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161.
The vertical distribution of Alexandrium tamarense/ catenella (hereinafter Alexandrium spp.) cysts was investigated with special attention to living cysts filled with fresh protoplasm and empty cysts. In addition, based on the incubation experiments of Alexandrium spp. cysts, the germination ability of the cysts was examined. A sediment core 63 cm in length, collected from Kure Bay of the Seto Inland Sea, West Japan, in September 2000, was provided for an analysis on the vertical distribution of Alexandrium spp. cysts. Samples from every 1 cm interval depth from the top down to 13 cm depth of the same core were taken to examine the germination ability of the cysts. Results show that Alexandrium spp. cysts were continuously observed from 59 to 60 cm depth to the top. The cyst densities in the upper parts of the core (from 9 to 10 cm depth to the top) were much more abundant those that in the lower parts (below 10–11 cm depth). The relationship between living and empty cysts in each depth did not reveal a positive correlation with the sediment depth. Based on the sedimentation rate of the core sediment (approximately 1.6 cm/year), Alexandrium spp. cysts have been produced since 1962, and a remarkable increase of these cysts was observed from ca 1993. Such a rapid increase of Alexandrium spp. cysts has probably been as a result of dense blooms of A. tamarense occurring since 1992 in Hiroshima Bay, including Kure Bay. The germination of Alexandrium spp. cysts was observed in samples collected from the top to 12–13 cm depth of the core. It suggests that the Alexandrium spp. cysts can keep the germination ability for more than 8 years. 相似文献
162.
Little is known about the mechanisms through which mother's cognitive ability operates in enhancing her children's health. This paper analyzes how maternal returns to cognitive ability on children's height reflect contemporaneous endowments and childhood background of the mother. Results suggest that maternal returns to cognitive ability on child height are less likely to reflect observed mother's childhood endowments as measured by parental transmission of knowledge or school quality, but are more likely to be associated with learning to be a mother, and with a better capacity to take advantage of household and community available resources. 相似文献
163.
烤烟主要性状配合力和相关性研究 总被引:3,自引:0,他引:3
选用7个烤烟品种作亲本,采用Griffing方法I,利用7×7完全双列杂交,对烤烟产量、产值、上等烟比例、均价和级指等主要经济性状配合力和相关性进行研究,结果表明:各农艺性状和经济性状的遗传特性同时受基因加性效应、非加性效应以及反交效应的共同作用.从经济性状来看,以红花大金元和云烟317作亲本之一,特别是红花大金元作母本配制的杂交组合优势较强.以净叶黄作为亲本之一配制的杂交组合没有优势,显示出各组合的产量、产值等经济性状较低. 相似文献
164.
刈割对紫花苜蓿根系生长影响的初步分析 总被引:27,自引:2,他引:25
研究了不同刈割次数对紫花苜蓿根系发育能力的影响。结果表明:刈割抑制紫花苜蓿主根的纵向(垂直)生长,而促进其横向(直径)生长,并使紫花苜蓿侧根发生总数减少和垂直分布的总体格局向表层集中,随着刈割次数的增加,侧根集中分布在土壤表层的比例也增加;刈割使根系生物量和体积总量减少,并随着刈割次数的增加,这种减少趋势更加明显,同时在土壤中的垂直分布变浅。 相似文献
165.
干旱胁迫下几种荒漠植物抗氧化能力的比较研究 总被引:32,自引:7,他引:25
对3种荒漠植物沙拐枣、梭梭和沙枣在干旱胁迫下的抗氧化能力进行了比较研究。结果表明,3种荒漠植物长期处于干旱生境下,都受到不同程度的膜脂过氧化,其中,沙枣的膜脂过氧化程度大于梭梭和沙拐枣。在1d的变化中,随着水势的下降,上午10:00前3种植物体内MDA含量都表现为上升趋势,此后梭梭和沙拐枣体内MDA含量表现为持续下降,到下午18:00达到最低,说明尽管水分胁迫在加强,它们却表现出极强的抗氧化胁迫能力;而沙枣体内MDA含量在下午18:00又开始上升,表明沙枣表现出一定的调节能力,但其能力有限,低于梭梭和沙拐枣。3种植物对干旱胁迫的应激方式不同;沙拐枣体内的SOD活性和ASA含量明显高于梭梭和沙枣,这与其体内相对较低的O2含量具有很好的一致性;对于植物体内H2O2的清除,抗氧化酶系统对沙拐枣体内的H2O2的清除起了一定的作用,但不是主要的,抗氧化剂GSH起主要作用,而梭梭体内南抗氧化酶系统中的CAT起主要作用,抗氧化剂起辅助作用;沙枣体内的AsA-POD起主要作用,其它的抗氧化酶和氧化剂起辅助作用。同时,植物体内还保持管各种酶的平衡。 相似文献
166.
