Multiple genotypes of mitochondrial DNA within a horse population from a small region in Yunnan province of China

mtDNA genotypes of six domestic horses (three adult short horses whose heights are under 1 m and three common domestic horses) from a small region of 15 km² in Malipo county of Yunnan province of China were investigated by the technique of restriction fragment length polymorphism (RFLP) with 16 restriction endonucleases which recognize 6-bp sequences. An average of 56 fragments for an individual was obtained. Unlike other domestic animals, this population of horses exhibits high mtDNA genetic diversity. Each of the six horses has a specific mtDNA genotype showing a pattern of multiple maternal origins, as suggested by fossil and literature records. We think the population of horses is an amazing seed-resource pool of horses and hence deserves to be paid more attention from the view of conservation genetics. However, it is also remarkable that we did not find any typical mtDNA genetic markers which would discriminate between short horses and common domestic horses.     

De novo synthesis of thymidylate via deoxycytidine in dcd (dCTP deaminase) mutants of Escherichia coli.

dcd (dCTP deaminase) mutants of Escherichia coli were reported not to require thymidine for growth even though most of the thymidylate that is synthesized de novo arises from cytosine nucleotides through a pathway involving dCTP deaminase. We found, however, that the fresh introduction of dcd mutations into many strains of E. coli produced a requirement for thymidine for optimum aerobic growth, but the mutants readily reverted to prototrophy via mutations in other genes. One such mutation was in deoA, the gene for deoxyuridine phosphorylase. However, a dcd deo mutant became thymidine dependent once again if a cdd mutation (affecting deoxycytidine deaminase) were introduced. The results indicate that dcd mutants utilize an alternative pathway of TMP synthesis in which deoxycytidine and deoxyuridine are intermediates. A cdd mutation blocks the pathway by preventing the conversion of deoxycytidine to deoxyuridine, whereas a deoA mutation enhances it by sparing deoxyuridine from catabolism. The deoxycytidine must arise from dCTP or dCDP via unknown steps. It is not known to what extent this pathway is utilized in wild-type cells, which, unlike the dcd mutants, do not accumulate dCTP.     

Water potentials for developing cladodes and fruits of a succulent plant, including xylem-versus-phloem implications for water movement

Developing cladodes had lower water potentials and developingfruits had higher water potentials than the underlying cladodesof the widely cultivated prickly pear cactus, Opuntia ficus-indica.The 0.06 MPa lower value in 4-week-old daughter cladodes indicateda typical water potential gradient from the underlying clad-odealong the xylem of –0.2 MPa m^–1; the 0.17 MPa highervalue in 4-week-old fruits, which decreased to 0.07 MPa by 10weeks, implicated the phloem as their supplier of water. Thephloem sap of the underlying cladodes had an osmotic pressureof only 0.90 to 0.98 MPa, so the phloem could supply a relativelydilute solution to the photosynthetically dependent fruits (daughtercladodes of O. ficus-indica are photosynthetically independentat 4 weeks). Although the water potentials were similar foradjacent tissues, the osmotic pressures were lower for the water-storagecompared with the photosynthetic tissue; the osmotic pressureswere higher for xylem sap from fruits, for which xylary flowapparently occurred toward the underlying cladodes, than fordaughter cladodes. The relative capacitance (change in relativewater content divided by change in tissue water potential) wasapproximately 0.71 MPa^–1 for the water-storage tissueand the photosynthetic tissue of both daughter cladodes andfruits at 4 weeks of age. When these organs approached maturityat 10 weeks, the relative capacitance increased about 40% fortheir water-storage tissue, but decreased 30% for their photosynthetictissue. As the plant water content decreases during drought,about twice as much water will thus be lost per unit volumeof the water-storage tissue compared with the photosynthetictissue of maturing fruits and cladodes. Key words: Opuntia ficus-indica, phloem, relative water content, water capacitance, water potential     

