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41.
42.
Summary Histochemical studies of the opercularis muscle of the bullfrog (Rana catesbeiana) and the tiger salamander (Ambystoma tigrinum) provide evidence that the opercularis muscle of anurans is a specialized, tonic portion of the levator scapulae superior muscle. Staining results for myosin adenosine triphosphatase (ATPase) and succinate dehydrogenase (SDH), combined with measurements of muscle fiber diameters, demonstrate that the opercularis/levator scapulae superior muscle mass of both the tiger salamander and bullfrog consists of an anterior tonic portion, a middle fast oxidative-glycolytic (FOG) twitch portion, and a posterior fast-glycolytic (FG) twitch portion. In R. catesbeiana the tonic fibers represent 57.3% of the fiber total and (because they have relatively narrow diameters) about 29% of the cross-sectional area of the muscle mass, and form that part of the muscle (=opercularis muscle) that inserts on the operculum. In Ambystoma the tonic fibers represent only 8.8% of the fiber total and represent about 4% of the cross-sectional area. In the tiger salamander, the entire levator scapulae superior muscle inserts on the operculum and therefore represents the opercularis muscle. The bullfrog differs from the tiger salamander, therefore, in that the anterior tonic part of the opercularis/levator scapulae superior complex is greatly enlarged and the insertion on the operculum is limited to these tonic fibers. No evidence of a columellar muscle was found in R. catesbeiana. Previous reports of one in this species and in other anurans may be based on the tripartite nature of the opercularis/levator scapulae superior muscle mass. The middle FOG portion of the muscle may have been considered a muscle distinct from the anterior tonic portion (=opercularis muscle) and the posterior FG portion. 相似文献
43.
Ice Encasement Injury to Microsomal Membranes from Winter Wheat Crowns : I. Comparison of Membrane Properties after Lethal Ice Encasement and during a Post-Thaw Period 总被引:2,自引:1,他引:1 下载免费PDF全文
The functional and physical properties of cellular membranes isolated from Triticum aestivum, cvs Norstar and Fredrick, were altered coincident with changes in composition after a lethal ice-encasement stress and further during a 6 hour post-thaw period. Crowns encased in ice for a duration which inhibited regrowth, exhibited enhanced rates of electrolyte leakage. Furthermore, the recovery of total microsomal protein and phospholipid declined, suggesting that some membrane degradation had been induced during the anoxic stress. The microviscosity of microsomes and liposomes prepared from such membranes increased during stress, and this was correlated with a 2- to 4-fold increase in the free fatty acid levels in the microsomal fraction. There was, however, only a relatively minor change in fatty acid unsaturation during the ice-encasement stress. The process continued during a 6 hour aerobic post-thaw treatment, but the pattern was somewhat different. During this phase, the leakage of electrolytes was further increased and the recovery of microsomal protein and phospholipid continued to decline, indicating general degradation; but, in contrast to the anoxic phase, the degree of fatty acid unsaturation declined markedly, indicating lipid peroxidation. 相似文献
44.
Stress tolerance and stress-induced injury in crop plants measured by chlorophyll fluorescence in vivo: chilling, freezing, ice cover, heat, and high light 总被引:10,自引:5,他引:5 下载免费PDF全文
The proposition is examined that measurements of chlorophyll fluorescence in vivo can be used to monitor cellular injury caused by environmental stresses rapidly and nondestructively and to determine the relative stress tolerances of different species. Stress responses of leaf tissue were measured by FR, the maximal rate of the induced rise in chlorophyll fluorescence. The time taken for FR to decrease by 50% in leaves at 0°C was used as a measure of chilling tolerance. This value was 4.3 hours for chilling-sensitive cucumber. In contrast, FR decreased very slowly in cucumber leaves at 10°C or in chilling-tolerant cabbage leaves at 0°C. Long-term changes in FR of barley, wheat, and rye leaves kept at 0°C were different in frost-hardened and unhardened material and in the latter appeared to be correlated to plant frost tolerance. To simulate damage caused by a thick ice cover, wheat leaves were placed at 0°C under N2. Kharkov wheat, a variety tolerant of ice encapsulation, showed a slower decrease in FR than Gatcher, a spring wheat. Relative heat tolerance was also indicated by the decrease in FR in heated leaves while changes in vivo resulting from photoinhibition, ultraviolet radiation, and photobleaching can also be measured. 相似文献
45.
