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  • 2000-2004  (175)
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  • 1
    ISSN: 1570-7458
    Keywords: Lepidoptera ; Tortricidae ; reproduction ; tebufenozide ; methoxyfenozide ; ecdysone agonist ; Argyrotaenia velutinana ; Choristoneura rosaceana
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects on the fecundity and fertility of redbanded leafroller, Argyrotaenia velutinana (Walker), and obliquebanded leafroller,Choristoneura rosaceana (Harris), exposed as adults to surfaces treated with the ecdysone agonists tebufenozide (RH-5992) and methoxyfenozide (RH-2485) were examined. The first part of the study consisted of recently emerged moths being exposed to treated surfaces continuously throughout their lives (including mating and oviposition). Continuous exposure to tebufenozide- or methoxyfenozide-treated surfaces significantly reduced the mean number of eggs laid and the percent of eggs that hatched in both species. The second part of the study involved exposure of recently emerged virgin moths (by sex) to treated surfaces for 24 h, after which, the exposed moths were paired with a nontreated partner to mate and oviposit on nontreated surfaces. In this experiment, for A. velutinana, significant reductions in fecundity occurred only when the female was exposed to methoxyfenozide-treated surfaces. Significant reductions in A. velutinana egg fertility occurred with both male and female exposure in the methoxyfenozide treatments and only female exposure in the tebufenozide treatments. For C. rosaceana, significant reductions in fecundity occurred with both male and female exposure in the tebufenozide and methoxyfenozide treatments. Significant reductions in C. rosaceana egg fertility occurred with both male and female exposure in the tebufenozide treatments and only with female exposure in the methoxyfenozide treatments.
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  • 2
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    Entomologia experimentalis et applicata 95 (2000), S. 217-227 
    ISSN: 1570-7458
    Keywords: antifeedant ; drimane ; mechanism of action ; sensory response ; toxicity ; habituation ; behavioural observation ; structure-activity relationship ; Pieris brassicae ; Lepidoptera ; Pieridae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We tested 11 analogous synthetic drimane antifeedant compounds for their feeding inhibiting effects on larvae of the large white butterfly Pieris brassicae L. (Lepidoptera: Pieridae) in no-choice tests on the host plant Brassica oleracea L. Furthermore, we observed larval feeding behaviour in no-choice tests to analyze temporal effects of five drimanes. The results show that the five analogous antifeedants differentially influence feeding behaviour and locomotion activity. Warburganal and polygodial are most likely sensory mediated antifeedants. Habituation to these compounds occurs soon after the onset of the tests (i.e., within 0.5–1.5 h). Compound 5 and confertifolin are probably not direct, sensory mediated antifeedants. After 0.5–1.5 h of exposure, these compounds inhibit not only feeding, but also locomotion behaviour, indicating postingestive, toxic effects. Isodrimenin inhibits feeding from the onset of the test and is probably a sensory mediated antifeedant. No habituation occurs to this compound, indicating that isodrimenin is either a very strong antifeedant or that it additionally has postingestive, toxic effects. Topical application of the drimanes on the larval cuticle revealed feeding inhibiting effects, but these could not be related to the occurrence of postingestive feeding inhibiting effects, indicating that this method is inappropriate to show possible postingestive effects of drimanes in P. brassicae. In conclusion, the behavioural observations performed in this research indicate that analogous drimanes inhibit feeding by P. brassicae larvae through multiple mechanisms of action. The results show that, when developing a structure activity relationship (SAR) for a series of antifeedants, it is important to distinguish the mode of action which underlies inhibition of feeding.
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  • 3
    ISSN: 1570-7458
    Keywords: Cnaphalocrocis medinalis ; rice leaffolder ; Lepidoptera ; Pyralidae ; sex pheromone ; geographical variation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sex pheromone components of the Japanese rice leaffolder moth, Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) were identified from ovipositor extracts of virgin females as (Z)-11-octadecenal, (Z)-13-octadecenal, (Z)-11-octadecen-1-ol and (Z)-13-octadecen-1-ol at a ratio of 11:100:24:36 by GC-EAD, GC, GC-MS. The total amount was estimated to be ca.0.9 ng/female. Field bioassays in Kagoshima, Japan, showed that the two aldehydes are essential for male attraction and the alcohols may have a synergistic effect on the aldehydes. A rubber septum containing 0.9 mg of the four components at the natural ratio was shown to be an effective lure for monitoring this pest in Japan. The above four components are quite different from the sex pheromone components reported previously for the same species of either Philippine or Indian origin; components were shown to be (Z)-11-hexadecenyl acetate and (Z)-13-octadecenyl acetate at a ratio of 98:2 in the Philippine blend and 1:10 in the Indian blend. Furthermore, in the field tests in Japan, neither the Philippine blend nor the Indian blend showed any attractive activity, while the Japanese blend attracted significant numbers of male moths. These results suggest that there are remarkable geographical variations in the sex pheromone composition of this species or there are several distinct species using different sex pheromone blends.
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  • 4
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    Entomologia experimentalis et applicata 97 (2000), S. 137-147 
    ISSN: 1570-7458
    Keywords: Etiella zinckenella ; Etiella hobsoni ; Lepidoptera ; Pyralidae ; soybean ; development ; reproduction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Experiments conducted in West Java, Indonesia investigated the developmental biology and reproductive behavior of two sympatric soybean pod borers, Etiella zinckenella Treitschke and E. hobsoni Butler (Lepidoptera: Pyralidae). It was determined that: (1) significant interspecific differences occurred between the egg, larval, pupal and total egg-to-adult developmental periods of laboratory raised E. zinckenella and E. hobsoni; (2) the pre-pupal and total egg-to-adult development periods of female E. zinckenella were significantly shorter than for males; (3) the longevity of virgin female E. zinckenella was significantly longer than that of virgin males, or virgin male and female E. hobsoni; (4) interspecific differences occurred in the female: male sex-ratios of laboratory raised adults; (5) peak mating for both species occurred on the second night after eclosion; (6) interspecific differences occurred in the temporal distribution of calling and mating behaviors; (7) repeated mating was observed for both species at a very low frequency; (8) interspecific mating did not occur; (9) female E. zinckenella were significantly more fecund than E. hobsoni; (10) the duration in copulo of E. zinckenella was significantly longer than that of E. hobsoni; and (11) wingtraps baited with virgin females caught only conspecific males, and reduced numbers of males were captured in traps simultaneously baited with virgin females of both species. This study demonstrates distinct biological differences and reproductive isolation between the two Etiella spp.
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  • 5
    ISSN: 1570-7458
    Keywords: calling behaviour ; periodicity ; sex pheromone ; attraction inhibitor ; attraction synergist ; field tests ; Lepidoptera ; Gracillariidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Females of the leaf miner moth Phyllonorycter acerifoliella (Z.) [=Ph. sylvella (Hw.)] and Ph. heegerella (Z.) (Lepidoptera: Gracillariidae: Lithocolletinae) release their sex pheromone at the beginning of photophase. The periodicity of the `calling' behaviour of Ph. acerifoliella females was established. Three compounds from calling virgin Ph. heegerella females were collected by the Solid Phase Micro Extraction (SPME) technique and identified as (Z)-8-tetradecenyl acetate (Z8-14:OAc), tetradecyl acetate (14:OAc) and (Z)-8-tetradecenol (Z8-14:OH) in the ratio (88±3):(2±0.6):(10±5) by capillary gas chromatography and mass spectrometry. Field trapping experiments demonstrated that the first two compounds are important for the attraction of conspecific males. Z8-14:OAc was found to be attractive when tested separately, while 14:OAc acted as synergist. The attractivity of the three component blend was reduced by 10% admixture of either (E)-10-dodecenyl acetate (E10-12:OAc) or (Z)-10-tetradecenyl acetate (Z10-14:OAc). Field tests of Z10-, Z8- and E10-14:OAc, identified from Ph. acerifoliella females, demonstrated that the first two compounds were essential for the attraction of conspecific males; so both are sex pheromone components. The attractivity of the three component blend of Z10- Z8- and E10-14:OAc was reduced by 10% admixture of (E)-10-dodecenol (E10-12:OH). The following four semiochemical compounds, Z8-14:OAc, Z8-14:OH, E10-14:OAc and 14:OAc, identified from phyllonoryctid females, as well as two sex attraction antagonists for Ph. acerifoliella and Ph. heegerella males, E10-12:OAc and Z10-14:OAc, are new for the family Gracillariidae. The results of field trapping experiments revealed mechanisms ensuring the specificity of the chemocommunication systems in Ph. acerifoliella, Ph. heegerella and Ph. ulmifoliella (Hb.) moths.
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  • 6
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    Entomologia experimentalis et applicata 97 (2000), S. 339-346 
    ISSN: 1570-7458
    Keywords: crygenes ; PCR ; Lepidoptera ; Spodoptera ; insecticidal activity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thirty-five strains of the entomopathogenic bacterium Bacillus thuringiensisactive on Spodoptera exigua, were characterized by means of serological identification and determination of crygene contents by PCR. The insecticidal activity of these 35 strains was further confirmed against S. exiguaand tested against two other species of the same genus: S. littoralisand S. frugiperda. The results indicate that serovars aizawai, thuringiensis, and kurstakiwere the most frequent within S. exigua-active strains and that serovar aizawaihad the highest number of strains exhibiting toxicity against the three species bioassayed. The presence in crygenes as determined by PCR suggests a non random distribution of some crygenes among serovars. Genes cry1C, cry1D, and cry1E, which are known to code for proteins toxic against Spodopteraspecies, were very common within S. exigua-active strains, specially in those belonging to serovar aizawai. However, some strains harbouring one or more of these genes were not toxic to S. littoralisor S. frugiperda; and some strains lacking all of the Spodoptera-active genes were found to be toxic to all three species. This suggests differences in the expression levels among strains bearing toxic genes and the involvement of other genes toxic to Spodopteraspecies. Since strains sharing the same crygenes exhibited different host ranges, the results indicate the need to perform toxicity bioassays in addition to other tests (serological identification and PCR) in order to determine the insecticidal activity of B. thuringiensisstrains.
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  • 7
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    Journal of insect behavior 13 (2000), S. 881-900 
    ISSN: 1572-8889
    Keywords: three-dimensional ; flight track recording ; orientation ; pheromones ; plant volatiles ; image analysis ; real time ; Lobesia botrana ; Lepidoptera ; Tortricidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A computer-controlled video system for real-time recording of insect flight in three dimensions is described. The flight paths of moths were recorded in a flight tunnel using two CCD cameras placed adjacent to each other at angles of 45 and 135° to the flight tunnel axis and separated by a distance of 120 cm. They were connected to two 28-level gray-scale frame grabbers via two external synchronizers. The two-dimensional coordinates of the flying insect were obtained from the two cameras at 40-ms intervals and transferred to host computer for processing and monitor for real-time display. Due to speed limitation in the image acquisition hardware, construction of the three-dimensional file was carried off-line. The flying insect was rendered as a dark spot in a bright background using a homogeneous light source. As the insect enters into the field of view of the two cameras, the light distribution changes, and the frame grabber detects only those variation in the light distribution which results from a flying insect. The target insect can be as small as 3 pixels and can be tracked in a stereoscopic field of view 60 cm long and 50 cm high. A method was developed that allowed for scalar scoring of various pheromone sources to assess their attractiveness using vector flight parameters. This method was applied successfully for optimization of pheromone blend of the grapevine moth, Lobesia botrana.
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  • 8
    ISSN: 1572-8781
    Keywords: porous silicon ; cis-platin ; drug delivery ; calcium phosphate ; carbo-platin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Technology
    Notes: Abstract In this work, the incorporation and characterization of cis-platin (cis-diammine dichloroplatinum(II)), carbo-platin [cis-diammine(cyclobutane-1,1-dicarboxylato] platinum(II)), and Pt(en)Cl2 (ethylenediamminedichloro platinum(II)) within layers of calcium phosphate on porous Si/Si substrates are described. These materials have been characterized by scanning electron microscopy, secondary ion mass spectrometry, and X-ray energy dispersive spectroscopy. The diffusion of platinum species from the doped calcium phosphate layers has also been investigated by UV-visible absorption spectrometry and inductively-coupled plasma spectroscopy. The influence of initial platinum concentration, the impact of thermal annealing of the calcium phosphate/porous Si/Si matrix, as well as the effect of varying the ligand coordination sphere of the Pt complex on its ability to be delivered to the surroundings have also been analyzed. For the case of cis-platin, it is found that increasing the concentration of platinum complex in the electrolyte during cathodic growth of calcium phosphate results in a relatively greater concentration of Pt incorporated into the calcium phosphate layers and a larger amount of Pt which subsequently can be delivered to the surrounding medium upon exposure to solvent.
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  • 9
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    Biology and fertility of soils 32 (2000), S. 250-255 
    ISSN: 1432-0789
    Keywords: Key words Acetylene reduction ; Artificial symbiosis ; Cyanobacteria ; Nostoc ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  When wheat (Triticum aestivum L.) seedlings are co-cultivated with Nostoc sp. strain 2S9B in hydroponics, the cyanobacterium colonizes the endorhizosphere at low frequency. Mild sonication of the roots dramatically increased the number of cyanobacteria within the root tissue. The cyanobacteria penetrated the roots in the form of motile filaments (hormogonia), and once inside, they divided and transformed into aseriate packages, which showed nitrogenase activity. Cyanobacteria were found in the intercellular spaces as well as inside the epidermal and cortex cells. By prolonging the sonication time the number of cyanobacterial packages inside the roots increased. However, after reaching a certain abundance the total cyanobacterial biomass within the roots did not change regardless of the sonication time. Besides sonication, other methods of root surface damage also brought about enhanced internal root colonization. Sonication of roots proved to be an efficient way of amplifying the internal root colonization by cyanobacteria and can be suggested as a method for creating a model system in non-legume plant-microbe studies.
