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1.
Effects of adding different concentrations of melatonin (10?7, 10?9 and 10?11 M) to maturation (Experiment 1; Control, IVM  + 10?7, IVM  + 10?9, IVM  + 10?11) and culture media (Experiment 2; Control, IVC  + 10?7, IVC  + 10?9, IVC  + 10?11) were evaluated on in vitro bovine embryonic development. The optimal concentration of melatonin (10?9 M) from Experiments 1–2 was tested in both maturation and/or culture media of Experiment 3 (Control, IVM  + 10?9, IVC  + 10?9, IVM /IVC  + 10?9). In Experiment 1, maturated oocytes from Control and IVM  + 10?9 treatments showed increased glutathione content, mitochondrial membrane potential and percentage of Grade I blastocysts (40.6% and 43%, respectively). In Experiment 2, an increase in the percentage of Grade I blastocysts was detected in IVC  + 10?7 (43.5%; 56.7%) and IVC  + 10?9 (47.4%; 57.4%). Moreover, a lower number and percentage of apoptotic cells in blastocysts were observed in the IVC  + 10?9 group compared to Control (3.8 ± 0.6; 3.6% versus 6.1 ± 0.6; 5.3%). In Experiment 3, the IVC  + 10?9 treatment increased percentage of Grade I blastocysts with a lower number of apoptotic cells compared to IVM /IVC  + 10?9 group (52.6%; 3.0 ± 0.5 versus 46.0%; 5.4 ± 1.0). The IVC  + 10?9 treatment also had a higher mRNA expression of antioxidant gene (SOD 2) compared to the Control, as well as the heat shock protein (HSPB 1) compared to the IVM  + 10?9. Reactive oxygen species production was greater in the IVM /IVC  + 10?9 treatment group. In conclusion, the 10?9 M concentration of melatonin and the in vitro production phase in which it is used directly affected embryonic development and quality.  相似文献   
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Eight herbicide combinations containing imazapyr alone or in mixture with glyphosate, triclopyr, or picloram+2,4-D were applied July–August 1991 at each of three upland sites in the southeastern U.S., with or without a subsequent broadcast burn in September. Seedlings of loblolly (Pinus taeda L.) or slash (P. elliottii Engelm. var. elliottii) pine were planted that winter. Second-year (August 1993) vegetation responses indicate that broadcast burning, in combination with herbicides, was associated with increased abundances of grasses, forbs, and shrubs and decreased abundances of vines and hardwood trees. In the presence of burning, imazapyr-in-mixture treatments were associated with a high abundance of grass (53% cover) and a mean size of pines less than that of seedlings growing in imazapyr-alone treatments. In the absence of burning, imazapyr-alone treatments were associated with a high abundance of blackberry (21% cover), an average height of hardwoods (131 cm) exceeding that of pines (71 cm), and a mean size of pines less than that of trees growing in imazapyr-in-mixture treatments. Hardwood height in the absence of burning was less when imazapyr was combined with glyphosate (75 cm) than with triclopyr (102 cm). Regardless of the presence or absence of burning, size of pines and abundance of shrubs and hardwoods did not differ between imazapyr rates of 0.56 and 0.84 kg acid equivalent/ha or among herbicides applied in mixture with imazapyr.  相似文献   
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Three cutting heights, 2±5, 7±6 and 12±7 cm (1, 2±5 and 5 in.) and three levels of fertilizer N, 168, 280 and 392 kg N/ha (150, 250 and 350 Ib N/ac) were imposed on a sward of Italian ryegrass (Lolium multiflorum) cv. Irish. Lowering the cutting height and increasing the level of applied N increased the yield of herhage DM. Increasing the level of applied N had a greater effect on the chemical composition of the herbage than altering the cutting height  相似文献   
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Advances in understanding insecticide resistance in the peach-potato aphid, Myzus persicae (Sulzer), at the genotypic, biochemical and molecular levels have led to rapid and precise methods for the detection of several resistance mechanisms (elevated carboxylesterase, modified acetylcholinesterase or MACE, and knockdown resistance or kdr) in individual insects, and for monitoring their frequencies over space and time. This paper summarises the results of two long-term surveys of resistance dynamics in M persicae in England, based on samples collected directly from field and glasshouse crops or from four 12.2-m suction traps. The study showed marked fluctuations in resistance frequencies that probably reflect the counteracting forces of selection imposed by insecticides for aphids possessing more copies of esterase resistance genes, and selection against these forms when insecticide use is relaxed. There is growing evidence that several different resistance mechanisms in M persicae have associated fitness costs. In the case of esterase and MACE, these costs are apparently strong enough to effect a decline in resistance frequency over winter, and a more prolonged decline over successive cropping seasons when aphid numbers are insufficient to trigger intensive chemical applications. Changes in the overall frequency of resistance genotypes may also be influenced by the predominance of year-round parthenogenesis in M persicae in the UK, leading to non-random associations between mechanisms and selection operating on clonal lineages rather than individual genotypes.  相似文献   
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ABSTRACT The abundance of Verticillium dahliae in the soil and the incidence of V. dahliae-infected plants were determined for 12 commercial processing tomato fields in Kent County, Ontario. Comparison of the data with those from a previous survey of fields in adjacent Essex County showed that soil inoculum levels and incidence of infection were generally lower in Kent County fields and that race 2 V. dahliae was not common in Kent County. From the two counties, 128 isolates were characterized by restriction fragment length polymorphism (RFLP) analysis, using the subspecies-specific repetitive DNA sequence E18. A subset of these isolates was also characterized by vegetative compatibility and DNA hybridization analysis with a second subspecies-specific DNA sequence. Isolates with E18 RFLP profiles highly similar to those of isolates previously collected from potato fields in North America were prevalent in Essex County tomato fields but not common in Kent County fields. The data are consistent with the hypothesis that the group I isolates were introduced into southwestern Ontario with potato and that the different cultural practices in Essex County and Kent County have contributed to the differences in the accumulation of these isolates in the two regions.  相似文献   
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