Howard Griffiths Mark S. J. Broadmeadow Anne M. Borland Clive S. Hetherington 《Planta》1990,181(4):604-610
Short-term measurements of instantaneous carbon-isotope discrimination have been determined from mass-spectrometric analyses of CO2 collected online during gas exchange for the epiphytic bromeliad Tillandsia utriculata L. Using this technique, the isotopic signature of CO2 exchange for each phase of Crassulacean acid metabolism (CAM) has been characterised. During night-time fixation of CO2 (Phase I), discrimination () ranged from 4.4 to 6.6, equivalent to an effective carbon-isotope ratio (13C) of –12.3 to –14.5 versus Pee Dee Belemnite (PDB). These values reflected the gross photosynthetic balance between net CO2 uptake and refixation of respiratory CO2, characteristic of CAM in the Bromeliaceae. When for the relative proportion of external (p
a
) and internal (p
i) CO2 is taken into account, calculated p
i/p
a decreased during the later part of the dark period from 0.68 to 0.48. Measurements of during Phase II, early in the light period, showed the transition between C4 and C3 pathways, with carboxylation being increasingly dominated by ribulose bisphosphate carboxylase (Rubisco) as increased from 10.5 to 21.2 During decarboxylation in the light period (Phase III), CO2 leaked out of the leaf and the inherent discrimination of Rubisco was expressed. The value of calculated from on-line measurements (64.4) showed that the CO2 lost was considerably enriched in 13C, and this was confirmed by direct analysis of the CO2 diffusing out into a CO2-free atmosphere (
13C = + 51.6 versus PDB). Instantaneous discrimination was characteristic of the C3 pathway during Phase IV (late in the light period), but a reduction in showed an increasing contribution from phosphoenolpyruvate carboxylase. The results from this non-invasive technique confirm the observations that double carboxylation involving both phosphoenolpyruvate carboxylase and Rubisco occurs during the transient phases of CAM (II and IV) in the light period.Abbreviations and Symbols CAM
Crassulacean acid metabolism
-
H+
(dawn-dusk) variation in titratable acidity
-
13C
carbonisotope ratio of plant organic material, relative to Pee Dee Belemnite (vs. PDB)
-
discrimination against 13CO2,
-
p
i, p
a
internal, external partial pressures of CO2
- Rubisco
ribulose1,5-bisphosphate carboxylase
- PAR
photosynthetically active radiation
- PEPCase
phosphoenolpyruvate carboxylase
We are grateful for financial support in respect of research grants (GR3/5360, GR3/6419) and a studentship awarded by the Natural Environment Research Council, UK. 相似文献
46.
The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs. 相似文献
47.
Yvet E Noordman Patrick AM Jansen Wiljan JAJ Hendriks 《Journal of molecular signaling》2006,1(1):1-11
Background
Spatio-temporal control of extracellular signal-regulated kinase (ERK) activity, a critical determinant of the cell's response to growth factors, requires timely dephosphorylation of its regulatory tyrosine and/or threonine residue by MAPK phosphatases. We studied the physiological role of kinase interaction motif (KIM)-containing protein tyrosine phosphatases (PTPs) in the control of EGF- and NGF-induced ERK activity in neuroendocrine PC12 cells.Results
We found a single KIM-containing PTP to be endogenously expressed in rat PC12 cells: the transmembrane PTPRR isoform termed PCPTP1. Protein knock-down of PCPTP1, or fourfold overexpression of its mouse orthologue, PTPBR7, left EGF- and NGF-induced ERK1/2 activity in PC12 cells unaltered. Ectopic expression of cytosolic PTPRR isoforms, however, resulted in reduced EGF-induced ERK1/2 activity, an effect that was dependent on the phosphatase activity and the KIM-domain of these PTPs.Conclusion
The finding that robust changes in tyrosine-specific MAPK phosphatase expression levels have minor effects on temporal ERK1/2 activity control in PC12 cells suggests that dual-specificity MAPK phosphatases may act as major regulators of growth factor-induced ERK1/2 signaling in these cells. 相似文献48.