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  • 10
    ISSN: 1437-5613
    Keywords: Key words Herbivory ; Plant–herbivore interaction ; Lepidoptera ; Cruciferous plants ; Vegetation texture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Correlation between plant size and reproductive output may be modified by herbivory in accordance with host plant density and the presence of nonhost plants. To elucidate the effects of nonhost plant density and host plant density on the intensity of herbivory and reproductive output of the host plant in relation to plant size under natural conditions, we investigated the abundance of three lepidopteran insects, Plutella maculipennis, Anthocharis scolymus, and Pieris rapae the intensity of herbivory, and fruit set of their host plant, Turritis glabra (Cruciferae). To elucidate the effects of nonhost and host plant density, we selected four categories of plots under natural conditions: low density of nonhost and high density of host plants; low density of both nonhost and host plants; high density of both nonhost and host plants; and high density of nonhost and low density of host plants. The plant size indicated by stem diameter was a good predictor of the abundance of all herbivorous species. The effects of density of nonhost and host plants on the abundance of insects varied among species and stages of insects. As the abundance of insects affected the intensity of herbivory, herbivory was more apparent on larger host plants in plots with low density of both nonhost and host plants. Consequently, the correlation between plant size and the number of fruits disappeared in low plots with density of both nonhost and host plants. In this T. glabra– herbivorous insect system, the density of nonhost plants and host plants plays an important role in modifying the relationship between plants and herbivores under natural conditions.
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  • 11
    ISSN: 1437-5613
    Keywords: Key words Community patterns ; Lepidoptera ; Route order ; Species richness ; Species distribution ; Environmental disturbance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Kitahara and Fujii, in 1994, analyzed the butterfly communities along a gradient of human disturbance by applying the generalist/specialist concept. Butterfly species were classified into generalist or specialist species based on their voltinism (seasonal time dimension) and potential larval resource breadth (food dimension). The community structure and species composition showed the systematic changes along the gradient. To verify the generality of those trends, we monitored five grassland butterfly communities with varying degrees of human disturbance twice a month during 1985 by the line transect method at the foot of Mt. Fuji, central Japan, and analyzed their structure in a manner similar to that employed by Kitahara and Fujii. Most results were consistent with the patterns recognized by Kitahara and Fujii. The route (community) order based on increasing human disturbance was strongly and negatively correlated with butterfly species richness but with neither butterfly species diversity (H′) nor evenness (J′). Also, the degree of human disturbance was significantly and negatively correlated with the number of specialist species, but not with that of generalists, in a community. Butterfly species richness was more strongly correlated with the number of specialist species than with that of generalists. Our analyses also showed that the generalist species were distributed more widely over the communities than were the specialists. However, in contrast to the trend revealed by Kitahara and Fujii, there was no significant difference in the population densities and in the spatial population variability between the two species groups. As a whole, our analyses confirmed the consistency of most community patterns detected by Kitahara and Fujii. The causes of the inconsistencies in some patterns were thought to be mainly the present habitat conditions with a relatively short growing season at high altitudes.
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  • 12
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    Journal of insect conservation 4 (2000), S. 73-77 
    ISSN: 1572-9753
    Keywords: mapping ; database ; bias recording ; Lepidoptera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Nature of Science, Research, Systems of Higher Education, Museum Science
    Notes: Abstract We use data from the Mersey Valley zone (3×2 km area; N = 600 I ha squares) of the Greater Manchester butterfly atlas to investigate whether recorder visits are biased by access (viz. distance from recorder's home base) and by the locations of potential hot spots. In a multiple regression analysis, visits were found to correlate significantly both with distance from home base of the recorder and with the mean and maximum number of species found in squares. Sites close to the home base of the recorder were visited more frequently than those further afield and squares with more species were visited more frequently than those squares with fewer species. Visits were also made significantly more frequently to squares with greater numbers of butterfly resources (e.g. hostplants, nectar). Furthermore, recording is biased to and away from distinct land uses, which vary significantly in species richness. Reasons are given why these biases are to be expected at all scales. The message is that future distribution mapping should be based on rigorous sampling approaches.
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  • 13
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    Oecologia 122 (2000), S. 1-10 
    ISSN: 1432-1939
    Keywords: Key words Distribution ; Gregariousness ; Larval strategy ; Lepidoptera ; Thermoregulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Group-living in animal populations has many possible ecological and evolutionary explanations, including predator evasion and feeding facilitation. In insects, the thermal balance of solitary and gregarious larvae is likely to differ and may thus have important ecological consequences. The abilities of the larvae of four species of nettle-feeding nymphalid butterflies to thermoregulate were quantified in the field. Larval surface body temperatures of the gregarious Aglais urticae (small tortoiseshell) and Inachis io (peacock) and the solitary Polygonia c-album (comma) and Vanessa atalanta (red admiral) were measured for each instar, in both sunny and overcast conditions, over a seasonal range of temperatures. The results suggested two distinct larval thermal strategies. In the presence of direct sunlight, the exposed gregarious larvae of A. urticae and I. io regulated body temperatures at 32.5 and 31.5°C, respectively, while the temperatures of concealed larvae of P. c-album and V. atalanta were largely dependent on ambient temperatures. In the sun, the range of body temperatures recorded for A. urticae and I. io larvae was fairly narrow relative to ambient temperatures. This suggests a high degree of thermal control in these species. Modal body temperatures coincided with the temperature at which development rate is maximal. Regardless of whether changes in thermoregulation are a cause or consequence of the evolution of gregariousness, the combination of behavioural thermoregulation and gregariousness in larval insects has important implications for voltinism patterns and range extension (via increased development rates). Distributional responses of gregarious and solitary larvae to climatic warming may differ as a result of changes in cloud cover as well as changes in temperature.
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  • 14
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    Oecologia 122 (2000), S. 36-43 
    ISSN: 1432-1939
    Keywords: Key words Life history theory ; Longevity ; Ageing ; Mortality rate ; Lepidoptera
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Life history theory predicts that organisms should only invest resources into intrinsic components of life span to the degree that it pays off in terms of reproductive success. Here, we investigate if the temporal distribution of mating opportunities may have influenced the evolution of intrinsic mortality rates in the butterfly Pararge aegeria (Satyrinae). In this species, females mate only once and the frequency of male mating opportunities depends on the temporal emergence pattern of virgin females. As expected, in a population from Madeira where females emerge continuously throughout the year, there was no sex difference in adult life span, while in a Swedish population with synchronised female emergence, males had significantly shorter life spans compared to females. A logistic mortality model provided the best fit to the observed change in age-specific mortality and all categories reached an asymptotic mortality rate of a similar magnitude. However, the Swedish males reached this mortality plateau more rapidly than the other categories. External mortality, due to water and food limitation, affected the pattern of sex-specific mortality but males from Sweden still had higher rates of mortality compared to all other categories. We argue that selection on male longevity is likely to be weaker in Sweden because under synchronised emergence, all females emerge and mate within a short period of time, after which male reproductive value will quickly approach zero. On Madeira, however, male reproductive value decrease more slowly with age since the probability of finding a receptive female is constant over the year.
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  • 15
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    Plant cell reports 19 (2000), S. 1069-1075 
    ISSN: 1432-203X
    Keywords: Key words Green fluorescent protein ; Transformation ; Wheat ; AbbreviationsGFP Green fluorescent protein ; 2,4-D 2,4 Dichorophenoxyacetic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Wheat (Triticum aestivum L.) transformation via particle bombardment is now established in many laboratories, but transformation efficiencies are still largely low and the highest efficiencies can only be obtained with certain genotypes. For rapid optimization and improvement of wheat transformation protocols, a non-destructive marker which permits early detection of transformed cells is needed. We have assessed the ability of a modified version of the Aequorea victoria green fluorescent protein (GFP) to act as a marker for detecting transformed cells and tissues of wheat. Multicellular clusters emitting green fluorescence were observed 14 days after particle bombardment with a sGFPS65T gene construct, and gfp-expressing shoots (often with expressing roots) could be observed as early as 21 days after bombardment. These shoots can be removed from the callus and grown further until they are ready to transfer to soil. Transgenic wheat plants could be selected on the basis of gfp expression alone although the inclusion of antibiotic resistance as a selectable marker could improve the efficiency. Using sgfpS65T as a marker gene in an experiment comparing bombardment parameters allowed the rapid identification of variables that could be targeted for optimization.
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  • 16
    ISSN: 1432-0983
    Keywords: Key words Plant mitochondria ; Heteroplasmy ; NC hybrids ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Mitochondrial (mt) DNA structures were studied in 12 nucleus–cytoplasm (NC) hybrids of tetraploid and hexaploid wheat in which nuclear genomes of the recurrent paternal wheat parents were combined with D and D2 plasmons from Aegilops species. RFLP analysis of 15 mtDNA regions indicated the presence of the paternal sequences in six regions encompassing 11 structural genes in all the NC hybrids. PCR-RFLP analysis showed that one region (a nad3-orf156 region) consisted of a mixture of the maternal, paternal and novel paternal-like sequences. The presence of unexpectedly high levels of the paternal sequences was confirmed by random PCR cloning and sequencing of this region. PCR-RFLP analysis of the random clones further showed that the relative stoichiometry of the maternal and paternal sequences varied depending on the plasmons from the maternal parents and the nuclear backgrounds of the paternal parents. Our results suggest that the differential amplification of the paternal mtDNA sequences is under the control of NC interaction in these NC hybrids.
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  • 17
    ISSN: 1432-2242
    Keywords: Key words Adult-plant disease resistance ; Gene mapping ; Microsatellites ; Puccinia striiformis ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A major gene determining non-specific adult-plant disease resistance against stripe rust (Puccinia striiformis) designated Yrns-B1 was mapped by using a cross between ’Lgst.79–74’ (resistant) and ’Winzi’ (susceptible). Analyzing F3 lines of two consecutive experimental years contrary modes of inheritance were observed due to the intermediate character of the gene and the difference in the disease pressure during the seasons. Using the disease scoring data of both experimental years independently two maps were constructed detecting Yrns-B1 20.5 and 21.7 cM, respectively, proximal to the wheat microsatellite (WMS) marker Xgwm493 on the short arm of chromosome 3BS. The genetic relationships to other major genes or to quantitative trait loci controlling adult plant disease resistance against rusts in wheat are discussed.
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  • 18
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    Theoretical and applied genetics 100 (2000), S. 1100-1107 
    ISSN: 1432-2242
    Keywords: Key words Triticum aestivum L. ; Wheat ; Puroindoline ; Mutations ; Endosperm hardness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Endosperm hardness in wheat (Triticum aestivum L.) is determined by one major genetic factor, the Hardness (Ha) gene on the short arm of chromosome 5D. Grain hardness has previously been reported to result from either a failure to express puroindoline a (Pina–D1b) or a glycine to serine mutation at position 46 in puroindoline b (Pinb–D1b). In this study, which involves a large survey of 343 wheat genotypes of mostly Northern European origin, we report two new mutations in puroindoline b associated with hard endosperm. These were characterized as involving a leucine to proline change at position 60 (Pinb–D1c), and a tryptophan to arginine change at position 44 (Pinb–D1d), respectively. While the former seems to be widely distributed in germplasm around the world, the latter was only found in three winter wheats from Sweden and Netherlands. As discussed in the paper, the three known mutations in puroindoline b can be considered ”loss-of-function” mutations (i.e. soft to hard), and structural analysis may serve to predict that their dramatic effect on wheat grain texture is a result of reduced lipid–binding ability.
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  • 19
    ISSN: 1432-2242
    Keywords: Key words Microsatellite markers ; Wheat ; Genetic diversity ; Genotype identification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A set of 20 wheat microsatellite markers was used with 55 elite wheat genotypes to examine their utility (1) in detecting DNA polymorphism, (2)in the identifying genotypes and (3) in estimating genetic diversity among wheat genotypes. The 55 elite genotypes of wheat used in this study originated in 29 countries representing six continents. A total of 155 alleles were detected at 21 loci using the above microsatellite primer pairs (only 1 primer amplified 2 loci; all other primers amplified 1 locus each). Of the 20 primers amplifying 21 loci, 17 primers and their corresponding 18 loci were assigned to 13 different chromosomes (6 chromosomes of the A genome, 5 chromosomes of the B genome and 2 chromosomes of the D genome). The number of alleles per locus ranged from 1 to 13, with an average of 7.4 alleles per locus. The values of average polymorphic information content (PIC) and the marker index (MI) for these markers were estimated to be 0.71 and 0.70, respectively. The (GT)n microsatellites were found to be the most polymorphic. The genetic similarity (GS) coefficient for all possible 1485 pairs of genotypes ranged from 0.05 to 0.88 with an average of 0.23. The dendrogram, prepared on the basis of similarity matrix using the UPGMA algorithm, delineated the above genotypes into two major clusters (I and II), each with two subclusters (Ia, Ib and IIa, IIb). One of these subclusters (Ib) consisted of a solitary genotype (E3111) from Portugal, so that it was unique and diverse with respect to all other genotypes belonging to cluster I and placed in subcluster Ia. Using a set of only 12 primer pairs, we were able to distinguish a maximum of 48 of the above 55 wheat genotypes. The results demonstrate the utility of microsatellite markers for detecting polymorphism leading to genotype identification and for estimating genetic diversity.