The indole-3-pyruvate decarboxylase gene (ipdC), coding for a key enzyme of the indole-3-pyruvic acid pathway of IAA biosynthesis in Azospirillum brasilense SM was functionally disrupted in a site-specific manner. This disruption was brought about by group II intron-based Targetron
gene knock-out system as other conventional methods were unsuccessful in generating an IAA-attenuated mutant. Intron insertion
was targeted to position 568 on the sense strand of ipdC, resulting in the knock-out strain, SMIT568s10 which showed a significant (∼50%) decrease in the levels of indole-3-acetic
acid, indole-3-acetaldehyde and tryptophol compared to the wild type strain SM. In addition, a significant decrease in indole-3-pyruvate
decarboxylase enzyme activity by ∼50% was identified confirming a functional knock-out. Consequently, a reduction in the plant
growth promoting response of strain SMIT568s10 was observed in terms of root length and lateral root proliferation as well
as the total dry weight of the treated plants. Residual indole-3-pyruvate decarboxylase enzyme activity, and indole-3-acetic
acid, tryptophol and indole-3-acetaldehyde formed along with the plant growth promoting response by strain SMIT568s10 in comparison
with an untreated set suggest the presence of more than one copy of ipdC in the A. brasilense SM genome. 相似文献
167.
H. J. Barclay 《Population Ecology》2001,43(3):197-206
Models were constructed for control of a pest species by the release of sterile insects and these models explored the consequences
of incomplete sterility. This feature was then coupled with the lack of competitive ability of released insects, the immigration
of insects from outside the control area, and the mode of population regulation (density independent vs. density dependent).
Using the density-independent models, it was seen that the limits on residual fertility of treated insects become much more
stringent when incomplete sterilization is combined with a lack of competitive ability and immigration of insects into the
control area. Strong density dependence in the system has a marked moderating effect on the requirements for sterility, competitive
ability, and immigration. However, if the density-independent limits on these factors are exceeded, then suppression is possible,
but collapse of the pest population is impossible using sterile releases alone. Even suppression might not be satisfactory
if these three detrimental factors are prominent. It is suggested that one remedy is the use of the sterile release method
in combination with other control methods.
Received: January 18, 2001 / Accepted: August 7, 2001 相似文献
168.
端粒酶反义cDNA对乳腺癌细胞损伤修复能力的影响 总被引:3,自引:0,他引:3
利用反义核酸技术将端粒酶RNA的全长cDNA反向导入乳腺癌MCF 7细胞基因组中 .通过单细胞凝胶电泳实验发现 ,其DNA受H2 O2 损伤后的修复能力下降 .但端粒酶活性抑制为何引起其DNA损伤修复能力下降的原因尚待进一步研究 . 相似文献
169.
170.
Apparent decoupling of prey recognition ability with prey availability in an insular snake population 总被引:2,自引:0,他引:2
Numerous studies on the feeding behavior of snakes have reported the consistency of tongue-flick responses with their natural
diets. For representatives of widely distributed, dietary generalist species from particular localities, we can expect that
their tongue-flick responses to potential prey unavailable in their original habitats have been reduced whereas those to prey
common in the habitats have been enhanced. To test this hypothesis, intraspecific variation in tongue-flick responses to prey
chemicals was examined using ingestively naive snakes (Elaphe quadrivirgata) from dietarily different populations: populations from the main Japanese island, where the snakes' diet predominantly consists
of sympatric frogs, and from Mikura-jima Island, where no frogs occur and the snakes thus chiefly prey on lizards. We presented
chemical stimuli from six items including those from their natural and potential prey (fish, frog, lizard, mouse, water, and
cologne) to newborn snakes. Significant effects of stimuli on the tongue-flick responses were detected. On the other hand,
effects of population and interaction between stimuli and population were not significant, and individual comparisons revealed
no significant interlocality differences in responses to either frog or lizard chemicals. Thus, our hypothesis was not supported.
However, in the Mikura-jima sample, significantly fewer snakes responded to frog chemicals than in the main island sample.
The significance of the inconsistency between prey recognition ability and prey availability in the Mikura-jima population
are discussed.
Received: October 17, 2000 / Accepted: December 14, 2000 相似文献