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981.
Mitotic chromosome number of 14 taxa of Bothriochloa native to Argentina, Brazil and Uruguay were surveyed. Chromosome numbers of B. eurylemma, B. meridionalis and B. velutina are reported for the first time, with 2n = 6x = 60, and this ploidy level is the most common among the studied taxa. In addition, new cytotypes were found for B. alta (2n = 60), B. barbinodis (2n = 60), B. exaristata (2n = 80), B. laguroides var. torreyana (2n = 80), B. longipaniculata (2n = 60 and 80), B. perforata (2n = 60) and B. springfieldii (2n = 60). These numbers differ from those reported in the literature. 相似文献
982.
983.
Pijlman GP de Vrij J van den End FJ Vlak JM Martens DE 《Biotechnology and bioengineering》2004,87(6):743-753
Continuous protein production with baculovirus expression vectors in insect-cell bioreactors is characterized by a dramatic drop in heterologous protein production within a few weeks. This is mainly due to the spontaneous deletion of the heterologous gene(s) from the baculovirus genome and/or to the rapid accumulation of defective interfering baculoviruses (DIs). Cell culture experiments with bacmid-derived baculoviruses showed that spontaneous deletions in the foreign bacterial artificial chromosome (BAC) sequences readily occurred. These deletions correlated with a low density of baculovirus homologous (repeat) regions (hrs), which are located dispersed throughout the baculovirus genome and are believed to act as origins of viral DNA replication (oris). To test the hypothesis that deletions are more likely to occur in regions with a low ori density, the properties of bacmid-derived baculoviruses with an additional hr in the unstable BAC sequences were compared to the standard bacmid-derived baculovirus in a continuous cascaded insect-cell bioreactor configuration. All viruses were equipped with a green fluorescent protein (GFP) gene and a gene encoding the classical swine fever virus E2 glycoprotein (CSFV-E2). The insertion of an extra hr in the BAC vector led to improved genetic stability of adjacent sequences, resulting in prolonged protein expression. The maintenance of the BAC sequences appeared to be dependent on the orientation of the inserted hr. The advantages of the utilization of hrs to improve the stability of baculovirus expression vectors for the large-scale protein production in insect-cell bioreactors are discussed. 相似文献
984.
We have investigated the usefulness of hypocotyl (cultured on N1B2 medium) and cotyledon explants (on CR medium: Murashige
and Skoog (MS) medium, 3% sucrose, 20 μm benzylaminopurine, pH 5.8) for the regeneration of shoots of the Korean radish ‘Jin
Ju Dae Pyong’. The importance of ethylene (indirectly), polyamines and gelling agent were studied in both media. Although
the addition of ethylene-inhibitors and silver nitrate to the culture media were beneficial towards shoot regeneration and
agar-based treatments (0.8% w/v) being superior in shoot production compared to agarose treatments (0.4% w/v), both explants
responded differently in culture. Hypocotyls cultured in the presence of silver nitrate or aminoethoxyvinylglycine (AVG) regenerated
significantly (p < 0.05) more shoots compared to N1B2 medium alone; supplementation of 20 μM AVG to N1B2 medium gave optimal shoot production
(40% of explants regenerating shoots). The addition of 10 μM AVG to CR medium produced maximum shoot regeneration from cotyledon
explants (60% producing shoots). Plants derived from 3-month-old cultures produced greater seed weights, larger leaves and
greater genetic variability (50–80% of cells having 20–40 chromosomes) compared to seed-derived (85–90% diploid) and plants
from 1-month-old cultures (78–88% diploid). Our results show, that if prolonged culture of explants is avoided, a large number
of phenotypically-normal plants can be produced, which in turn, could be utilized in the genetic improvement of radish. 相似文献
985.
The chromosome constitution of hybrids and chromatin patterns of Agropyron elongatum (Host)Neviski in F5 somatic hybrid lines -1–3 and I-1-9 between Triticum aestivum L. and A. elongatum were analyzed. Based on the statistic data
of pollen mother cells, F5 I-1-9 and-1-3 had 20–21 bivalents with a frequency of 84.66% and 85.28%, of which, 89.83% and 89.57% were ring bivalents.
The result indicated that both hybrid lines were basically stable in the chromosome constitution and behavior. RAPD analysis
showed that the two hybrids contained biparental and integrated DNA. GISH (Genome in situ hybridization) revealed that in
the form of small chromosome segments, A. elongatum chromatin was scattered on 4–6 wheat chromosomes near by the region of
centromere and telomere in the two hybrid lines. SSR analysis indicated that A. elongatum DNA segments were distributed on
the 2A, 5B, 6B and 2D wheat chromosomes in the hybrids, which was in accordance with the GISH results that small-segments
intercalated poly-site. 相似文献
986.