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  • 20
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    Theoretical and applied genetics 100 (2000), S. 271-279 
    ISSN: 1432-2242
    Keywords: Key words Spelt ; Wheat ; γ-Gliadins ; PCR ; Molecular markers
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Polymerase chain reaction (PCR) primers GAG5 and GAG6 were designed based on published γ-gliadin gene sequences and applied to 35 cultivars of closely related spelt (Triticum spelta L.) and hexaploid wheat (T. aestivum L.). Eight tetraploid durum wheat (T. durum Desf.) cultivars were included in the analysis. The obtained PCR products originated from two γ-gliadin genes which were mapped to homeologous chromosomes 1B and 1D and termed GAG56B and GAG56D, respectively. Two alleles of GAG56D differing in a 9-bp deletion/duplication and single nucleotide polymorphism were found. The 18 spelts tested and wheat cultivar ’Chinese Spring’ were discovered to carry a previously unknown γ-gliadin gene, while 16 wheat cultivars possessed its longer, already published allele. Two PCR-based detection systems for the diagnostic alleles were developed and applied. The occurrence of two alleles of GAG56B among the investigated durum wheats correlated with their expression of gluten quality markers γ-gliadins 42 or 45.
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  • 21
    ISSN: 1432-2242
    Keywords: Key words Boron toxicity ; Boron tolerance ; Mapping ; Wheat ; Marker-assisted selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Boron is an essential plant micro-nutrient which can be phytotoxic to plants if present in soils in high concentration. Boron toxicity has been recognised as an important problem limiting production in the low rainfall areas of southern Australia, West Asia and North Africa. Genetic variation for boron toxicity tolerance in wheat has been well-characterised. The efficiency of breeding for boron toxicity tolerance could be greatly enhanced by the development of molecular markers associated with QTLs for tolerance in wheat. A population of 161 doubled haploids from a cross between the tolerant cultivar Halberd and the moderately sensitive cultivar Cranbrook was used to identify chromosomal regions involved in boron tolerance. A combined RFLP and AFLP linkage map of the Cranbrook x Halberd population was used to identify chromosomal regions involved in the boron tolerance traits measured. Regions on chromosome 7B and 7D were associated with leaf symptom expression. The region on chromosome 7B was also associated with the control of boron uptake and with a reduction in the effect of boron toxicity on root-growth suppression. RFLP markers at the chromosome 7B and 7D loci were shown to be effective in selecting for improved boron tolerance in an alternative genetic background. Halberd alleles at the chromosome 7B locus were associated with the concentration of boron in whole shoots and grain. The concentration of boron in whole shoots and in grain were both related to grain yield in a field trial conducted on soil containing toxic levels of boron. Implications relating to marker-assisted selection for boron toxicity tolerance in wheat are discussed.
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  • 22
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    Theoretical and applied genetics 100 (2000), S. 494-497 
    ISSN: 1432-2242
    Keywords: Key words Ex-situ conservation ; Genebank collection ; Long term storage ; Mikrosatellites ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The genetic identity of eight wheat (Triticum aestivum L.) accessions maintained in the Gatersleben genebank and regenerated up to 24 times was studied by using wheat microsatellite markers (WMS). It was demonstrated that WMS can be used to analyze bulks of seeds stored more than 50 years in a seed reference collection at room temperature. No contamination due to foreign pollen or incorrect handling during the multiplication cycles was discovered. For one accession (TRI 4599) genetic drift was observed, whereas for TRI 249 a heterogenous situation for two markers was maintained over the years. We were able to show that microsatellites can be used as a simple and reliable marker system for the verification of the integrity and genetic stability of genebank accessions.
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  • 23
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    Theoretical and applied genetics 100 (2000), S. 545-551 
    ISSN: 1432-2242
    Keywords: Key words Automated genotyping ; Fluorescence-based DNA analysis ; AFLP ; Barley ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Genetic mapping and the selection of closely linked molecular markers for important agronomic traits require efficient, large-scale genotyping methods. A semi-automated multifluorophore technique was applied for genotyping AFLP marker loci in barley and wheat. In comparison to conventional 33P-based AFLP analysis the technique showed a higher resolution of amplicons, thus increasing the number of distinguishable fragments. Automated sizing of the same fragment in different lanes or different gels showed high conformity, allowing subsequent unambigous allele-typing. Simultaneous electrophoresis of different AFLP samples in one lane (multimixing), as well as simultaneous amplification of AFLP fragments with different primer combinations in one reaction (multiplexing), displayed consistent results with respect to fragment number, polymorphic peaks and correct size-calling. The accuracy of semi-automated co-dominant analysis for hemizygous AFLP markers in an F2 population was too low, proposing the use of dominant allele-typing defaults. Nevertheless, the efficiency of genetic mapping, especially of complex plant genomes, will be accelerated by combining the presented genotyping procedures.
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  • 24
    ISSN: 1573-4919
    Keywords: endosulfan ; cytotoxicity ; mitochondria ; apoptosis ; Jurkat cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Several organochlorinated pesticides including DDT, PCBs and dieldrin have been reported to cause immune suppression and increase susceptibility to infection in animals. Often this manifestation is accompanied by atrophy of major lymphoid organs. It has been suggested that increased apoptotic cell death leading to altered T-B cell ratios, and loss of regulatory cells in critical numbers leads to perturbations in immune function. The major objective of our study was to define the mechanism by which endosulfan, an organochlorinated pesticide, induces human T-cell death using Jurkat, a human T-cell leukemic cell line, as an in vitro model. We exposed Jurkat cells to varying concentrations of endosulfan for 0-48 h and analyzed biochemical and molecular features characteristic of T-cell apoptosis. Endosulfan lowered cell viability and inhibited cell growth in a dose- and time-dependent manner. DAPI staining was used to enumerate apoptotic cells and we observed that endosulfan at 10-200 μM induced a significant percentage of cells to undergo apoptotic cell death. At 48 h, more than 90% cells were apoptotic with 50 μM of endosulfan. We confirmed these observations using both DNA fragmentation and annexin-V binding assays. It is now widely being accepted that mitochondria undergo major changes early during the apoptotic process. We examined mitochondrial transmembrane potential (ΔΨm) in endosulfan treated cells to understand the role of the mitochondria in T-cell apoptosis. Within 30 min of chemical exposure, a significant percentage of cells exhibited a decreased incorporation of DiOC6(3), a cationic lipophilic dye into mitochondria indicating the disruption of ΔΨm. This drop in ΔΨm was both dose- and time-dependent and correlated well with other parameters of apoptosis. We also examined whether this occurred by the down regulation of bcl-2 protein expression that is likely to increase the susceptibility of Jurkat cells to endosulfan toxicity. Paradoxically, the intracellular expression of bcl-2 protein was elevated in a dose dependent manner suggesting endosulfan-induced apoptosis occurred by a non-bcl-2 pathway. Based on these data, as well as those reported elsewhere, we propose the following sequence of events to account for T-cell apoptosis induced by endosulfan: uncoupling of oxidative phosphorylation → excess ROS production → GSH depletion → oxidative stress → disruption of ΔΨm → release of cytochrome C and other apoptosis related proteins to cytosol → apoptosis. This study reports for the first time that endosulfan can induce apoptosis in a human T-cell leukemic cell line which may have direct relevance to loss of T cells and thymocytes in vivo. Furthermore, our data strongly support a role of mitochondrial dysfunction and oxidative stress in endosulfan toxicity.
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  • 25
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    Molecular and cellular biochemistry 204 (2000), S. 83-88 
    ISSN: 1573-4919
    Keywords: FHIT ; cell cycle ; ecdysone ; tumor suppressor ; apoptosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The mechanism of tumor suppressor action of the fragile histidine triad (FHIT) gene is unknown. Disruption of cell cycle regulation leads to the tumor formation and many tumor suppressor genes suppress tumorigenesis through their effect on cell cycle regulation. We examined the expression of FHIT during the cell cycle, and determined whether overexpression of FHIT affects cell cycle kinetics and apoptosis. The FHIT cDNA was cloned into the ecdysone-inducible expression vector in both the sense and antisense orientations. Overexpression of the sense or antisense construct did not affect cell proliferation, cell cycle distribution or apoptosis in human 293T cells. Analysis of the FHIT expression in 293T cells collected at various cell cycle phases showed that the expression of FHIT is not under cell cycle regulation. These results indicate that the tumor suppressor activity of the FHIT gene may be independent of an effect on the cell cycle and apoptosis mechanisms.
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  • 26
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    Molecular and cellular biochemistry 212 (2000), S. 19-28 
    ISSN: 1573-4919
    Keywords: melanoma ; transcription factors ; CREB ; invasion ; apoptosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The purpose of this study was to determine the role of CREB and its associated proteins in melanoma progression. We used MeWo human melanoma cells transfected with a dominant negative construct of CREB, KCREB. KCREB has a mutation in its DNA-binding domain and can not bind the CRE element. Expression of KCREB yields proper heterodimerization with CREB and its associated proteins, but the proteins associated with KCREB do not confer the same degree of transcriptional activity as they would in the case of wild-type CREB. Here, we demonstrate that expression of KCREB in MeWo melanoma cells leads to a decrease in their tumorigenicity and metastatic potential in nude mice. We identified two mechanisms that explain at least partially this effect of KCREB. The first, is one in which CREB and its associated proteins play an essential role in invasion. We showed that the invasive properties of KCREB-transfected MeWo cells were reduced due to the downregulation of the CRE-dependent expression of the type IV collagenase MMP-2 and the adhesion molecule MCAM/MUC18. In the second mechanism, CREB and its associated proteins act as survival factors for human melanoma cells. Here we demonstrated that expression of KCREB in MeWo cells rendered them susceptible to apoptosis induced by thapsigargin, which in turn increased the intracellular level of Ca2+. Thapsigargin induced CREB and ATF-1 phosphorylation and activated CRE-dependent transcription in MeWo cells. Collectively, our data demonstrate that CREB and its associated proteins play an important role in tumor growth and metastasis of human melanoma.
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  • 27
    ISSN: 1573-4919
    Keywords: T-type Ca2+ channel ; polyglutamine-expanded androgen receptor ; CAG trinucleotide repeats ; spinobulbar muscular atrophy ; apoptosis ; motorneuron ; cell lines ; neuroblastoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract We have analyzed Ca2+ currents in two neuroblastoma-motor neuron hybrid cell lines that expressed normal or glutamine-expanded human androgen receptors (polyGln-expanded AR) either transiently or stably. The cell lines express a unique, low-threshold, transient type of Ca2+ current that is not affected by L-type Ca2+ channel blocker (PN 200-110), N-type Ca2+ channel blocker (ω-conotoxin GVIA) or P-type Ca2+ channel blocker (Agatoxin IVA) but is blocked by either Cd2+ or Ni2+. This pharmacological profile most closely resembles that of T-type Ca2+ channels [1-3]. Exposure to androgen had no effect on control cell lines or cells transfected with normal AR but significantly changed the steady-state activation in cells transfected with expanded AR. The observed negative shift in steady-state activation results in a large increase in the T-type Ca2+ channel window current. We suggest that Ca2+ overload due to abnormal voltage-dependence of transient Ca2+ channel activation may contribute to motor neuron toxicity in spinobulbar muscular atrophy (SBMA). This hypothesis is supported by the additional finding that, at concentrations that selectively block T-type Ca2+ channel currents, Ni2+ significantly reduced cell death in cell lines transfected with polyGln-expanded AR.
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  • 28
    ISSN: 1573-4919
    Keywords: retinoic acid ; RARβ ; protein kinase A ; apoptosis ; caspase
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    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Both cAMP and retinoids play a role in cell differentiation and the control of cell growth. A site-selective cAMP analog, 8-Cl-cAMP and retinoic acid synergistically inhibit growth and induce apoptosis in certain cancer cells. In advanced or recurrent malignant diseases, retinoic acid (RA) is not effective even at doses that are toxic to the host. The objective of our present study was to examine the mechanism(s) of synergistic effects of retinoic acid (9-cis, 13-cis or all-trans RA) and 8-Cl-cAMP on apoptosis in human ovarian cancer NIH: OVCAR-3 and OVCAR-8 cells. RA induced growth inhibition and apoptosis in OVCAR-3 and OVCAR-8 cells. 8-Cl-cAMP acted synergistically with RA in inducing and activating retinoic acid receptor β (RARβ) which correlates with growth inhibition and apoptosis in both cell types. In addition, induction of apoptosis by RA plus 8-Cl-cAMP requires caspase-3 activation followed by cleavage of anti-poly(ADP-ribose) polymerase. Furthermore, mutations in CRE-related motif within the RARβ promoter resulted in loss of both transcriptional activation of RARβ and synergy between RA and 8-Cl-cAMP. RARβ expression appears to be associated with induction of apoptosis. Introduction of the RARβ gene into OVCAR-3 cells resulted in gain of RA sensitivity. Loss of RARβ expression, therefore, may contribute to the tumorigenicity of human ovarian cancer cells. Thus, combined treatment with RA and 8-Cl-cAMP may provide an effective means for inducing RARβ expression leading to apoptosis in ovarian cancer cells.
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  • 29
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    Molecular and cellular biochemistry 203 (2000), S. 59-71 
    ISSN: 1573-4919
    Keywords: PTEN tumor suppressor ; cyclin-dependent kinase inhibitors ; apoptosis ; chemosensitivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The recently discovered tumor suppressor gene PTEN has been found mutated in many types of advanced tumors. When introduced into tumor cells that lack the wild-type allele of the gene, PTEN was able to suppress the growth of these cells. Here, we have analyzed how PTEN might alter cell cycle-regulatory controls to achieve this growth-inhibitory effect. We found that overexpression of PTEN stimulates the synthesis of three inhibitors of cyclin-dependent kinases, p21WAF1, p27KIP1, and p57,KIP2. This effect is very specific, as the expression of other components of the cell cycle engine, various cyclins and cyclin-dependent kinases, is not affected. For p21WAF1 we show that this induction is due to the p53-independent transcriptional activation of its promoter. In addition, increased expression of PTEN rendered the cells more sensitive to apoptotic cell death. Therefore, our data suggest a two-fold mechanism of growth inhibition by PTEN: one that acts via the increased expression of CKIs such as p21WAF1, and another that augments the cellular propensity for apoptotic cell death.