Effects of substratum morphology on cell physiology

Among the host of substratum properties that affect animal cell behavior, surface morphology has received relatively little attention. The earliest effect of surface morphology on animal cells was discovered almost a century ago when it was found that cells became oriented in response to the underlying topography. This phenomenon is now commonly known as contact guidance. From then until very recentrly, little progress has been made in understanding the role of surface morphology on cell behavior, primarily due to a lack of defined surfaces with uniform morphologies. This problem has been solved recently with the development of photolithographic techniques to prepare substrata with well defined and uniform surface morphologies. Availability of such surfaces has facilitated systematic in vitro experiments to study influence of surface morphology on diverse cell physiological aspects such as adhesion, growth, and function. For example, these studies have shown that surfaces with uniform multipls parallel grooves can enhance cell adhesion by confining cells in grooves and by mechanically interlocking them. Several independent studies have demosterated that cell shape is a major determinant of cell growth and function. Because surface morphology has been shown to modulate the extent of cell spreading and cell shape, its effects on cell growth and function appear to be mediated via this biological coupling between cell shape and function. New evidence in the cell biology literature is emerging to suggest that surface morphology could affect other cell behavioral properties such as post-translational modifications. Further elucidation of such effects will enable better designs for implant and cell culture substrata.     

Vibrational circular dichroism of A-, B-, and Z-form nucleic acids in the PO2-stretching region.

Vibrational circular dichroism (VCD) spectra were measured for H2O solutions of several natural and model DNAs (single and double strands, oligomers and polymers) in the B-form, poly(dG-dC)-poly(dG-dC) in the Z-form, and various duplex RNAs in an A-form over the PO2-stretching region. Only the symmetric PO2 stretch at approximately 1075 cm-1 yields a significant intensity VCD signal. Differences of the PO2-stretching VCD spectra found for these conformational types are consistent with the spectral changes seen in the base region, but no sequence dependence was seen in contrast to VCD for base modes. The B to Z transition is accompanied by an inversion of the PO2- VCD spectra, which is characteristic of the change in the helical sense of the nucleic acid backbone. A-RNAs give rise to the same sense of couplet VCD as do B-DNAs but have a somewhat different shape because of overlapping ribose modes. These PO2- VCD spectral characteristics have been successfully modeled using simple dipole coupling calculations. The invariability of the symmetric PO2- stretching mode VCD spectra to the base sequence as opposed to that found for the C = O stretching and base deformation modes is evidence that this mode will provide a stable indication of the DNA helical sense.     

Absence of effects of low-frequency, low-amplitude magnetic fields on the properties of gramicidin A channels.

The effects of static and low-frequency magnetic fields on gramicidin A channels have been investigated using bilayer patch clamp recording and a bridge technique capable of detecting 0.3% changes in the conductance of glyceryl monooleate membranes containing many channels. In the bridge technique the conductance was assessed using 10-ms voltage pulses applied at 10 Hz. Measurements were made for LiCl, KCl, and CsCl using magnetic fields of 50, 100, 500, and 5000 microT with the frequency scanned from 10-200 Hz. The combinations of static and low-frequency fields employed include the "cyclotron resonance" conditions at which effects had been predicted to occur. In no case was there any detectable change in conductance when the magnetic fields were applied or changed. Potassium currents through single gramicidin channels have been recorded for patches in which several channels may be open at once. Fields were applied for 2 min periods interleaved with 2 min controls. Methods have been developed to analyze the multichannel records to reveal the amplitude and duration of the channels together with the frequency, depth, and apparent period of flickers. No significant differences were observed between the control and field-exposed recording periods. The peak of the distribution of opening and closing transitions always coincided for fields on and off within the resolution, 0.4%, of the recordings. There are at least two types of flicker, one with typical period less than 0.1 ms, the other with typical period from 0.3-0.8 ms. Most of the latter were not complete closures with the conductance during a flicker 15-20% above the level for a full closure.     

