排序方式: 共有41条查询结果,搜索用时 31 毫秒
1.
KAZUYUKI MIKAMI 《Development, growth & differentiation》1985,27(1):21-27
It has been known that, immediately after the third division of fertilization nucleus (synkaryon), nuclei localized near the posterior region of exconjugant are to be macronuclear anlagen and those near the anterior region are to be presumptive micronuclei in Paramecium caudatum. One of such posterior nuclei was transplanted into amicronucleate cell at vegetative phase in this work. The implanted nuclei were able to divide at every fission. Their DNA content was nearly equal to or less than ordinary micronuclei during vegetative phase. When conjugation was induced between clones obtained and amicronucleates, macronuclear anlagen developed from the division products of implanted nuclei and thereafter derivative caryonides were true to the marker gene of implanted nuclei. The results indicate that there was no intrinsic difference between nuclei localized anteriorly and those situated posteriorly in exconjugant. Differentiation of nuclei into macronucleus may be irreversible at the stage of anteroposterior localization of the nuclei. The role of nuclear division in differentiation may be only to transport the daughter nuclei into the cytoplasm/cortex differentiated anteroposteriorly. 相似文献
2.
A high temperature treatment at 35? for 5 days followed by alow temperature treatment at 0-5? for 25 days was given at fifteen-dayintervals to five groups each of two varieties (White Gold andCardinal Prince) stored in a storage room from September 27to November 26. The temperature treatment was apparently effectivefor sprouting of corms of both varieties at earlier period,but rather inhibitory at later period of dormancy. The plants of two varieties (Early Red and Spot Light) grownunder short day-length (9 hr) showed slightly earlier floweringand corm-forming than those grown under natural long day-length.These plants were harvested from July 1 to Septmber 1 at twentydayintervals, and sprouting of their corms with and without temperaturetreatment similar to the previous method was investigated. SpotLight corms did not sprout irrespective of temperature treatment.Early Red corms always sprouted earlier in the temperature-treatedlots, whereas they sprouted a little later in the non-treatedlots. The temperature treated corms grown under the short day-lengthshowed delaying and low percentage of sprouting. On the contrary,in the non-treated lots, sprouting of corms grown under thelong day-length was slower than those grown under the shortday-length.
1Contribution No. 24 from Laboratory of Horticulture (Olericultureand Floriculture), Kyoto University. (Received May 23, 1960; ) 相似文献
3.
KAZUYUKI MIKAMI 《The Journal of eukaryotic microbiology》1996,43(1):43-48
ABSTRACT. The germinal micronucleus divides six times during conjugation of Paramecium caudatum : this includes two meiotic divisions and one mitosis of haploid nuclei during mating, and three mitoses of a fertilization nucleus (synkaryon). Microsurgical removal of the macronucleus showed that micronuclei were able to divide repeatedly in the absence of the macronucleus, after metaphase of meiosis I of the micronucleus and also after synkaryon formation. When the macronucleus was removed after the first division of synkaryon, in an extreme case the synkaryon divided five times and produced 32 nuclei, compared to three divisions and eight nuclei produced in the presence of the macronucleus. Treatment with actinomycin D (100 μ /ml) inhibited the morphological changes of the macronucleus during conjugation and induced a multimicronucleate state in exconjugants. However, in other cells, it induced production of a few giant micronuclei. We conclude that the micronucleus is able to undergo repeated divisions at any stage of conjugation in the absence of the macronucleus once the factor(s) for induction of the micronuclear division has been produced by the macronucleus. The macronucleus may also produce a regulatory factor required to stop micronucler division. 相似文献
4.