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  • 30
    ISSN: 1573-4919
    Keywords: tumour necrosis factor ; receptors ; subtypes ; calcium ; apoptosis ; cancer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Tumour necrosis factor-α (TNF) receptors mediate a variety of effects dependent on cell type. A role for Ca2+ in TNF-induced death remains uncertain. Here we investigated restricting intracellular/extracellular Ca2+ in HeLa epithelial carcinoma cells expressing low and high levels of p75TNFR receptor subtype and KYM-1 rhabdomyosarcoma cells, models of rapid TNF-induced apoptosis. Ca2+-chelators EGTA and BAPTA-AM as well as microsomal Ca2+-ATPase inhibitor thapsigargin, did not alter TNF-induced death. TNF was also unable to alter resting [Ca2+]i levels which remained 〈 200 nM even during times when these cells were undergoing apoptotic cell death. These findings indicate no role for modulated Ca2+ concentrations in TNF-induced apoptotic cell death.
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  • 31
    ISSN: 1573-1561
    Keywords: Insect pheromones ; pheromone emission ; aggressive chemical mimicry ; predation ; allomone ; Araneae ; Araneidae ; Lepidoptera ; Noctuidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The adult female bolas spider Mastophora hutchinsoni feeds exclusively on attracted males of a few moth species. This exclusivity and the behavior of the approaching moths suggest that the spider aggressively mimics the sex pheromones of its prey species. Males of the bristly cutworm, Lacinipolia renigera, are a major prey of this spider, accounting for about two thirds of the biomass of prey consumed. Female bristly cutworms produce a pheromone blend consisting of (Z)-9-tetradecenyl acetate (Z9–14 : Ac) and (Z,E)-9,12-tetradecenyl acetate (ZE-9,12–14 : Ac). To determine if M. hutchinsoni females mimic the sex pheromone components and blend ratio of L. renigera, we collected volatiles from hunting adult female spiders and analyzed them with gas chromatography–electroantennographic detection (GC-EAD) and gas chromatography–mass spectrometry (GC-MS). GC-EAD analysis of volatile collections, using a male bristly cutworm antenna as the detector and two capillary columns of different polarities, revealed the presence of peaks with retention times (R ts) identical to Z9–14 : Ac and ZE-9,12– 14 : Ac. The mass spectrum of a peak with R t of Z9–14 : Ac was identical to the mass spectrum of the synthetic equivalent. There was an insufficient quantity of the compound with R t of ZE-9,12–14 : Ac to get a full spectrum, but selective detection of ions at m/z 61 and 192 at the correct R t supported the identification. On average, the blend collected from spiders contained 54.8 ± 20.8 (SE) pg/min of Z9–14 : Ac and 2.5 ± 1.7 (SE) pg/min of ZE-9,12–14 : Ac. The latter, on average, comprised 2.6 ± 0.7% of the total, which is similar to the blend ratio emitted by bristly cutworm females. Our results indicate that the adult female M. hutchinsoni produces an allomone blend that mimics not only the composition, but also the blend ratio, of the sex pheromone of a major prey species.
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  • 32
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    Journal of chemical ecology 26 (2000), S. 1983-1990 
    ISSN: 1573-1561
    Keywords: Setora nitens ; Setothosea asigna ; nettle caterpillar ; Limacodidae ; Lepidoptera ; sex pheromone ; (Z)-9-dodecenal ; (Z)-9,11-dodecadienal ; (E)-9-dodecenal ; (E)-9,11-dodecadienal ; oil palm ; Elaeis guineensis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Gas chromatographic–electroantennographic detection (GC-EAD) analyses of pheromone gland extracts of female nettle caterpillars, Setora nitens, revealed four compounds that consistently elicited responses from male moth antennae. Retention indices on three fused silia columns (DB-5, DB-23, and DB-210) of two EAD-active compounds were almost identical to those of (E)-9-dodecenal (E9–12 : Ald) and (E)-9,11-dodecadienal (E9,11–12 : Ald), two pheromone components previously identified in congeneric Setothosea asigna. However, comparative GC, GC-EAD, and GC-mass spectrometry of extracted S. nitens compounds and authentic standards revealed that the candidate pheromone components were (Z)-9-dodecenal (Z9–12 : Ald) and (Z)-9,11-dodecadienal (Z9,11–12 : Ald). The two other EAD-active compounds in pheromone gland extracts proved to be the corresponding alcohols to these aldehydes. In field-trapping experiments in Tawau, Malaysia, synthetic Z9–12 : Ald and Z9,11–12 : Ald at a 1 : 1 ratio, but not singly, attracted male S. nitens. Attractiveness of these two aldehydes could not be enhanced through the addition of their corresponding alcohols. Whether these differences in pheromone biology and chemistry between S. nitens and S. asigna are sufficient to prevent cross-attraction of heterospecific males or whether nonpheromonal mechanisms are required to maintain reproductive isolation is currently being studied.
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  • 33
    ISSN: 1573-4919
    Keywords: etoposide ; Bcl-XL ; Bax ; apoptosis ; K562 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Etoposide is a potent anticancer agent that is used to treat various tumors. We have investigated the dose-dependent effect of etoposide on apoptosis using chronic myeloid leukemia K562 cells treated with low (5 μM) or high (100 μM) concentrations of the drug. At a low concentration, etoposide induced little apoptosis at 24 h, while about 20% of the cells showed apoptosis morphologically at a high concentration. Processing of caspase-3 was slightly detected from 12 h and became obvious at 24 h with 100 μM etoposide. Caspase-3-like protease activity was detected at 24 h with a high concentration. Moreover, these changes were accompanied by cleavage of poly ADP ribose polymerase (PARP). Changes of the mRNA levels of most apoptosis-regulating genes were not prominent at both concentrations, except for the rapid induction of c-IAP-2/HIAP-1 and the down-regulation of Bcl-XL by 100 μM etoposide. The downregulation of Bcl-XL protein occurred from 6 h, while Bax protein conversely showed a slight increase from 6 h. Taken together, the present findings show that the dose-dependent apoptotic effect of etoposide is based on a change in the balance between Bcl-XL and Bax, which precedes the activation of caspase-3.
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  • 34
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    Molecular and cellular biochemistry 207 (2000), S. 19-27 
    ISSN: 1573-4919
    Keywords: PKC ; apoptosis ; bile acid ; hepatocyte
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The effect of GCDC-induced apoptosis on PKC activity and PKC's role in GCDC-induced hepatocyte apoptosis is unclear. The specific aims of this study were to determine if GCDC-induced apoptosis changed intracellular PKC activity and if modulation of PKC activity affected GCDC-induced hepatocyte apoptosis. Apoptosis was induced in isolated hepatocytes using GCDC. PKC activity was measured and specific PKC and calpain inhibitors were used to study the effects of PKC and calpain modulation on GCDC-induced apoptosis. After 4 h exposure, 50 μM GCDC induced apoptosis in 42% of hepatocytes. Intracellular PKC activity decreased to 44% of controls 2 h after exposure of hepatocytes to GCDC (p 〈 0.001). Pre-incubation of hepatocytes with the calpain protease inhibitor restored PKC activity in GCDC exposed hepatocytes to 91± 5% of control cells. Pre-incubation of hepatocytes with a calpain inhibitor decreased GCDC-induced apoptosis as did pre-incubation with the PKC activating phorbol ester, PMA. The combination of calpain inhibition and PMA further reduced GCDC-induced apoptosis but caused low level hepatic apoptosis. Inhibition of PKC with chelerythrine also substantially reduced GCDC-induced hepatocyte apoptosis. GCDC-induced apoptosis is associated with decreases in total cellular PKC activity, which appear to be dependent on intracellular calpain-like protease activity. The combination of protease inhibition and phorbol ester pretreatment preserved total cellular PKC activity and decreased GCDC-induced apoptosis but induced low level apoptosis in the absence of GCDC exposure. PKC inhibition also decreased GCDC-induced hepatocyte apoptosis highlighting the complex interactions of PKC and proteases during GCDC-induced apoptosis.
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  • 35
    ISSN: 1573-4919
    Keywords: phosphatidylserine ; base exchange ; apoptosis ; thymocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The exposure of phosphatidylserine toward the external surface of the membrane is a well-established event of programmed cell death. The possibility that an apoptotic stimulus influences the metabolism of this phospholipid could be relevant not only in relation to the previously mentioned event but also in relation to the capability of membrane phosphatidylserine to influence PKC activity. The present investigation demonstrates that treatment of mouse thymocytes with the apoptotic stimulus dexamethasone, enhances the incorporation of [3H]serine into phosphatidylserine. Cell treatment with dexamethasone also enhanced the activity of serine base exchange enzyme, assayed in thymocyte lysate. Both the effects were observed at periods of treatment preceding DNA fragmentation. The addition of unlabelled ethanolamine, together with [3H]serine to the medium containing dexamethasone-treated thymocytes lowered the radioactivity into phosphatidylserine. Serine base exchange enzyme activity was influenced by the procedure used to prepare thymocyte lysate and was lowered by the addition of fluoroaluminate, that is widely used as a G-protein activator. The increase of serine base exchange enzyme activity induced by dexamethasone treatment was observed independently by the procedure used to prepare cell lysate and by the presence or absence of fluoroaluminate.
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  • 36
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    Molecular and cellular biochemistry 212 (2000), S. 35-43 
    ISSN: 1573-4919
    Keywords: cAMP ; CRE ; Cox-2 ; NO ; apoptosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Previous studies revealed that expression and activation of cyclooxygenase-2 (Cox-2) conveyed a protective principle in murine macrophages, thus attenuating pro-apoptotic actions of chemotherapeutic agents or programmed cell death as a result of massive nitric oxide (NO) generation. Expression of Cox-2 was achieved by treatment of cells with lipopolysaccharide/interferon-γ or nontoxic doses of NO releasing agents. We reasoned E-type prostanoid formation, and in turn an intracellular cAMP increase as the underlying protective mechanism. To prove our hypothesis, we analyzed the effects of lipophilic cAMP-analogs on NO, cisplatin, or etoposide induced apoptosis in RAW 264.7 macrophages. Selected apoptotic parameters comprised DNA fragmentation (diphenylamine assay), annexin V staining of phosphatidylserine, caspase activity (quantitated by the cleavage of a fluorogenic caspase-3-like substrate Ac-DEVD-AMC), and mitochondrial membrane depolarisation (ΔΨ). Western blots detected accumulation of the tumor suppressor protein p53, relocation of cytochrome c to the cytosol, and expression of the anti-apoptotic protein Bcl-xL. Prestimulation with lipophilic cAMP-analogs attenuated apoptosis with the notion that cell death parameters were basically absent. To verify gene induction by cAMP in association with protection we established activation of cAMP response element binding protein (CREB) by gel-shift analysis and moreover, treated macrophages with oligonucleotides containing a cAMP-responsive element (CRE) in order to scavenge CREB. Decoy oligonucleotides, but not control oligonucleotides, attenuated cAMP-evoked protection and reestablished pro-apoptotic parameters. We conclude that gene induction by cAMP protects macrophages towards apoptosis that occurs as a result of excessive NO formation or addition of chemotherapeutica. Attenuating programmed cell death by the cAMP-signaling system may be found in association with Cox-2 expression and tumor formation.
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  • 37
    ISSN: 1573-4978
    Keywords: apoptosis ; CD95 ; human hepatoma cell ; hydrogen peroxide ; p53
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Reactive oxygen species (ROS) play an important role in cell death induced by many different stimuli. Direct exposure of human hepatoma cell line SMMC-7221 to hydrogen peroxide (H2O2) can induce apoptosis characterized by morphological evidence and fragmentation of DNA assayed by terminal deoxynucleotidyl transferase assay (TUNEL assay). Analysis of flow cytometry indicated that H2O2 can decrease the level of CD95(APO-1/Fas), and it is confirmed that H2O2 can also activate the differential expression of some specific gene such as p53 by means of RT-PCR technique. The results indicated that CD95 signal transduction system may be involved in the H2O2-induced apoptosis, and can regulate some specific genes associated with apoptosis in transcription and translation levels such as p53.
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  • 38
    ISSN: 1432-203X
    Keywords: Key words bar ; Embryos ; Microprojectile ; Transgene ; Wheat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  A method for producing large numbers of transgenic wheat plants has been developed. With this approach, an average of 9.7% of immature embryo explants were transformed and generated multiple self-fertile, independently transformed plants. No untransformed plants, or escapes, were regenerated. This transformation procedure uses morphogenic calli derived from scutellum tissue of immature embryos of Triticum aestivum cv. Bobwhite co-bombarded with separate plasmids carrying a selectable marker gene (bar) and a gene of interest, respectively. Transformed wheat calli with a vigorous growth phenotype were obtained by extended culture on media containing 5.0 mg/l bialaphos. These calli retained morphogenic potential and were competent for plant regeneration for as long as 11 months. The bar gene and the gene of interest were co-expressed in T0 progeny plants. This wheat transformation protocol may facilitate quantitative production of multiple transgenic plants and significantly reduce the cost and labor otherwise required for screening out untransformed escapes.