Saturated Molecular Map of the Rice Genome Based on an Interspecific Backcross Population

A molecular map has been constructed for the rice genome comprised of 726 markers (mainly restriction fragment length polymorphisms; RFLPs). The mapping population was derived from a backcross between cultivated rice, Oryza sativa, and its wild African relative, Oryza longistaminata. The very high level of polymorphism between these species, combined with the use of polymerase chain reaction-amplified cDNA libraries, contributed to mapping efficiency. A subset of the probes used in this study was previously used to construct an RFLP map derived from an inter subspecific cross, providing a basis for comparison of the two maps and of the relative mapping efficiencies in the two crosses. In addition to the previously described PstI genomic rice library, three cDNA libraries from rice (Oryza), oat (Avena) and barley (Hordeum) were used in this mapping project. Levels of polymorphism detected by each and the frequency of identifying heterologous sequences for use in rice mapping are discussed. Though strong reproductive barriers isolate O. sativa from O. longistaminata, the percentage of markers showing distorted segregation in this backcross population was not significantly different than that observed in an intraspecific F(2) population previously used for mapping. The map contains 1491 cM with an average interval size of 4.0 cM on the framework map, and 2.0 cM overall. A total of 238 markers from the previously described PstI genomic rice library, 250 markers from a cDNA library of rice (Oryza), 112 cDNA markers from oat (Avena), and 20 cDNA markers from a barley (Hordeum) library, two genomic clones from maize (Zea), 11 microsatellite markers, three telomere markers, eleven isozymes, 26 cloned genes, six RAPD, and 47 mutant phenotypes were used in this mapping project. Applications of a molecular map for plant improvement are discussed.     

Variations in Immune Response of Popillia japonica and Acheta domesticus to Heterorhabditis bacteriophora and Steinernema Species

The infectivities of Steinernema carpocapsae, S. glaseri, S. scapterisci, and Heterorhabditis bacteriophora to Japanese beetle larvae, Popillia japonica, and house cricket adults, Acheta domesticus, were compared using external exposure and hemocoelic injection. Only H. bacteriophora and S. glaseri caused high P. japonica mortality after external exposure. When nematodes were injected, P. japonica had a strong encapsulation and melanization response to all species except S. glaseri. Heterorhabditis bacteriophora and S. carpocapsae were able to overcome the immune response, but S. scapterisci was not. All species except S. scapterisci were able to kill and reproduce within the host. Only S. scapterisci and S. carpocapsae caused A. domesticus mortality after external exposure. When nematodes were injected, A. domesticus had a strong immune response to all species except S. scapterisci. Steinernema carpocapsae effectively overcame the strong immune response and caused high host mortality, but S. glaseri and H. bacteriophora did not. Steinernema scapterisci caused high host mortality and reproduced, S. glaseri and H. bacteriophora caused low host mortality but only S. glaseri reproduced, and S. carpocapsae was able to kill the host but reproduced poorly. Most (ca. 90%) of the S. carpocapsae in the hemocoel of P. japonica became encapsulated and melanized within 8 hours postinjection. The symbiotic bacterium, Xenorhabduf nematophilus, was often released before this encapsulation and melanization.     

Induction of Nitric Oxide Synthase in Rat C6 Glioma Cells

Abstract: We have examined the induction of nitric oxide syhthase (NOS) activity in the rat astrocyte-derived C6 glioma cell line. In contrast to the previous results with primary astrocyte cultures, incubation of C6 cells with bacterial endotoxin lipopolysaccharide (LPS; 1 μg/ml for 24 h) did not stimulate NO₂ production. However, addition of either tumor necrosis factor-a (TNF-α) or interferon-γ (IFN-γ), cytokines that by themselves had no effect on NOS activity, imparted LPS responsiveness onto these cells in a dose-dependent manner (EC₅₀ values of 39 ng/ml of TNF-α and 9.4 U/ml of IFN-γ), and the effect of TNF-α could be further potentiated (twofold) by the presence of interleukin-1β. The simultaneous presence of TNF-α and IFN-γ yielded a greater response than either cytokine alone; however, the respective EC₅₀ values were not affected. A cytoplasmic extract from induced C6 cells catalyzed the Ca²⁺-independent conversion of l -arginine to l - citrulline, with an apparent K _m of 51.2 n M , and this activity could be blocked by l -arginine analogues in the potency order amino > methyl > nitroarginine. Immunoblot analysis revealed an apparent molecular mass of 125 kDa for the NOS protein induced in C6 cells. These results indicate that the combination of LPS plus cytokines can induce NOS activity in C6 glioma cells with properties similar to those of the enzyme expressed in primary astrocyte cultures.