Stephanie Chhan Douglass H. Morse 《Ethology : formerly Zeitschrift fur Tierpsychologie》2019,125(7):457-464
Mated females of haplodiploid species can vary the sex ratio of their offspring, but virgin or sperm‐depleted females can produce only males. Depending on the costs and benefits, the theory of constrained sex allocation states that female haplodiploids may vary in their propensity to mate, with important implications for the populations’ sex ratio. Unmated female parasitoid wasps Alabagrus texanus (Braconidae) have been observed to reject matings with males, even under highly confined spatial conditions. We performed field trials to determine whether unmated female A. texanus would mate. We then compared the preferences of the resulting unmated (constrained) and mated (unconstrained) female wasps for shelters constructed and occupied by their hosts, fern moth caterpillars Herpetogramma theseusalis (Crambidae) on fern fronds. We presented the wasps with pairs of shelters collected from the field that differed in size, as well as freshness, fern species, and presence or absence of caterpillars. Unconstrained females searched small shelters more frequently than did constrained females and tended to favor senesced (old) shelters over fresher ones. They did not differ in choice between shelters on marsh and sensitive ferns or between shelters containing caterpillars and empty shelters. The preference for small shelters by the unconstrained wasps may enhance their rate of contacting favorable hosts, but the foraging regime of the constrained females should expose them to caterpillars at sites infrequently searched by the unconstrained females. 相似文献
987.
988.
Mitotic chromosome numbers and karyotypes of 13 South American species (12 native and one naturalized) from four sections of SOLANUM subgen. LEPTOSTEMONUM were studied. Chromosome numbers of S. ACERIFOLIUM, S. AENICTUM, S. CONDITUM, S. CONSIMILE, S. INCARCERATUM, and S. PLATENSE are reported for the first time. The number 2n = 24 was found in most species, while 2n = 22 was found in S. MAMMOSUM and S. PLATENSE. The latter is the second SOLANUM with this unusual number. Satellites are always present and were visible in more than 50 % of the cells studied. Karyotypes are symmetrical: M and SM chromosomes are common, whereas ST chromosomes are rare. The karyotypes of S. AENICTUM, S. MAMMOSUM, and S. PANICULATUM are comparatively asymmetrical. Species can be distinguished by a combination of chromosome number, karyotype formulae, karyotype length, the position of satellites in a particular chromosome pair, and asymmetry indices. The phenogram obtained does not reflect the sectional arrangements or the systematic affinities of the species studied. In sect. ACANTHOPHORA, increased asymmetry is associated with derived characters (strong andromonoecy, winged seeds, mammiform fruits). Diversification in the subgenus is suggested to be related to visible chromosome rearrangements and cumulative, cryptic structural changes may have also played a relevant evolutionary role. 相似文献
989.
Endothermic animals resident in hot, arid terrestrial environments are likely to face a trade‐off between their ability to obtain water and elevated thermoregulatory water requirements. We assessed whether daily water flux (DWF) is higher on hot days, reflecting increases in evaporative cooling demands, in an arid‐zone bird that obtains its water through food intake. We obtained measurements of DWF (partitioned into water influx and efflux rates) in 71 White‐browed Sparrow‐Weavers Plocepasser mahali at a desert site and a semi‐desert site, during summer in the Kalahari Desert of southern Africa. We found no evidence that DWF varied with maximum daily air temperature (Tair, range = 27.6–39.2 °C). Instead, DWF was lower during dry periods than in the wet season at the semi‐desert site. Furthermore, birds showed deficits in water balance (water influx/water efflux) during the dry periods at both sites. Our data show that DWF is low in a non‐drinking bird that obtains its water through food, and that demands for evaporative water loss on very hot days (maximum Tair of 40–44 °C) may exceed water intake rates during hot and dry periods. Species that do not have opportunities to drink will experience strong trade‐offs between thermoregulation, hydration state and activity levels as temperatures increase. 相似文献
990.
Exogenously supplied bovine haemin, fed to etiolated barley leaves, inhibited chlorophyll synthesis in leaves exposed to light. Haemin inhibited the regeneration of protochlorophyllide (P650) and the conversion of exogenously supplied δ-aminolaevulinate (ALA) to protochlorophyll (P630). The effect of haemin on chlorophyll production was overcome by incubating the leaves in water in the dark before light treatment, suggesting the operation of a rapid haem destruction mechanism in leaves. Protohaem turnover in dark-grown leaves was between 8 and 9 hr, based on the rate of degradation of erogenous haemin and the rate of protohaem breakdown in laevulinic acid (LA) treated leaves. The rate constant for haem destruction was 85 pmol/nmol/hr in the dark and 45 pmol/nmol/hr after 4 hr light. There was no evidence that light affects the synthesis of protohaem. It appears that the regulation of endogenous levels of protohaem is by breakdown and it is this mechanism which is under light control. Haem considerably decreased the incorporation of radioactivity from glycollate-[14C], glycine-[14C] and glutamate-[14C] into accumulated ALA in the presence of LA. 相似文献