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  • 39
    ISSN: 1432-0762
    Keywords: Key words Copulation duration ; Explosive mating system ; Ejaculate size ; Lepidoptera ; Mating history
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    Topics: Biology
    Notes: Abstract  The mating system of the Australian lycaenid butterfly, Jalmenus evagoras, is highly unusual compared to most other Lepidoptera. Characteristics of this system, which has been termed an ’explosive mating strategy,’ include the formation of an intensely competitive mating aggregation of males, a highly male biased operational sex ratio, a lack of discrimination and mate choice by both sexes, a high variance in male mating success, and female monogamy. In this study, we tested the hypothesis that multiple mating by males imposes physiological costs resulting in smaller spermatophores, and that this results in a fitness cost to females. We found that male J. evagoras transferred only 2.2% of their eclosion weight during their first mating, consistent with the hypothesis that males of monandrous species produce a relatively small investment. The wet weight of the ejaculate declined by an average of 27% at the second mating and the dry weight by 29%, and an intermating interval of 5–9 days was needed for the ejaculate to return to the size at the first mating, regardless of male size or age. Wet ejaculate mass increased proportionally with male size, though dry mass was proportionally larger in smaller males. Ejaculate mass tended to increase with male age at both first and second matings. Female characteristics, in general, did not affect ejaculate mass, although the wet weight of the ejaculate was positively associated with female weight at the second mating. Copulation duration increased from 2.4 h to approximately 3 h at the second mating, and to over 4 h at the third and fourth matings. Fecundity was positively correlated with female size but not with mating history, copulation duration, or any other characteristics measured for either males or females. Female longevity declined significantly as the number of times the male partner had previously mated increased. We conclude that despite the small male investment in ejaculate, the costs of multiple mating may nonetheless be significant, as indicated by the reduction in ejaculate mass, an increase in copulation duration, and reduction in female lifespan with increasing mating number.
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    Molecular biology 34 (2000), S. 875-887 
    ISSN: 1608-3245
    Keywords: antisense oligonucleotides ; oncogenesis ; therapy of cancer ; apoptosis ; bcl family
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    Topics: Biology
    Notes: Abstract Members of the bcl-2 family genes are thought to be central regulators of apoptosis. Overexpression of antiapoptotic proteins, such as Bcl-2 and Bcl-xL, contributes not only to the development of cancer but also to its resistance against a wide variety of anticancer agents. Thus, downregulation of Bcl-2 and Bcl-xL can potentially be used to improve therapeutic approaches to advanced cancer. The use of antisense biotechnology to downregulate antiapoptotic bcl family members in diverse cancers in vitro and in vivo is reviewed. The effects and potential limitations of antisense strategies are also discussed in the context of a critical view of recent research in the field.
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  • 41
    ISSN: 1618-2545
    Keywords: apoptosis ; caspase-3 ; E2F factor ; Lentinula edodes ; mycelial culture broth
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    Topics: Biology
    Notes: Abstract Extracts fromshiitake (Lentinula edodes) mycelial culture broth, by an organic solvent ethyl acetate, inhibited the proliferation of cultured cells. At lower concentrations (1.25–15 μg/ml), this inhibition, measured by the MTT assay, was dose- and cell line-dependent. Inhibition of tumor cells, such as Caski, SiHa, HeLa, HP-1 and A375, byL. edodes-436 extracts was stronger than inhibition of normal cells (3T3). At 20 μg/ml, the extracts induced changes in cell shape, DNA-fragmentation and the activation of caspase-3. The extracts also inhibited the binding of E2F protein to its promoter. The results suggest that extracts ofL. edodes culture broth contain substances that have the ability to induce apoptosis in the cultured cells.
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  • 42
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    Protoplasma 211 (2000), S. 94-102 
    ISSN: 1615-6102
    Keywords: Androgenesis ; Embryogenesis ; Microspore culture ; Pollen ; Ultrastructure ; Wheat
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    Topics: Biology
    Notes: Summary We have made a detailed cytological examination of the development of wheat embryoids, monitoring their initial divisions from two to ten cells by both light and electron microscopy. According to our observations the first embryogenic division is symmetrical. After the androgenesis induction treatment, there is a decrease in ribosome population with cells that have inactive nucleoli made up almost exclusively of a dense fibrillar component. This population is restored after initial embryogenic divisions. During the initial divisions the embryogenic pollen grains do not appear to change in size and the pollen wall remains intact. The exine undergoes no modification but the intine thickens, and we have observed that the thickness of the intine can be used as a cytological marker of androgenesis. The walls separating the cells obtained after embryogenic division contained numerous plasmodesmata. The beginnings of embryo polarization and cell differentiation could be made out in the very early pollen embryoids.
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  • 43
    ISSN: 1615-6110
    Keywords: Angiosperms ; Campanulaceae ; Wahlenbergia ; Breeding system ; pollination ; pollen collecting hairs ; autogamy ; self-compatibility ; nectar ; island biology ; Juan Fernández Islands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The reproductive biology ofW. berteroi, W. fernandeziana, and a putative hybrid betweenW. fernandeziana andW. grahamiae, endemic to Robinson Crusoe Island (Juan Fernández archipelago, Chile) was studied. Flowers are hermaphroditic, protandrous, offer nectar, and exhibit secondary pollen presentation involving pollen collecting hairs on the style. These features imply allogamy and biotic pollination. However, male and female phases overlap and no effective pollinators were observed. Experimental data indicate these taxa are self-compatible and facultatively autogamous, a conclusion also suggested by the pollen/ovule ratios. Selfing is accomplished when the stigmatic lobes reflex and touch the style, except forW. berteroi where they do not reflex completely. Autogamy is accomplished in the latter when pollen grains deposited on the inner surface of the corolla throat by the “pollen brush” are gathered by stigmatic lobes when shaken by wind. The degree of autogamy, and perhaps self-compatibility, seems to be inconstant, as implied by the variable natural seed set (overall range 21–188 seeds per fruit). A mixed mating system — primarily outcrossing/entomophilous, but also autogamous — must have been present in the continental ancestors of these taxa. Autogamy promoting self-fertilization is important now — on an island with scarce pollinators — and in the past — when the first founders arrived.
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  • 44
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    Journal of porous materials 7 (2000), S. 295-298 
    ISSN: 1573-4854
    Keywords: porous silicon ; photo-voltage ; d.c. conductivity
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this study n-type and p-type PV devices have been fabricated by anodising Si wafers with various resistivities in aqueous ethanoic HF solution followed by deposition of semitransparent contacts. semitransparent deposition onto the porous layers. Various methods have been used for the optimisation of problematic contact to nanoporous layers. The measurements of importance are current-voltage (I-V) characteristics, the photovoltaic (PV) decay time spectrum, and the PV response as a function of excitation energy.
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  • 45
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    Journal of porous materials 7 (2000), S. 307-310 
    ISSN: 1573-4854
    Keywords: porous silicon ; photoluminescence ; degradation
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The evolution, under vacuum, of the photoluminescence (PL) intensity of porous silicon (PS) has been studied as function of anodisation conditions, laser line and post-anodisation treatments. It was shown that the degradation of the PL intensity depends on the internal structure of PS. In particular, the degradation is important for PS layers formed essentially by crystallites having small size or where amorphous phase exists. The experimental results have been interpreted using a theoretical model, which takes into account the variation with time of the local concentration of the luminescent centers.
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  • 46
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    Journal of porous materials 7 (2000), S. 319-321 
    ISSN: 1573-4854
    Keywords: porous silicon ; stress measurements ; thermal annealing
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Macroscopic stress measurements are used to monitor Porous Silicon processing. Silicon wafer of 1Ω cm resistivity, n-type and 〈1 0 0〉 orientation were used as starting material. Porous Silicon layers with a porosity of 57% and a thickness of 85 μm, fabricated by electrochemical anodisation, were differently dried, then the evolution of the wafer deflection has been followed with storage time in air. Thermal treatments both in inert and oxidant atmosphere have been performed up to 1000°C. The stress behaviour vs. temperature allows to estimate the hydrogen desorption activation energy.
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  • 47
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    Journal of porous materials 7 (2000), S. 373-376 
    ISSN: 1573-4854
    Keywords: porous silicon ; superlattices ; oxidation
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Initial stage of porous silicon (PS) formation has been studied in an original way. Multilayer structures constituting of very thin layers of low porosity and thick layers of high porosity have been fabricated and characterised by optical tools and electron microscopy. The non linear behaviour resulting in a change in the dissolution velocity has been quantified by using a stack layer structure. Finally using thermal oxidation it has been shown that, due to the selective oxidation as a function of the porosity, porous silicon can be used to produce a Si/SiO2 like structure.
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  • 48
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    Journal of porous materials 7 (2000), S. 345-348 
    ISSN: 1573-4854
    Keywords: porous silicon ; interface growth ; Laplacian growth ; linear stability analysis
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We develop a Laplacian model of interface growth which includes basic features of the anodisation of silicon in hydrofluoric acid. Our aim is to find mechanisms for the characteristic properties of porous silicon formation, such as the transition from electropolishing to pore formation and the typical pore distance. The local etching rate of the interface between the semiconductor and the electrolyte is determined by the local current density. We model the diffusive transport of charge carriers in the semiconductor and of reactants in the electrolyte including the basic features of the electrochemical reaction at the interface. A linear stability analysis of a flat and planar interface is performed in order to study the initial state of pore formation.
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  • 49
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    Journal of porous materials 7 (2000), S. 357-361 
    ISSN: 1573-4854
    Keywords: porous silicon ; X-ray diffraction ; differential scanning calorimetry
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The structural properties of (111) oriented p+ type Porous Silicon (PS) samples are investigated using various X-ray diffraction techniques and compared to (001) p+ type PS layer structure. High resolution X-ray diffractometry was used to record rocking curves and reciprocal space maps, giving indications about the crystalline quality of the PS samples as well as about the pore orientation. X-ray diffraction and reflectivity performed on thin PS layers allow to estimate the layer thickness, porosity and roughness of the PS/substrate interface.
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  • 50
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    Cytotechnology 34 (2000), S. 131-139 
    ISSN: 1573-0778
    Keywords: apoptosis ; bcl-xL ; cell growth ; cell viability ; hybridoma ; myeloma
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    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract While the ectopic expression of the anti-apoptoticprotein Bcl-2 has been shown to significantly increaseboth cell viability and antibody production in batchculture, some cell lines are refractory to thesemanipulations. For example, the NS/O and theP3x63Ag8.653 murine myelomas, which express highendogenous levels of the Bcl-2 homologue Bcl-xL, areboth resistant to the anti-apoptotic effect of Bcl-2.This indicates that, in these cells, Bcl-2 and Bcl-xLmay be functionally redundant. In order to define therole which Bcl-xL plays in hybridoma cultures, we usedthe Sp2/0-Ag14 cell line. This murine hybridomaexpresses low levels of Bcl-xL and is highly sensitiveto apoptosis induction by cycloheximide (CHX) and byamino acid depletion. Bcl-xL-transfected Sp2/0-Ag14cells were more resistant than the wild type and theplasmid-containing cells to apoptosis induced by CHXand by glutamine depletion. Moreover, when compared tothe vector-transfected control, Bcl-xL-Sp2/0 cellsexhibited a substantial increase in viability instationary batch culture. Interestingly, Sp2/0-Ag14cells overexpressing Bcl-xL showed a growth behaviourthat was similar to the parent myeloma cell lineP3x63Ag8.653. Our results suggest that Bcl-xLexpression levels are sufficient to account for therelative robustness of some hybridoma cell lines instationary batch cultures.
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  • 51
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    Journal of porous materials 7 (2000), S. 107-110 
    ISSN: 1573-4854
    Keywords: porous silicon ; conductivity ; percolation
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The AC conductivity of a percolation model with local energetical disorder for porous Silicon in three dimensions, σ(ω), is studied by Monte Carlo simulations. The model includes both diffusion and recombination processes and σ(ω) is obtained by a Fourier transform of the mean-square displacement of the carriers, where hopping diffusion of a single type of carrier (either an electron or an exciton) and two types of carriers (an electron and a hole) are considered. It is found that at low temperatures, the behavior of σ(ω) depends sensitively on the type of carrier considered.
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  • 52
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    Journal of porous materials 7 (2000), S. 233-237 
    ISSN: 1573-4854
    Keywords: porous silicon ; integrated optics ; wave guides
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this work we report a principle that allows one to write visible light emitting silicon patterns of arbitrary shape down to the sub-micrometer scale. We demonstrate that porous Si growth can electrochemically be initiated preferentially at surface defects created in an n-type Si substrate by Si++ ion bombardment. Using a focused ion beam (FIB) as a source of ions, arbitrary defect patterns can be written into a substrate. The growth of light emitting porous silicon is then selectively achieved by an electrochemical treatment which triggers Si dissolution only at these defect sites. The selectivity of the electrochemical dissolution reaction can be attributed to a facilitated Schottky barrier breakdown at the implanted surface defects which leads to the desired pore formation in confined surface areas.
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  • 53
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    Journal of porous materials 7 (2000), S. 267-270 
    ISSN: 1573-4854
    Keywords: porous silicon ; photoluminescence ; electroluminescence ; band structure ; experimental
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Electroluminescence, photoluminescence, and current-voltage measurements have been carried out on a series of samples consisting of porous silicon on top of crystalline silicon. The electroluminescence spectral distributions are markedly shifted towards long wavelengths in comparison to those seen with photoluminescence. The results are discussed and explained in terms of the energy-band structure of porous silicon. The problem of injecting electrons as well as holes into the porous silicon layer is pointed out and discussed.
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  • 54
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    Journal of porous materials 7 (2000), S. 315-318 
    ISSN: 1573-4854
    Keywords: porous silicon ; nonradiative ; radiative recombination
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An experimental investigation of the general characteristics of nonradiative and radiative recombination of charge carriers in strongly excited porous silicon is presented. It is shown that photoconductivity, photomagnetoelectric effect, quantum yield, and intensity of visible radiation of porous silicon demonstrates strong nonlinearities against laser excitation intensity. It is suggested that the band-to-band Auger recombination is dominant similar to that in crystalline silicon, whereas the visible luminescence is determined by the bimolecular process. The nonequilibrium density of charge carriers Δn ≈ 1019 cm−3, and the bimolecular radiative recombination coefficient Brad ≤ 9 × 10−14 cm3/s have been found.
