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1.
Indirect evidence suggests that legumes can adjust rapidly theresistance of their root nodules to O2 diffusion. Here we describeexperiments using O2 specific micro-electrodes and dark fieldmicroscopy to study directly the operation of this diffusionbarrier. The O2 concentration sensed by the electrode decreasedsharply in the region of the inner cortex and was less than1.0 mmol m3 throughout the infected tissue in nodulesof both pea (Pisum sativum) and french bean (Phaseolus vulgaris).In a number of experiments the ambient O2 concentration wasincreased to 40% while the electrode tip was just inside theinner cortex. In 13 out of 21 cases the O2 concentration atthis position either remained low and unchanged or increasedirreversibly to near ambient values. In the remaining casesthe O2 concentration increased after 1 to 2.5 min and then decreasedto its former value. These results are ascribed to an increasein resistance of the barrier in response to increased O2 fluxinto the nodule. It was shown microscopically that air spacesboth at the boundary between the infected zone and the innercortex, and within the infected zone started to disappear 3min after nodules were exposed to high ambient O2 concentrationsand had disappeared completely after 8 min. These spaces werenot changed by exposure of the nodule for 10 min to either N2or air. Key words: Oxygen, root nodules, air spaces 相似文献
2.
Evolution of the 28S ribosomal RNA gene in anurans: regions of variability and their phylogenetic implications 总被引:1,自引:0,他引:1
Fifteen restriction sites were mapped to the 28S ribosomal RNA gene of
individuals representing 54 species of frogs, two species of salamanders, a
caecilian, and a lungfish. Eight of these sites were present in all species
examined, and two were found in all but one species. Alignment of these
conserved restriction sites revealed, among anuran 28S rRNA genes, five
regions of major length variation that correspond to four of 12 previously
identified divergent domains of this gene. One of the divergent domains
(DD8) consists of two regions of length variation separated by a short
segment that is conserved at least throughout tetrapods. Most of the
insertions, deletions, and restriction-site variations identified in the
28S gene will require sequence-level analysis for a detailed reconstruction
of their history. However, an insertion in DD9 that is coextensive with
frogs in the suborder Neobatrachia, a BstEII site that is limited to
representatives of two leptodactylid subfamilies, and a deletion in DD10
that is found only in three ranoid genera are probably synapomorphies.
相似文献
3.
4.
Dual regulation of adenylate cyclase and guanylate cyclase: alpha 2-adrenergic signal transduction in adrenocortical carcinoma cells 总被引:1,自引:0,他引:1
Isolated adrenocortical carcinoma cells of rat contain alpha 2- and beta-adrenergic receptors. When these cells are incubated with alpha 2-adrenergic agonists, there is a concentration-dependent increase of cyclic GMP that is blocked by the alpha 2-adrenergic antagonist yohimbine but not by the beta-antagonist propranolol. Concomitantly, both p-aminoclonidine (20 microM) and clonidine (100 microM), the alpha 2-adrenergic agonists, stimulate membrane guanylate cyclase activity. In calcium free medium there is no alpha 2-agonist-dependent increase in cyclic GMP. Isoproterenol, a beta-agonist, and forskolin cause an increase in cyclic AMP but not cyclic GMP. The cyclic AMP increase induced by isoproterenol is blocked by propranolol but not by yohimbine. Isoproterenol- and forskolin-dependent increases in cyclic AMP are inhibited by p-aminoclonidine and the inhibition is relieved by yohimbine. These results indicate a dual regulation of guanylate cyclase and adenylate cyclase by the alpha 2-receptor signal: guanylate cyclase is coupled to the receptor in a positive fashion, whereas adenylate cyclase is coupled in a negative fashion. Calcium is obligatory in the cyclic GMP-mediated response. 相似文献
5.
Stem segments of adult plants of Ficus religiosa L. cultured on MS medium containing 1.0 mg/l 2,4-D produced callus. Shoots were regenerated when the induced calli were transferred to medium supplemented with 0.05 to 2.0 mg/l BAP. Callus derived shoots produced roots and developed into plantlets when transferred to medium supplemented with 1.0 mg/l NAA.Abbreviations MS
Murashige and Skoog (1962)
- BAP
6-benzylaminopurine
- NAA
naphthaleneacetic acid
- 2,4-D
2,4-dichlorophenoxyacetic acid 相似文献
6.
7.
8.
