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1.
Orientation dependence and rotational motion of maleimide spin labels attached to the fast reacting thiol sites of myosin were studied in glycerinated cardiac and skeletal muscle fibres in rigor and in relaxing medium. The probe order in skeletal muscle was shown to be about one order of magnitude higher than that in cardiac muscle. In skeletal muscle in rigor the orientational order is static on the time scale of the saturation transfer electron paramagnetic resonance measurement (ST EPR, rotational correlation time of the label is greater than 1 ms), but in cardiac muscle fibres, a disorder was observed which was at least partly dynamical, the rotational correlation time being about 100 microseconds. In relaxing solution the degree of order of probe molecules in both types of muscle was strongly reduced at and above the resting length. The disorder was at least partly dynamical on the ST EPR time scale, the apparent rotational correlation times being 200 microseconds for skeletal muscle and 60 microseconds for cardiac muscle, respectively. According to the results of ST EPR the rotational behavior of cross-bridges was identical in cardiac and skeletal muscle in relaxing medium. 相似文献
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From the cambial stage onwards, the symplasmic autonomy of sieve element/companion cell complexes (SE/CC-complexes) was followed in stems of Lupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intracellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multicellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.Abbreviations LYCH
Lucifer Yellow CH
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membrane potential
- PMF
proton-motive force
- PP
phloem parenchyma cell
- SE/CC-complex
sieve element/companion cell complex
- SR-G
sulphorhodamine G 相似文献
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Mario Rincón-Barrado Sanna Olsson Tamara Villaverde Belén Moncalvillo Lisa Pokorny Alan Forrest Ricarda Riina Isabel Sanmartín 《植物分类学报:英文版》2021,59(5):915-934
Wide-range geographically discontinuous distributions have long intrigued scientists. We explore the role of ecology, geology, and dispersal in the formation of these large-scale disjunctions, using the angiosperm tribe Putorieae (Rubiaceae) as a case study. From DNA sequences of nuclear ITS and six plastid markers, we inferred a phylogeny with 65% of all known Putorieae species. Divergence times, ancestral ranges, and diversification rate shifts were then estimated using Bayesian inference. We further explored species climatic tolerances and performed ancestral niche reconstruction to discriminate among alternative speciation modes, including geographical and ecological vicariance, and ecogeographical, ecological, and dispersal-mediated speciation. As a result, we identified seven major clades in Putorieae, some of which exhibit striking geographical disjunctions, matching the Rand Flora pattern, with sister species in the Canary Islands andeastern and southern Africa. Initial diversification within the tribe occurred in the early Miocene, coincident with a period of climate warming; however, most clades diverged within the last 10 Myr. Aridification and high extinction rates, coupled with ecological vicariance, explain the oldest disjunctions. Adaptation to new environmental conditions, after allopatry, is observed in several clades. Dispersal, either long-distance or via corridors made available by mountain uplift, is behind the most recent disjunctions. Some of these events were followed by ecological speciation and rapid diversification, with species becoming adapted to xeric or increasingly colder continental climates. We show that an integrative approach may help discriminate among speciation modes invoked to explain disjunctions at macroevolutionary time scales, even when extinction has erased the signature of past events. 相似文献
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Margarita Pérez-Jiménez M. Belén López-Soto José Cos-Terrer 《In vitro cellular & developmental biology. Plant》2013,49(1):79-84
We describe an efficient protocol for callus induction from adult tissues of Prunus persica (L.) Batsch. Three different commercial peach genotypes, Early May®, Zise May®, and UFO-3®, plus three other genotypes from hybrid crosses performed in February 2006, PS108, PS208, and PS708, were used in the study. Thirteen explant treatments were tested using nine different plant parts. Murashige and Skoog and woody plant medium salts were assayed with several concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), kinetin (KN), and thidiazuron, and two different photoperiods were tested, a 16-h photoperiod or continuous darkness. In terms of the quantitative response, two parameters were assessed: the number of d to callus induction and relative callus growth recorded after 30 d. Woody plant medium supplemented with 2,4-D and KN significantly increased the rates of callus induction in the majority of treatments. And no significant differences among the P. persica genotypes were found. The explants derived from stem and calyx produced up to 85 and 96% callus induction, respectively. The protocol described here could be used for efficient callus induction in a range of Prunus spp. 相似文献
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K. A. Razumova V. F. Andreev I. S. Bel’bas A. V. Gorshkov A. Yu. Dnestrovskij K. S. Dyabilin A. Ya. Kislov S. E. Lysenko G. E. Notkin N. N. Timchenko A. N. Chudnovskiy D. A. Shelukhin 《Plasma Physics Reports》2013,39(9):691-697
Results are presented from experiments on the formation of an internal electron transport barrier near the q = 1.5 rational surface in the T-10 tokamak. The experiments were carried out in the regime with off-axis electron cyclotron resonance (ECR) heating followed by a fast plasma current ramp-up. After suppressing sawtooth oscillations by off-axis ECR heating, an internal transport barrier began to form near the q = 1.5 rational surface. In the phase of the current ramp-up, the quality of the transport barrier improved; as a result, the plasma energy confinement time increased 2–2.5 times. The intentionally produced flattening of the profile of the safety factor q(r) insignificantly affected magnetohydrodynamic activity in the plasma column in spite of the theoretical possibility of formation of substantial m/n = 3/2 and 2/1 magnetic islands. Conditions are discussed under which the flattening of the profile of the safety factor q near low-order rational surfaces leads to the formation of either an internal transport barrier or the development of an island magnetic structure induced by tearing modes. 相似文献
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The parasitism (Hymenoptera, Braconidae, Aphidiinae) of alfalfa aphids (Hemiptera, Aphididae) was determined during three crop growing seasons. The highest rates of parasitism of Acyrthosiphon pisum Harris and of Therioaphis trifolii Monell occurred during the first-second and the fourth alfalfa intercuts, respectively. The landscape surrounding the fields affected only parasitism rates of A. pisum. During the second intercut the forest area had a negative influence on parasitism rates, whereas the bordering surfaces of alfalfa and winter cereals had a positive influence. Positive correlations were found between the rates of parasitism of A. pisum and the rate of aphid population increase in the first intercut. By contrast, negative correlations were found in the second intercut, when the aphid population peaked, suggesting that parasitoids contribute to the regulation of the aphid. This study stresses that regulation of alfalfa aphids cannot be explained solely on the basis of one functional group of natural enemies. 相似文献