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  • 55
    ISSN: 1573-4854
    Keywords: porous silicon ; thermal annealing ; nuclear magnetic resonance spectroscopy ; infrared spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract 29Si nuclear magnetic resonance (NMR) spectra and infrared spectra were measured for as-prepared and annealed porous silicon (PS) samples to characterize the change of PS structure. Annealing changed the infrared spectra remarkably: after 4-h annealing, the signals due to SiH2 disappeared and the intensity of the signals due to SiH decreased. On the other hand, the 29Si NMR spectra with magic-angle spinning (MAS) were not much affected by the annealing. The linewidth of spectra without MAS, however, increased with annealing time with the peak location unchanged. Annealing caused hydrogen on the PS surface to be desorbed, especially in the case of SiH2 species, and (SiH)2 dimer structure was produced during the annealing.
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  • 56
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    Journal of porous materials 7 (2000), S. 335-338 
    ISSN: 1573-4854
    Keywords: porous silicon ; oxidation ; calorimeter ; desorption ; activation energy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation of porous silicon has been studied using differential scanning calorimeter. The oxidation was found to consist of two parts with different activation energies. This indicates the existence of two different reaction mechanism. The results from the hydrogen desorption measurements have been used to study the different oxidation behaviour of the n- and p+-type porous silicon. The results show that the dihydride structure dominates on the surface of the n-type porous silicon, contrary to p+-type porous silicon, where the monohydride is the major structure. Explanations of these features are discussed. Using the activation energy, the surface termination effects are investigated. The best improvement in the activation energy was observed in the sample, whose surface was partially stabilized by ammonium groups.
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  • 57
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    Journal of porous materials 7 (2000), S. 381-383 
    ISSN: 1573-4854
    Keywords: porous silicon ; microstructure ; infrared spectroscopy
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We have investigated the effect of light exposure and ultrasonic (US) treatment on the formation of porous Si layers grown by electroless stain-etching technique. It was shown that; the He-Ne laser exposure resultedin a considerable increase in both the hydrogenation and the oxidation amounts in n-type Si, but a decrease in p-type wafers. The effect is attributable to effective change in the concentration of free hole carriers. The UV light exposure has led to the shift at the peak positions, indicating probably a change in bonding configuration, and increase in oxidation. Also, a correlation was established between the ultrasonic treatment and the microstructure. The US treated samples exhibit a decrease in hydrogenation and oxidation. UV exposure together with the US has led to a further decrease in both hydrogen and oxygen amounts, which was rather indicative of an excessive surface etching.
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  • 58
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    Journal of porous materials 7 (2000), S. 385-388 
    ISSN: 1573-4854
    Keywords: hydrogen desorption ; photoluminescence decay ; porous silicon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The decay under illumination of the photoluminescence (PL) intensity ofn-type porous silicon (PS) samples prepared by electrochemical etching has been investigated. We have found that the PL evolution with illumination time presents two different stages: an initial very fast decay which lasts ∼300 s, followedby a second one, much slower, which extends for times longer than 104 s. Thisevolution suggests that two different mechanisms could be responsible for the PLintensity decay. Samples subjected to different illumination times were studied byThermal Desorption Spectroscopy (TDS). The desorption rate of H2 and SiHx species was monitored during linear heating of the samples. A qualitative correlationbetween the decay of the PL intensity under illumination and the amount of H2 and SiHx species evolved from the illuminated samples has been observed. Experimentaldata suggest that H2 could be desorbed from the sample during the illuminationtime through a photoinduced H2 desorption process, inducing the decrease of the PLintensity.
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  • 59
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    Journal of porous materials 7 (2000), S. 323-326 
    ISSN: 1573-4854
    Keywords: positron annihilation ; porous silicon
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Positron lifetime spectroscopy has been used to investigate a porous silicon film subjected to heat treatments up to 1170°C. Annealings between 300 and 500°C resulted in a 17% mass increase of the film due to oxygen uptake following the effusion of hydrogen. The positron data also indicate that vacancy clusters are formed in the silicon oxide layer or the silicon oxide—silicon interface surrounding the nanocrystallites as oxygen replaces the effusing hydrogen. The vacancy cluster concentration, which may have a bearing on the photoluminescent properties, increased by a factor of three with heating to 500°C and then decreased to one-third the original value at higher temperatures. Above 900°C vacancy migration and clustering occurred, accompanied by visible deterioration of the film.
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    Journal of porous materials 7 (2000), S. 339-343 
    ISSN: 1573-4854
    Keywords: porous silicon ; infrared spectroscopy ; oxidation
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The Si–Si vibrational states near the surface region of porous silicon has been characterized using Fourier Transform Infrared Spectroscopy (FTIR) due to its enlarged surface area. By means of anodic etch and oxidization experiments, two Si–Si vibration modes of porous silicon have been identified as near the surface regions and in the bulk, respectively. The intensity of absorption peak at 620 cm−1, which originates from the Si–Si bonds vibrations on the surface and near surface regions of porous silicon, is found to vary depending on the length of etch and degree of oxidation of porous silicon, which exists before etching and is recovered again after fully oxidation. The peak of 610 cm−1 doesn't change throughout the oxidation experiment, and to be assigned for Si–Si bond vibrations in the bulk. With an extra irradiation of Nd:Yag laser on the PS sample the Raman and FTIR spectra reveal a red shift. These results can give an interpretation to explain the different phenomenon of Si–Si vibrations of Raman and FTIR spectroscopy.
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    Journal of porous materials 7 (2000), S. 367-371 
    ISSN: 1573-4854
    Keywords: porous silicon ; luminescence ; light assisted chemical etching
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    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A new approach to the problem of preparation of laterally structured luminescent porous silicon is proposed. The effect is based on the photosensitivity of chemical etching of silicon. Contrary to the other technique recently reported where the porous layer was modified with light assisted chemical dissolution, a one stage anodisation-free process is used. Any desired lateral structure can be produced, depending on the illumination pattern, which is defined by optical imaging. A 2D micro-array was prepared as an example of this fast mask-free technology with an accuracy of 5 μm. Samples have a broadband visible photoluminescence centred at 680 nm when illuminated with UV or blue light. The results are analysed to determine the possible achievable accuracy of the technique and to improve our understanding of the mechanism of light assisted etching.
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    Journal of porous materials 7 (2000), S. 397-400 
    ISSN: 1573-4854
    Keywords: porous silicon ; Raman spectroscopy ; immersion plating ; silver
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    Notes: Abstract Raman scattering from porous silicon layer into which silver is immersion-plated was studied. Ag-deposited samples show extra Raman bands. Heat treatment of the Ag-deposited samples results in a great decrease in such Raman bands. Also dipping in hydrofluoric acid solution causes a spectral change. Some comments on the assignment of the Raman peaks of the Ag-deposited porous silicon are given, and the structure of porous silicon on which metal is immersion-plated is discussed.
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  • 63
    ISSN: 1573-0778
    Keywords: antisense ; apoptosis ; cell cycle ; c-jun ; protein production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract Expression of c-jun gene induces apoptosis ofcells cultured in serum-free medium. It also promotescell-cycling in serum-containing medium, leading cellsto die by overgrowth. Previously, we established anapoptosis-suppressible, cell-cycle arrestable cellline, c-jun AS, by transfecting Friend murineerythroleukemia (F-MEL) cells with adexamethasone-inducible antisense c-jun gene.Induction of the antisense c-jun transcriptionwith dexamethasone suppressed c-jun expression.As a result, c-jun AS cells survived inserum-free medium containing dexamethasone for a longtime, while F-MEL cells died quickly in the presenceor absence of dexamethasone. In serum-containingmedium, the growth of c-jun AS cells was viablyblocked by inducing antisense c-juntranscription, and the cells survived at thenon-growth state avoiding overgrowth. In the presentstudy, protein productivity of c-jun AS cellswas examined in comparison with that of wild typeF-MEL cells. C-jun AS and F-MEL cells werefurther transfected with a vector for expressingalkaline phosphatase as a protein to be produced, andnamed c-jun AS-SEAP and F-MEL-SEAP cells,respectively. In the serum-free medium withdexamethasone, c-jun AS-SEAP cells produced theprotein for up to 6 days, while F-MEL-SEAP cellsstopped production on day 3 due to cell death causedby serum deprivation. In the serum-containing mediumwith dexamethasone, c-jun AS-SEAP cells wereviably arrested in the cell cycle, and cell death dueto overgrowth was avoided. As the result, they couldproduce the protein for up to 18 days, whileF-MEL-SEAP cells stopped production within 7 days dueto cell death caused by overgrowth.
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  • 64
    ISSN: 1573-4854
    Keywords: porous silicon ; photoluminescence ; synchrotron radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Using synchrotron as a tunable excitation source, we have carried out a study on the photoluminescence systematics from a series of porous silicon samples prepared under different conditions, Luminescence spectra were recorded with excitation photon energies tuned to the Si L3,2 absorption edge (∼100 eV). The luminescence yield was in turn used to monitor the Si L3,2-edge absorption characteristics of porous silicon. A trend of luminescence wavelength and intensity as a function of preparation conditions emerges. Other related observations are also noted.
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  • 65
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    Journal of porous materials 7 (2000), S. 191-195 
    ISSN: 1573-4854
    Keywords: cell growth ; porous silicon ; cytotoxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The paper reports the results of the study of cell culture growth at the surface of porous silicon. They show that porous and poly(nano)crystalline Si offer significant advantages over bulk Si surfaces for cell adherence and viability: these materials do not require coating with substances such as polylysine to support cell growth; porous Si is light-addressable because of photoluminescence and photovoltaic effects noted [Unal and Bayliss, J. Appl. Phys. 80, 3532 (1996)], allowing the potential for optical data transfer and less susceptibility to interference from external electronic equipment; finally nanostructured coatings can be applied to most object shapes, giving flexibility in their application.
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  • 66
    ISSN: 1573-4854
    Keywords: porous silicon ; superlattices ; photoluminescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Porous silicon photoluminescence and electroluminescence can be controlled by periodically modulating the material porosity to form high quality multilayer stacks and microcavities. Important issues not yet fully addressed are (a) the precise role played by this microstructuring, given that the luminescence is distributed throughout the entire structure and that the low porosity layers are highly absorbing at short wavelengths, and (b) whether the quality of such microcavities could be sufficient to support lasing. Using both experimental and theoretical techniques, the emission and reflection properties of different porous silicon single and multilayer structures have been investigated in order to understand further and exploit the nature of light propagation within them.
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  • 67
    ISSN: 1573-4854
    Keywords: porous silicon ; patterning ; photolythography dielectric filters ; reactive ion etching (RIE) ; microoptics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Porous silicon (PS) layer systems have a broad range of possible applications. An advantage is the good control of the refractive index and the etch rate of the layers by the applied current density and the time respectively. For micro-optical devices you need patterned PS. For some optical devices it is not sufficient to have only one filter but it is necessary to form filters with different properties on a small area. We applied a method (M. Frank, U.B. Schallenberg, N. Kaiser, and W. Buß, in Conference on Miniaturized Systems with Microoptics and Micromechanics, edited by M.E. Moamedi, L.J. Hornbeck, and K.S.J. Pister (SPIE, San Jose, 1997), SPIE Proceedings Series 3008, p. 265) to PS which fits this goal by the following steps: fabrication of the desired reflectors below each other and partial removal of upper reflectors with reactive ion etching (RIE). The technological aspects of patterning PS after the fabrication are an important topic of this work. Problems are discussed in detail and solutions are given.
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  • 68
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    Journal of porous materials 7 (2000), S. 115-118 
    ISSN: 1573-4854
    Keywords: porous silicon ; synchrotron radiation ; coulomb blocade
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this paper we demonstrate that photo-electron emission excited by X-UV synchrotron radiation can be used as a “contactless” probe of the gross conduction processes in porous silicon. Moreover we demonstrate that this approach reveals the underlying conduction geometry. We show that conduction in porous silicon is to some degree controlled by percolation phenomena and finally present data which support the notion that the fundamental blocking process may be Coulomb Blockade [P.A. Lee, Physica B 189, 1–5 (1993); D. Ali and H. Ahmed, Appl. Phys. Lett. 64, 2119–2120 (1994)].
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  • 69
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    Journal of porous materials 7 (2000), S. 263-266 
    ISSN: 1573-4854
    Keywords: porous silicon ; time-resolved photoluminescence ; decays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Porous silicon has been studied with time-resolved photoluminescence, and growth as well as decay curves have been measured at several detection energies, with sample temperatures between 10 and 300 K. In the decay curves, three components are mainly observed, a small one which is very fast, with time scales of the order of nanoseconds or faster, the main component having time scales of the order of milliseconds, and a very small, very slow component, with time scales of the order of seconds. The main components can in most—but not all—cases be fitted well with stretched exponentials containing two fitting parameters. Of these, it comes out that the parameter accounting for disorder or the like depends only little upon detection energy and temperature, whereas the parameter accouting for the development in time decreases substantially for increasing temperature. The results are discussed.
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  • 70
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    Journal of porous materials 7 (2000), S. 279-282 
    ISSN: 1573-4854
    Keywords: porous silicon ; optical absorption ; theoretical modelling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The optical properties of porous silicon (p-Si) are calculated from the electronic band structure obtained by means of an sp3s* tight-binding Hamiltonian and a supercell model, in which the pores are columns detched in crystalline silicon (c-Si). The disorder in the pore sizes and the undulation of the silicon wires are considered by the existence of arandom perturbative potential, which produces non-vertical interband transitions, otherwise forbidden. A typical interval around each k-vector (optical window), where non-vertical transitions make an important contribution, depends on the value of the disorder and its order of magnitude is given by l−1, where l is the localization length. The calculated absorption spectra are compared with experiments, showing good agreement.