Agricultural fields are an important anthropogenic source of atmospheric nitrous oxide (N2O) and nitric oxide (NO). Although many field studies have tested the effectiveness of possible mitigation options on N2O and NO emissions, the effectiveness of each option varies across sites due to environmental factors and field management. To combine these results and evaluate the overall effectiveness of enhanced‐efficiency fertilizers [i.e., nitrification inhibitors (NIs), polymer‐coated fertilizers (PCFs), and urease inhibitors (UIs)] on N2O and NO emissions, we performed a meta‐analysis using field experiment data (113 datasets from 35 studies) published in peer‐reviewed journals through 2008. The results indicated that NIs significantly reduced N2O emissions (mean: ?38%, 95% confidential interval: ?44% to ?31%) compared with those of conventional fertilizers. PCFs also significantly reduced N2O emissions (?35%, ?58% to ?14%), whereas UIs were not effective in reducing N2O. NIs and PCFs also significantly reduced NO (?46%, ?65% to ?35%; ?40%, ?76% to ?10%, respectively). The effectiveness of NIs was relatively consistent across the various types of inhibitors and land uses. However, the effect of PCFs showed contrasting results across soil and land‐use type: they were significantly effective for imperfectly drained Gleysol grassland (?77%, ?88% to ?58%), but were ineffective for well‐drained Andosol upland fields. Because available data for PCFs were dominated by certain regions and soil types, additional data are needed to evaluate their effectiveness more reliably. NIs were effective in reducing N2O emission from both chemical and organic fertilizers. Moreover, the consistent effect of NIs indicates that they are potent mitigation options for N2O and NO emissions. 相似文献
5.
6.
7.
8.
YUNSHENG LOU KAZUYUKI INUBUSHI TAKAYUKI MIZUNO TOSHIHIRO HASEGAWA YANHUNG LIN HIDEMITSU SAKAI WEIGUO CHENG KAZUHIKO KOBAYASHI 《Global Change Biology》2008,14(11):2678-2687
A pot experiment was conducted to investigate CH4 emissions from a sandy paddy soil as influenced by rice cultivars and atmospheric CO2 elevation. The experiment with two CO2 levels, 370 μL L−1 (ambient) and 570 μL L−1 (elevated), was performed in a climatron, located at the National Institute for Agro‐Environmental Sciences, Tsukuba, Japan. Four rice cultivars were tested in this experiment, including IR65598, IR72, Dular and Koshihikari. Tiller number, root length and grain yield were clearly larger under elevated CO2 than under ambient CO2. IR72 and Dular showed significantly higher tiller number, root length and grain yield than Koshihikari and IR65598. Average daily CH4 fluxes under elevated CO2 were significantly larger by 10.9–23.8% than those under ambient CO2, and varied with the cultivars in the sequence Dular ≧ IR72>IR65598 ≧ Koshihikari. Dissolved organic C (DOC) content in the soil was obviously higher under elevated CO2 than under ambient CO2 and differed among the cultivars, in the sequence IR72>Dular>Koshihikari>IR65598. The differences in average daily CH4 fluxes between CO2 levels and among the cultivars were related to different root exudation as DOC content, root length and tiller number. This study indicated that Koshihikari should be a potential cultivar for mitigating CH4 emission and simultaneously keeping stable grain yield, because this cultivar emitted lowest CH4 emission and produced medium grain yield. 相似文献
9.
10.
Fertilizer N use in Japan has decreased by about 30% from 1960 to 2000, while keeping a little increase in cereal yields. This has resulted in a significant increase in apparent nitrogen use efficiency, in particular for rice. On the other hand, national N load on the environment associated with the production and consumption of domestic and imported agricultural products has almost tripled during this period, mainly due to the dramatic increase of imports of food and feedstuffs. The environmental problems, including water and air pollution, caused by the excessive loads of N are serious public concerns and there is an urgent need to minimize N losses from agricultural production. In order to meet the necessity for reducing the environmental impacts by excess N, political and technological measures have been taken at regional and country levels. In recent years, the Japanese government has embarked on a series of policies to encourage transition to an environmentally conscious agriculture. Promoting proper material circulation with reducing fertilizer impact and utilizing biomass and livestock wastes is emphasized in these policies. The effectiveness of environmental assessment and planning for reducing regional and national N load has been discussed. Implementation of environmentally friendly technologies and management, both conventional and innovational, have been developed and adopted in Japanese agriculture. The effectiveness of conventional technologies in reducing environmental reactive N has been re-evaluated. Innovative technologies, such as use of controlled availability fertilizers and livestock wastes compost pellets, are being investigated and extended. A comprehensive approach that applies political and technological measures with closer cooperation is necessary to control reactive N in the environment. 相似文献