced. However, pot and field experiments showed that this is not always the case. The objective of this paper was to investigate possible mechanisms of plants to counteract reduced nutrient supply due to water shortage. A split root system was used to investigate P and K inflow of oat and sugar beet at different soil moisture contents (Θ) without water shortage for the plant. The measured average P and K inflows were compared to model calculations considering diffusion, mass-flow, sorption and uptake processes. In the calculations, soil dryness impeded diffusion and decreased nutrient inflow as expected. Measured K inflow was decreased in a similar way indicating that Θ influences K diffusion. In contrast to this, measured P inflow was not influenced by Θ and under-estimated by the model. Low and high molecular exudates were collected at different water supply levels showing that exudation rate of both compounds was increased at water shortage. Especially the high molecular exudates (i.e. mainly mucilage) from water-stressed plants increased P concentration in soil solution under dry conditions in an incubation experiment. Calculated inflow considering this increased P concentration agreed well with measured P inflow indicating that exudation of mucilage could be a mechanism to overcome nutrient transport problems due to soil dryness. 相似文献