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  • 71
    ISSN: 1573-4854
    Keywords: nanocrystalline silicon ; porous silicon ; cathodoluminescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Luminescence emission of LPCVD polycrystalline silicon films has been studied by cathodoluminescence (CL) in the scanning electron microscope. As-deposited films show visible luminescence with dominant blue band. The relative intensity of blue emission is enhanced by implantation and by slight anodization treatments. Our investigations are consistent with previous PL results and indicate that the origin of blue emission is related to quantum confinement effects. On the other hand, the effect of annealing in these samples is a reduction of the CL signal that could be related to the increase of the nanocrystals size.
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  • 72
    ISSN: 1573-4854
    Keywords: porous silicon ; photoacoustic spectroscopy ; energy band
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Porous silicon has been studied with photoluminescence, photoluminescence excitation, and photoacoustic spectroscopy. From the luminescence data, an energy-level diagram related to the luminescence is constructed. The diagram is confirmed in detail by the photoacoustic spectra. The results are discussed with the conclusion that they are in good agreement with the surface-band oxyhydride-like emitter, which recently has been established as the source for the photoluminescence from porous silicon.
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  • 73
    ISSN: 1573-4854
    Keywords: porous silicon ; Raman spectroscopy ; morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Raman-light scattering in porous silicon samples with oriented quantum wires was studied. It was shown, that the experimental data depends on the type of organization of wire system. The explanation of observed effect is discussed.
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  • 74
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    Journal of porous materials 7 (2000), S. 287-290 
    ISSN: 1573-4854
    Keywords: porous silicon ; sensors ; gas absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this paper we report the sensitivity of porous silicon photoluminescence (PL) to diluted mixtures of methane and carbon monoxide in synthetic air. We also investigate the separate effect of synthetic air, purified nitrogen and relative humidity on both photoluminescence and conductance (G). Porous silicon samples have been prepared from n-type silicon substrates. We find that PL intensity and G decrease in synthetic air with respect to their values in N2. Presence of carbon monoxide reduces the PL intensity while methane provokes the opposite behaviour. The dependence of the PL spectra on methane and carbon monoxide concentrations has been investigated. The observed effects can be related to gas induced modifications in porous surface and suggest that porous silicon can be employed in gas sensor technology.
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  • 75
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    Journal of porous materials 7 (2000), S. 299-301 
    ISSN: 1573-4854
    Keywords: porous silicon ; Schottky emission ; photoluminescence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Electrical transport in Gold/porous silicon/crystalline silicon junctions has been studied. The junctions are found to improve when the porous silicon is exposed to a hydrogen plasma before depositing the top metal. The hydrogen passivated junctions exhibited higher current levels and emitted light at lower voltages as compared to the unhydrogenated ones. Internal photoemission measurements were carried out to investigate the gold/porous silicon barrier. The barrier height determined from the Fowler plot is independent of the top material. The temperature dependence of the barrier height is similar to that of the crystalline silicon energy gap.
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  • 76
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    Journal of porous materials 7 (2000), S. 11-16 
    ISSN: 1573-4854
    Keywords: porous silicon ; kinetics electrochemistry ; etching ; surface analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The electrochemistry of porous silicon formation has been investigated by different electrochemical as well as surface analytical methods. The kinetics of pore nucleation was observed as small steps in fast current and potential pulse transients. Oxidic intermediates were identified by ex-situ XPS. Cyclic voltammetry in solutions of different HF concentration was correlated with the etching rate of silicon dioxide. On the basis of these experimental data, an electrochemical model for the porous silicon formation is presented.
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  • 77
    ISSN: 1573-4854
    Keywords: porous silicon ; four-wave mixing ; microwave harmonics generation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We apply optical contactless techniques, namely the four-wave-mixing and microwave harmonics generation for the characterization of nanocrystalline free-standing films and platelets of microcrystalline porous silicon. We observe (i) full carrier localization and significant lifetime shortening in free-standing films, which is thought to be a manifestation of their low-dimensional confinement, (ii) increased carrier lifetime in microcrystalline porous silicon, presumably originating from passivated surface states at the surface of pores.
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  • 78
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    Journal of porous materials 7 (2000), S. 407-410 
    ISSN: 1573-4854
    Keywords: porous silicon ; stain etching ; morphology ; HREM ; reflectance spectrometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Porous silicon films, nearly 100 nm thick, were produced by stain etching of n+-type silicon substrates. The films were studied by a non-destructive technique: dielectric function profiles were deduced by spectral reflectance via a finite difference model, and porosity was computed by the Effective Medium Approximation. The obtained information, combined with High Resolution Electron Microscopy observations,provided a deeper insight on the relations among technological process, morphology and reflective properties. Our preliminary results outline the possibility to control the porosity profile as well the reflectance of the porous films via the oxidising species concentration in the stain etching solution.
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  • 79
    ISSN: 1573-4854
    Keywords: stain etching ; porous silicon ; neutron reflection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We have monitored the stain-etching of silicon in real time using neutron reflection. The etching process does not occur uniformly with time and possible dynamics of the process is under consideration. Distinct irregularities are produced on the PS surface and some gas bubbling from the cell is observed.
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  • 80
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    Journal of porous materials 7 (2000), S. 77-80 
    ISSN: 1573-4854
    Keywords: porous silicon ; ZnSe ; electrochemical deposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Electroplating of II-VI semiconductors like ZnSe into porous silicon can be an efficient and low cost method to fill the porous volume with a transparent and conductive material. With n-type porous layers, ZnSe impregnation is more effective near the sample surface because of reaction rate limitations due to diffusion in the electrolyte. In this paper, it is shown that the deposition of ZnSe into p-type porous silicon can be localized in the lower part of the porous layer if the reduction reaction rate is monitored by limiting the charge carrier supply. This can be done by controlling the power of the laser beam which photo-generates the carriers at the bottom of the pores. Studying the porous layer chemical composition by Auger electron spectroscopy confirms that the deposit is localized at the pore bottom, whereas the changes in the chemical composition of the porous silicon surface are analyzed by infra-red spectroscopy.
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  • 81
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    Journal of porous materials 7 (2000), S. 97-101 
    ISSN: 1573-4854
    Keywords: AC impedance ; porous silicon ; residual moisture ; aging effects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The present work aims to study the AC impedance of porous silicon films left in the contact with the anodizing bath after their growth is over. It is shown that the layers grown at p-type silicon experience noticeable changes of their impedance behavior resulting in the gradual growth of electrical resistance of the p-PS layer. This change is assumed to be related with the deposition of a passive layer at the pore bottoms associated with reabsorption of dissolved Si-containing material from the electrolyte. The layers formed at n-Si also show changes of the electrical impedance, although they are much more complicated than in the previous case (dependence of the kinetics of changes on the polarization current and polarization time, presence of the inductive loops at the impedance spectra, etc.
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  • 82
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    Journal of porous materials 7 (2000), S. 169-172 
    ISSN: 1573-4854
    Keywords: EXAFS ; XEOL ; porous silicon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Results of an EXAFS investigation on porous Silicon carried out by X-ray Excited Optical Luminescence (XEOL) and Total Electron Yield (TEY) techniques, at the Si K absorption edge, are reported. For the first time XEOL spectra of porous silicon have been recorded in a wide energy range (1800–2500 eV) and EXAFS signals have been singled out from them. Simultaneous TEY and XEOL measurements yield to different results: in particular TEY-EXAFS is sensitive up to the third coordination shell of Si, while XEOL-EXAFS reveals only the contributions of the first two coordination shells; moreover they show a different dependence on changes of the etching parameters. This evidences the sensitivity of XEOL technique to the local structure of the quantum confined luminescent sites. The dependence of the light emission properties on the main preparation parameters and their influence on the short-range structure of red and yellow porous silicon samples are also investigated.
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  • 83
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    Journal of porous materials 7 (2000), S. 187-190 
    ISSN: 1573-4854
    Keywords: porous silicon ; temperature programmed desorption ; FTIR ; silane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The gaseous species desorbed from porous silicon (PS) were investigated using the method of temperature programmed desorption (TPD) and fourier transform infrared spectroscopy (FTIR). Silicon wafers (25–50 Ω cm, p−, FZ) were anodised in 40% HF and HF/C2H5OH electrolytes. The PS samples were linearly heated at 1.5 K s−1 using a custom built heating unit in a oil-free pump backed vacuum chamber at a base pressure of 〈10−8 torr. A quadrupole mass spectrometer, which was used as the detector, was fitted in line of sight of the sample at a distance of about 6 mm. It was observed that silane was liberated during the heating of porous silicon samples produced from both electrolytes. The peak temperature at which this occurred was at 570 ± 10 K. This temperature coincides with the temperature of silicon-silicon bond breakage in ≡Si–SiH3 groups on the pore walls, as shown by the FTIR results. It is proposed that silane formation involves the reaction of the Si-silyl group with moisture: ≡Si–SiH3 + H2O → ≡Si–OH + SiH4.
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  • 84
    ISSN: 1573-4854
    Keywords: porous silicon ; oxidation ; liquid crystal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this paper we demonstrate the filling of porous silicon (PS) layers with liquid crystals (LC's) in order to control the reflectance electrically. The preparation of PS and the choice of the right group of LC's will be presented. Especially an oxidation of PS is necessary so that the methods and parameters of oxidation will also be discussed. As a first result the increasing and decreasing of the thickness oscillations in the reflectance as a function of the applied voltage can be observed.
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    Journal of porous materials 7 (2000), S. 227-231 
    ISSN: 1573-4854
    Keywords: porous silicon ; micromachining ; localised anodisation ; fibre positioning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Low-loss optical fibre connections require deep grooves etched in silicon substrate for accurate fibre positioning. As shown in this paper these grooves can be obtained by using localised formation of porous silicon on patterned substrates. Cr-Au masking layer with a duration in HF solution longer than 30 min is used to fabricate grooves with a depth higher than 75 μm. N+-type silicon provides grooves with a pseudo-V shape which is compatible with accurate fibre alignment. By using this technology, arrays of optical fibres are positioned with an accuracy higher than 1 μm.
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    Journal of porous materials 7 (2000), S. 243-246 
    ISSN: 1573-4854
    Keywords: porous silicon ; oxidation ; refractive index ; optical waveguide ; optical losses
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Further results on the optical properties of oxidised porous silicon as a function of porosity and oxidation conditions are presented in this paper. The refractive index varies logarithmically with the oxidation time irrespective of the porosity of the sample and the oxidation temperature. Burried waveguides have been realised from as-prepared and oxidised porous silicon. Optical losses of 18 dB cm−1 at λ = 1.3 μm have been obtained after oxidation at 800°C for 35 min.
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  • 87
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    Journal of porous materials 7 (2000), S. 119-123 
    ISSN: 1573-4854
    Keywords: porous silicon ; light-emitting diode ; series resistance ; external quantum efficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract In this paper, two novel structures of porous silicon (PS) light-emitting diodes (LEDs) are proposed aiming at the reduction of series resistance, Rs. The basic idea of the novel structures is to suppress the excessive growth of nanoporous silicon (nano-PS) layer that is electroluminescence- (EL-) active but highly resistive. The initial wafer of the first structure consists of a lightly-doped layer stacked on a highly-doped substrate. As a consequence of anodization, nano-PS layer is formed only in the lightly-doped layer, while meso-PS layer with moderate resistivity is formed in the highly-doped substrate. The second structure consists of alternately stacked nano- and meso-PS layers, since it is expected that multiple thin nano-PS layers connected in series are less resistive than a single thick nano-PS layer. Preliminary experimental results proved the effectiveness of these novel structures on the reduction of Rs.
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    Journal of porous materials 7 (2000), S. 271-273 
    ISSN: 1573-4854
    Keywords: porous silicon ; photoconductivity ; energy band gap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Photocurrent measurements have been carried out on a series of samples consisting of porous silicon on top of crystalline silicon, in the temperature range 10–300 K. From the experimental data set, the electrical band-gap energy of porous silicon is deduced to be (1.80 ± 0.01) eV, independent of sample temperature. The results are discussed with the conclusion that for the samples studied here, the electrical bandgap in porous silicon is of molecular nature and cannot be related to quantum-confinement properties of nanocrystals of elemental silicon.
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  • 89
    ISSN: 1573-4986
    Keywords: sialidase ; sialyltransferase ; apoptosis ; Jurkat cells ; etoposide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The present study investigated the mechanism underlying alterations of cell surface sugar chains of Jurkat cells by inducing apoptosis with etoposide, an inhibitor of topoisomerase II. Within 3[emsp4 ]h of etoposide treatment, flowcytometric analysis revealed a decrease in Maackia amurensis agglutinin recognized α2,3-linked sialic acid moieties and an increase in Ricinus communis agglutinin recognized galactose. The results suggested that asialo-sugar chains on glycoconjugates were rapidly induced on the etoposide-treated cell surface. To clarify the desialylation mechanism, we studied α2,3-sialyltransferase mRNA expression and the activity of sialidase on the cell surface during etoposide-induced apoptosis. The expression of hST3Gal III and hST3Gal IV mRNAs were down-regulated and sialidase activity on the cell surface increased threefold within 2[emsp4 ]h of etoposide treatment. Moreover, the decrease in α2,3-linked sialic acid levels was significantly suppressed in the presence of 2,3-dehydro-2-deoxy-N-acetylneuraminic acid, an inhibitor of sialidase. These results suggested that activation or exposure of sialidase on the cell surface was induced by etoposide treatment and was the main cause of the decrease in sialic acids.