S. K. Jaiswal N. Hammatt S. S. Bhojwani E. C. Cocking M. R. Davey 《Plant Cell, Tissue and Organ Culture》1990,22(3):159-165
Protoplasts isolated from cotyledons of Brassica carinata, underwent sustained division when cultured at 5.0 × 104 ml-1 in modified 8p medium (KM8P) with 1.0% (w/v) Seaplaque agarose. Cell colonies produced callus when agarose droplets, in which the protoplasts were embedded, were transferred to K8 medium with 0.6% (w/v) Sigma Type I or Type VII agarose at day 16, giving a plating efficiency of 1.6%. Seventy percent of the protoplast derived-tissues produced shoot buds after subculture to MS medium containing 3.0% (w/v) sucrose, 1.125 mgl-1 BAP, 0.035 mgl-1 GA and 0.6% (w/v) Type I agarose, resulting in shoot formation from 1.1% of the protoplasts originally plated. Protoplast-derived colonies transferred to hormone-free MS medium with 1.0% (w/v) sucrose and 0.6% (w/v) Type I agarose produced roots. The latter gave rise to shoots after excision from the parent callus and culture on MS medium with 3.0% sucrose, 0.225 mgl-1 BAP, and 0.6% (w/v) Type I agarose. Shoots regenerated directly from protoplast-derived calli, or indirectly from roots, developed prolific root systems when placed on hormone-free MS medium with 1.0% (w/v) sucrose and 0.6% (w/v) Type I agarose.Abbreviations BAP
6-benzylaminopurine
- CH
casein hydrolysate
- 2,4-D
2,4-dichlorophenoxyacetic acid
- GA
gibberellic acid
- K
kinetin
- NAA
-naphthaleneacetic acid
- MES
2(N-morpholino)ethanesulphonic acid, 2,iP-6(,-dimethylallyamino) purine
- IAA
indole-3-acetic acid
- Z
zeatin
- ZR
zeatin riboside 相似文献
9.
Stefan Highsmith Mark Kubinec Devendra K. Jaiswal Hiromi Morimoto Philip G. Williams David E. Wemmer 《Journal of biomolecular NMR》1993,3(3):325-334
Summary The synthesis of [2-3H]ATP with specific activity high enough to use for 3H NMR spectroscopy at micromolar concentrations was accomplished by tritiodehalogenation of 2-Br-ATP. ATP with greater than 80% substitution at the 2-position and negligible tritium levels at other positions had a single 3H NMR peak at 8.20 ppm in 1D spectra obtained at 533 MHz. This result enables the application of tritium NMR spectroscopy to ATP utilizing enzymes.The proteolytic fragment of skeletal muscle myosin, called S1, consists of a heavy chain (95 kDa) and one alkali light chain (16 or 21 kDa) complex that retains myosin ATPase activity. In the presence of Mg2+, S1 converts [2-3H]ATP to [2-3H]ADP and the complex S1.Mg[2-3H]ADP has ADP bound in the active site. At 0°C, 1D 3H NMR spectra of S1.Mg[2-3H]ADP have two broadened peaks shifted 0.55 and 0.90 ppm upfield from the peak due to free [2-3H]ADP. Spectra with good signal-to-noise for 0.10 mM S1.Mg[2-3H]ADP were obtained in 180 min. The magnitude of the chemical shift caused by binding is consistent with the presence of an aromatic side chain being in the active site. Spectra were the same for S1 with either of the alkali light chains present, suggesting that the alkali light chains do not interact differently with the active site. The two broad peaks appear to be due to the two conformations of S1 that have been observed previously by other techniques. Raising the temperature to 20 °C causes small changes in the chemical shifts, narrows the peak widths from 150 to 80 Hz, and increases the relative area under the more upfield peak. Addition of orthovanadate (Vi) to produce S1.Mg[2-3H]ADP.Vi shifts both peaks slightly more upfield without chaning their widths or relative areas. 相似文献
10.
Human and animal mesenchymal progenitor cells from bone marrow: Identification of serum for optimal selection and proliferation 总被引:14,自引:0,他引:14
Donald P. Lennon Stephen E. Haynesworth Scott P. Bruder Neelam Jaiswal Arnold I. Caplan 《In vitro cellular & developmental biology. Animal》1996,32(10):602-611
Summary An undifferentiated subset of cells within the stromal cell population of bone marrow in postnatal mammals retains the capacity
to differentiate along osteogenic, adipogenic, fibroblastic, and chondrogenic lines. These cells, which are referred to as
mesenchymal stem cells (MSCs), can be maintainedin vitro and expanded in number through a process of subculturing. MSCs are maintained in culture in medium supplemented with 10%
fetal bovine serum (FBS). It is believed that certain, as yet unidentified, serum components play critical roles in the attachment
and proliferation of MSCs. Commercially available FBS is poorly characterized and may vary in composition and quality from
lot to lot. This study describes a method for the selection of lots of FBS that best support maintenance of the undifferentiated
state, mitotic expansion of MSCsin vitro, and retention of multilineage developmental potential in response to appropriate cues. 相似文献