The use of Arabidopsis mutants defective in abscisic acid (ABA) perception has been instrumental in the understanding of stomatal function, in particular, ABA signalling in guard cells. The considerable attention devoted to ABA signalling in guard cells is due in part to (1) the fundamental role of ABA in drought stress and (2) the use of a screening protocol based on the sensitivity of seed germination to ABA. Such a screen has facilitated the isolation of ABA signalling mutants with genetic lesions that exert pleiotropic effects at the whole plant level. As such, there is a requirement for new approaches to complement the seed germination screen. The recent advances made in the use of infrared thermography as a non-invasive, high-throughput tool are reviewed here and the versatility of this technique for screening Arabidopsis defective in stomatal regulation is highlighted. 相似文献
49.
Saccharomyces paradoxus is the closest known relative of the well-known S. cerevisiae and an attractive model organism for population genetic and genomic studies. Here we characterize a set of 28 wild isolates from a 10-km(2) sampling area in southern England. All 28 isolates are homothallic (capable of mating-type switching) and wild type with respect to nutrient requirements. Nine wild isolates and two lab strains of S. paradoxus were surveyed for sequence variation at six loci totaling 7 kb, and all 28 wild isolates were then genotyped at seven polymorphic loci. These data were used to calculate nucleotide diversity and number of segregating sites in S. paradoxus and to investigate geographic differentiation, population structure, and linkage disequilibrium. Synonymous site diversity is approximately 0.3%. Extensive incompatibilities between gene genealogies indicate frequent recombination between unlinked loci, but there is no evidence of recombination within genes. Some localized clonal growth is apparent. The frequency of outcrossing relative to inbreeding is estimated at 1.1% on the basis of heterozygosity. Thus, all three modes of reproduction known in the lab (clonal replication, inbreeding, and outcrossing) have been important in molding genetic variation in this species. 相似文献
50.
ABA-regulated promoter activity in stomatal guard cells 总被引:4,自引:0,他引:4
Jane E. Taylor Kirstie F. Renwick Alex A.R. Webb Martin R. McAinsh Antonella Furini Dorothea Bartels Ralph S. Quatrano William R. Marcotte Jr. Alistair M. Hetherington 《The Plant journal : for cell and molecular biology》1995,7(1):129-134
CDeT6-19 is an ABA-regulated gene which has been isolated from Craterostigma plantagineum . The CDeT6-19 gene promoter has been fused to the β- glucuronidase reporter gene ( GUS ) and used to stably transform Arabidopsis thaliana and Nicotiana tabacum . This construct has been shown to be expressed in stomatal guard cells and often in the adjacent epidermal cells of both species in response to both exogenous ABA and drought stress. These results indicate that the stomatal guard cell is competent to relay an ABA signal to the nucleus. In contrast GUS expression directed by the promoter from a predominantly seed-specific, ABA-regulated gene, Em , or the promoter from the ABA-regulated CDeT27-45 gene is not detectable in the epidermal or guard cells of tobacco or Arabidopsis in response to ABA. The fact that not all ABA-regulated gene promoters are active in stomatal guard cells suggests that effective transduction of the signal is dependent upon particular regions within the gene promoter or that guard cells lack all or part of the specific transduction apparatus required to couple the ABA signal to these promoters. This suggests that there are multiple ABA stimulus response coupling pathways. The identification of a regulatory sequence from an ABA-induced gene which is expressed in stomatal guard cells creates the possibility of examining the role of Ca2+ and other second messengers in ABA-induced gene expression. 相似文献