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SYNOPSIS. The functional diversity of vertebrate skeletal musclelargely depends upon its structure. An important aspect of thisis its hierarchical design. At the cellular level, muscle fibersform three categories whose functional properties grade intoeach other: slow-oxidative fibers with high endurance to fatigue,fast-oxidative\glycolytic fibers also endurant but with greatermetabolic diversity, and fast-glycolytic fibers with limitedendurance but quick response. This partitioning of functionalproperties found among single muscle fibers is conserved ata second level of the structural hierarchy, since the groupof myofibers innervated by a single motor neuron (together calleda motor unit) is composed of the same fiber type. Differentmotor units may be recruited in an orderly pattern dependingupon the functional demands of a particular behavior. Finally,groups of motor units innervated by axons travelling togetherin the primary nerve branches may form discrete neuromuscularcompartments at a third level of structural hierarchy. Differentmotor units may be found in regional arrays in these compartmentsso that slow or fast units tend to be clumped together and maybe recruited together as larger functional units. This hierarchicalorganization of skeletal muscle may be a fundamental vertebrateplan that allows the diversity of functions so evident in vertebratebehavior. 相似文献
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LINDA C. IVANY STEPHEN C. PETERS BRUCE H. WILKINSON KYGER C. LOHMANN BETH A. REIMER 《Geobiology》2004,2(2):97-106
A sectioned and polished specimen of the coral Archohelia vicksburgensis from the early Oligocene Byram Formation (~30 Ma) near Vicksburg, Mississippi, reveals 12 prominent annual growth bands. Stable oxygen isotopic compositions of 77 growth‐band‐parallel microsamples of original aragonite exhibit well‐constrained fluctuations that range between ?2.0 and ?4.8. Variation in δ18O of coral carbonate reflects seasonal variation in temperature ranging from 12 to 24 °C about a mean of 18 °C. These values are consistent with those derived from a bivalve and a fish otolith from the same unit, each using independently derived palaeotemperature equations. Mg/Ca and Sr/Ca ratios were determined for 40 additional samples spanning five of the 12 annual bands. Palaeotemperatures calculated using elemental‐ratio thermometers calibrated on modern corals are consistently lower; mean temperature from Mg/Ca ratios are 12.5 ± 1 °C while those from Sr/Ca are 5.8 ± 2.2 °C. Assuming that δ18O‐derived temperatures are correct, relationships between temperature and elemental ratio for corals growing in today's ocean can be used to estimate Oligocene palaeoseawater Mg/Ca and Sr/Ca ratios. Calculations indicate that early Oligocene seawater Mg/Ca was ~81% (4.2 mol mol?1) and Sr/Ca ~109% (9.9 mmol mol?1) of modern values. Oligocene seawater with this degree of Mg depletion and Sr enrichment is in good agreement with that expected during the Palaeogene transition from ‘calcite’ to ‘aragonite’ seas. Lower Oligocene Mg/Ca probably reflects a decrease toward the present day in sea‐floor hydrothermal activity and concomitant decrease in scavenging of magnesium from seawater. Elevated Sr/Ca ratio may record lesser amounts of Oligocene aragonite precipitation and a correspondingly lower flux of strontium into the sedimentary carbonate reservoir than today. 相似文献
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OLGA V. TSYUSKO TRACEY D. TUBERVILLE MAUREEN B. PETERS NICHOLAS CRAWFORD CRIS HAGEN STEPHEN G. WELLER ANN K. SAKAI TRAVIS C. GLENN 《Molecular ecology resources》2007,7(6):1284-1286
Twelve polymorphic microsatellite loci were isolated from polyploid alpine wood‐sorrel, Oxalis alpina (Oxalidaceae), and optimized for future studies of its breeding system. The loci were screened for variability among 72 individuals from Pinos Altos, New Mexico. The primers amplified loci with allele number ranging from two to 17 per locus and with estimates of Nei's genetic diversity varying from 0.10 to 0.99. These primers provide an opportunity to use polymorphic DNA markers to study the causes of breeding system variability in this species. 相似文献
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MAAS FRANK M.; DE KOK LUIT J.; PETERS JANNY L.; KUIPER PIETER J. C. 《Journal of experimental botany》1987,38(9):1459-1469
Maas, F. M., De Kok, L. J., Peters, J. L. and Kuiper, P. J.C. 1987. A comparative study on the effects of H2S and SO2 fumigationon the growth and accumulation of sulphate and sulphydryl compoundsin Trifolium pratense L., Glycine max Merr. and Phaseolus vulgarisL.J. exp. Bot. 38: 1459-1469. The effects of 025 mm3 dm3 H2S and SO2 on growth andsulphur content of shoots of Trifolium pratense, Glycine maxand Phaseolus vulgaris were studied. After 2 weeks of fumigationthe yield of T. pralense was reduced by 32% by H2S, but notaffected by SO2. Yield of G. max was not affected by H2S, butreduced by 20% by SO2, whereas that of P. vulgaris was increasedby 11% by H2S and not affected by SO2. Increases in sulphydrylcontent were already observed after 24 h of exposure to H2Sand SO2 in all plants. The increase was greatest in T. pratenseand smallest in P. vulgaris and, except for T. pratense, alwaysgreater in the H2S-exposed than the SO2-exposed plants. Oneday of exposure resulted in an increase in sulphate contentonly in the SO2-fumigated plants, with the highest accumulationin T. pratense and the lowest in P. vulgaris. After 2 weeksan increase in sulphate content was also observed in the H2S-exposedplants. This increase was also highest in T. pratense and lowestin P. vulgaris. Transpiration rate was not affected by a 24 h exposure to H2Sor SO2 and was highest in T. pratense, intermediate in G. maxand lowest in P. vulgaris. The order of theoretical rates of deposition of H2S and SO2correlated with the observed increases in sulphydryl contentduring the first 24 h of exposure in both H2S and SO2-fumigatedplants and with the increase in sulphate content in the SO2-exposedplants. The increases in sulphydryl content were only 8% ofthe theoretical H2S and SO2-deposition fluxes, whereas sulphateaccumulation accounted for at least 57% of the theoretical SO2-depositionflux. Key words: Air pollution, clover, French bean, Glutathione, Soybean, sulphur metabolism. 相似文献
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