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  • 90
    ISSN: 1573-8469
    Keywords: apoptosis ; bacteria ; chromatin condensation ; DNA degradation analysis ; plant ; programmed cell death
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Ultrastructural details of the hypersensitive reaction induced by infiltration with avirulent race 2 Xanthomonas campestris pv. vesicatoria in pepper ‘Early Calwonder-10R’ leaves (incompatible interaction) are reported. Affected cells displayed plasmalemma undulations and disruption, lysis of the chloroplast membrane, degeneration of other organelles, general cytoplasm disorganisation and, often, protoplast shrinkage. The nuclei contained large masses of electron-dense material, apparently formed by chromatin aggregation. In many cases a single chromatin-like layer was deposited on the inner side of the nuclear envelope leaving a finely granular matrix in the centre of the nucleus; the nucleolus usually disappeared. The nuclear envelope was sometimes ruptured and the internal matrix leaked into the cytoplasm. The content of many affected cells eventually coagulated and became very electron-dense. The walls often collapsed. All these alterations were especially visible in spongy mesophyll cells at sites where bacteria occurred in the intercellular spaces. Although some of the nuclear and cytoplasmic alterations recall certain aspects of apoptotic cell death, molecular determinations did not reveal any DNA degradation in hypersensitively reacting tissues. The first cell alterations in leaves infected with the virulent bacterial race 1 (compatible interaction) were observed only 27 h after inoculation, when the cytoplasm of some cells showed limited internal disorganisation and plasmolysis at sites where bacterial colonies developed.
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    Apoptosis 5 (2000), S. 203-209 
    ISSN: 1573-675X
    Keywords: apoptosis ; lens development ; organelle loss ; denucleation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The lens represents an ideal model system for studying many of the cellular and molecular events of differentiation. It is composed of two ectodermally-derived cell types: the lens epithelial cells and the lens fibre cells, which are derived from the lens epithelial cells by differentiation. Programmed removal of nuclei and other organelles from the lens fibre cells ensures that an optically clear structure is created, while the morphology of the degenerating nuclei is similar to that observed during apoptosis and is accompanied by DNA fragmentation. These observations suggest the existence of biochemical parallels between the process of lens fibre cell organelle loss and classical apoptosis. For example, proteins encoded by the bcl-2 and caspase gene families are expressed in developing lenses and nuclear degeneration in lens fibre cells can be inhibited in vivo by overexpression of bcl-2 and in vitro by incubation of differentiating lens epithelial cell cultures with caspase inhibitors. Thus, the developing lens may represent a particularly useful model system for researchers interested in apoptosis. In this review, the recent literature pertaining to lens fibre cell organelle loss and its relationship to apoptosis is reviewed and possible future research directions are suggested.
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    Apoptosis 5 (2000), S. 217-220 
    ISSN: 1573-675X
    Keywords: Daxx ; apoptosis ; Fas ; PML ; ND10
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Several reports describing Daxx and its putative role have emerged without a unifying theme. While Daxx has been implicated in apoptosis, it remains unclear whether Daxx is pro- or anti-apoptotic, and whether its role in apoptosis is direct or indirect. Moreover, whether Daxx plays alternative or additional roles in regulating transcription, centromere binding or any number of other activities within the cell, is uncertain. The ability of Daxx to interact with a wide variety of molecules in yeast-interaction trap systems (Table 1) has allowed for this range of speculation. The fact that Daxx contains no significant homology to other known proteins has rendered its study all the more challenging.
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  • 93
    ISSN: 1573-675X
    Keywords: apoptosis ; cyclin B1/CDC 2 ; G2/M arrest ; MAD 2 ; paclitaxel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Paclitaxel (Taxol™) is a microtubule-interfering agent that induced persistent and transient G2/M arrest before apoptosis in human nasopharyngeal carcinoma (NPC) cells at high and low concentrations, respectively. In this study, we intended to explore the underlying molecular events and found that cellular cyclin B1/CDC 2 kinase activity was increased and persisted for 〉6 h upon paclitaxel treatment both at high and low concentrations. Furthermore, activation of MAD 2 checkprotein could account for the loss of cyclin B1 ubiquitination and the persistence of cyclin B1/CDC 2 activation in the cases. To investigate the involvement of cyclin B1 and MAD 2 activation in paclitaxel-induced apoptosis, we introduced affinity-purified anti-cyclin B1 and MAD 2 antibodies into NPC cells by electroporation before the further paclitaxel treatment. The antibodies against cyclin B1 and MAD 2 indeed attenuated paclitaxel-induced cytotoxicity and DNA fragmentation. Our study suggests that activation of cyclin B1/CDC 2 and MAD 2 were the M-phase events required for paclitaxel-induced apoptosis in NPC cells. The dys-regulated cyclin B1/CDC 2 activation could enhance the prometaphase progression, but activation of MAD 2 rendered cells inable to exit from the metaphase. Under this circumstance, cells were probably going to “mitotic catastrophe” and ultimately, destined to apoptosis.
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  • 94
    Electronic Resource
    Electronic Resource
    Springer
    Apoptosis 5 (2000), S. 211-215 
    ISSN: 1573-675X
    Keywords: adenovirus ; E4orf4 ; apoptosis ; protein phosphatase 2A (PP2A) ; caspases ; cancer ; gene therapy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Adenovirus E4orf4 protein is a multifunctional viral regulator that induces p53-independent apoptosis in transformed cells, but not in normal cells. E4orf4-induced apoptosis can occur without activation of known caspases, although E4orf4 induces caspase activity in some cell lines. The interaction of E4orf4 with a specific subpopulation of protein phosphatase 2A (PP2A) molecules that contain B subunits, but not with those that contain B′ subunits, is required for induction of apoptosis. This review suggests the potential use of E4orf4 in cancer therapy, and discusses whether E4orf4-induced apoptosis plays a role in the viral life cycle. Future research directions are also highlighted.
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  • 95
    ISSN: 1573-675X
    Keywords: Amphibia ; apoptosis ; cancer ; cell cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Spontaneous and induced cancers are rare in non-isogeneic or inbred amphibians. Neoplastic cells become immortalized through loss of a normal capacity to die by apoptosis. Mature lymphocytes of mammals require activation and entry into the cell cycle in order to become susceptible to apoptosis. Whether Xenopus lymphocytes differ from mammalian lymphocytes in this regard is examined. In vitro exposure of PMA, or its analogue, MPMA, to adult splenocytes of Xenopus laevis was used to affect apoptosis. Flow cytometric analysis of FITC-Annexin V/propidium iodide (PI) fluorescence (apoptosis) and BrdU uptake (DNA synthesis) were assayed concurrently in the same lymphocyte population over time. Significant increases in apoptotic levels were induced throughout a 72 hour period in PMA-treated cells only. Lymphocytes were also separated by size for analysis. Several sub-populations of lymphocytes were identified, the most interesting of which was small and apoptotic within 4 hours, after PMA exposure. PMA-induced DNA synthesis did not become elevated until after 24 hours. “Direct” apoptosis, i.e. without cell cycle entry, was found only in these small, mature lymphocytes. Since small lymphocytes make up the vast majority of those being analyzed, “direct” apoptosis may be a determining mechanism in the resistance to neoplasia observed in Amphibia. Cells that die more readily are less likely to transform into neoplastic cells.
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  • 96
    ISSN: 1573-675X
    Keywords: apoptosis ; caspase-3 ; nuclease ; endo-exonuclease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Single-strand DNase and poly rAase, activities characteristic of endo-exonuclease, were co-activated in nuclear fractions of HL-60 cells by caspase-3. Activation was accompanied by cleavages of large soluble polypeptides (130–185 kDa) and a 65 kDa inactive chromatin-associated polypeptide related to the endo-exonuclease of Neurospora crassa as detected on immunoblots. The major products seen in vitro were a 77 kDa soluble polypeptide and an active chromatin-associated 34 kDa polypeptide. When HL-60 cells were induced to undergo apoptosis by treating with 50 μM etoposide (VP-16) for 4 hours, 77 kDa and 40 kDa polypeptides accumulated in nuclear fractions. Chromatin DNA fragmentation activity was also activated in cytosol and nuclear extract either by pre-treating the cells in vivo with VP-16 or by treating the cytosol in vitro with caspase-3 or dATP and cytochrome c. Endo-exonuclease activated by caspase-3 in cytosol-derived fractions augmented chromatin DNA fragmentation activity in vitro. Endo-exonuclease is proposed to act in vivo in conjunction with the caspase-activated DNase (CAD) to degrade chromatin DNA during apoptosis of HL-60 cells.
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  • 97
    Electronic Resource
    Electronic Resource
    Springer
    Apoptosis 5 (2000), S. 307-314 
    ISSN: 1573-675X
    Keywords: apoptosis ; cancer ; cross-priming ; cross-tolerance ; dendritic cells ; T lymphocytes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Induction of cell death by apoptosis, also called programmed cell death, and clearance of apoptotic bodies by scavenger cells has long thought to be an efficient means to dispose of unwanted cells without causing inflammatory responses able to mediate specific reactions. However, a number of evidences have been accumulated suggesting that apoptotic cell death is implicated in the pathogenesis of systemic and organ specific autoimmune diseases. In addition, recognition and engulfement of apoptotic cells by professional antigen presenting cells, such as dendritic cells, and their interaction with effector immune cells have been recently described to result in apoptotic cell-derived antigen specific tolerance. This review will summarise the most recent findings on the immunogenic potential of cells undergoing programmed death.
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  • 98
    ISSN: 1573-675X
    Keywords: Angiogenesis ; angiopoietins ; apoptosis ; integrins ; vascular endothelial growth factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Angiogenesis is essential for the growth and metastasis of solid tumors. The balance of endothelial cell (EC) proliferation and apoptosis is a major determinant in tumor angiogenesis. Recently, several studies demonstrated that numerous angiogenic factors not only induce angiogenesis but also function as EC survival factors. Vascular endothelial growth factor (VEGF), a potent angiogenic factor, is also an EC survival factor in embryonic vasculogenesis and tumor angiogenesis. VEGF activates specific intracellular survival pathways in ECs including Bcl-2, A1, IAP, Akt, and Erk. Integrins may function as EC survival factors by preventing anoikis by enhancing binding to the extracellular matrix. In addition, integrins may function in concert with VEGF to promote EC survival. Angiopoietin-1 (Ang-1) has recently been shown to stabilize EC networks by binding to the EC-specific tyrosine kinase receptor Tie-2. Pericytes also function as EC survival factors, by cell-cell contact, secretion of survival factors, or both. Targeting any of the above mechanisms for EC survival may provide novel antineoplastic strategies.
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  • 99
    ISSN: 1573-675X
    Keywords: apoptosis ; antimicrotubule agent ; cell cycle ; dolastatin 10 ; TZT-1027
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract TZT-1027, a newly synthesized dolastatin 10 derivative, is a potent antitumor agent which inhibits microtubule polymerization and perturbs microtubule dynamics. In this report, we investigated whether TZT-1027 inhibited the growth of various human cancer cells, and the cell death caused by TZT-1027 was due to apoptosis. In addition, we elucidated the apoptosis machinery induced by treatment with TZT-1027. The 50% growth-inhibitory concentrations (IC50 values) of TZT-1027 on cancer cells derived from various sources were not more than 5.9 ng/ml. TZT-1027 showed superior cytotoxicity than any other antitumor agents. Next, we evaluated morphological nuclear change, namely, chromatin condensation and DNA fragmentation. We used three cancer cell lines derived from different types in view of having apoptosis related protein, human leukemia HL-60 (in the presence of both Caspase-3 and Bcl-2), human breast cancer MCF-7 (in the absence of Caspase-3), and human prostate cancer DU145 (in the absence of Bcl-2). TZT-1027 induced DNA fragmentation in the presence but not absence of Caspase-3. Nevertheless, apoptic chromatin condensation was observed in all cancer cells even if there was no Caspase-3. Furthermore, we examined whether TZT-1027, microtubule-disrupting agent, influenced cell cycle progression. Flow cytometric analysis revealed the cells treated with TZT-1027, and with the other antimicrotubule agents, to be arrested at the G2/M phase and subsequently to show fragmented DNA smaller than that of G1 phase cells. Moreover, we tested TZT-1027 for its ability to induce Bcl-2 phosphorylation in human cancer cell lines. TZT-1027 and other agents which interacted with microtubules induced Bcl-2 phosphorylation, whereas DNA-damaging agents did not. The present results suggested an association of the growth-inhibitory effect of TZT-1027 with the induction of apoptosis and indicated that the apoptosis induced by TZT-1027 was followed by G2/M arrest even if there was no Caspase-3 or Bcl-2.
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  • 100
    ISSN: 1573-675X
    Keywords: apoptosis ; chemotherapy resistance ; clonogenicity ; ras
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mutationally activated Ras is involved in tumor progression and likely also in drug resistance. Using survival, viability and apoptosis assays, we have here compared the cisplatin sensitivities of FR3T3 rat fibroblasts and a 12V-H-ras transformed subline (Ras2:3). Around 24 h after cisplatin treatment Ras2:3 cells showed higher apoptosis levels and lower viability than FR3T3. This increased sensitivity correlated with weaker cisplatin-induced activation of Jun N-terminal kinase (JNK). In contrast to apoptosis assays, colony formation assays showed that Ras2:3 were more resistant to cisplatin than were FR3T3. This was partly due to the increased cisplatin sensitivity of FR3T3 seeded at low densities, as required in colony formation assays. In addition, Ras2:3 cisplatin survivors had a higher relative proliferative capacity. Cell cycle analyses showed that FR3T3 cells initially responded with a dose-dependent G2 arrest, while Ras2:3 accumulated in S-phase. Experiments with an anti-apoptotic mutant of MEKK1 suggested that the apoptotic response of Ras2:3 cells is not specific to the S-phase fraction. In summary, the cisplatin response of ras-transformed fibroblasts is distinct from that of parental cells, in that they show increased apoptosis, a different cell cycle response and increased post-treatment proliferative capacity. The results illustrate the need to carefully consider methods and protocols for in vitro studies on chemotherapy sensitivity.
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