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21.
鹅掌楸雌配子体败育对生殖的影响 总被引:12,自引:0,他引:12
胚珠和雌配子体败育是限制鹅掌楸生殖成功的一个重要因素。中国东部和西部鹅掌楸种群在雌配子体发育的各阶段上的败育程度有差异,以西部种群的发育较好。西部分布区较合适的生境促进了胚囊的发育,一定温度和湿度的环境可以活化珠心细胞输送营养物质供给雌配子体发育,提高受精和结籽的能力 相似文献
22.
Christian Biémont Cristina Vieira Christine Hoogland Géraldine Cizeron Catherine Lœvenbruck Claude Arnault Jean-Pierre Carante 《Genetica》1997,100(1-3):161-166
To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed
the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of
insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects
of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is
strengthened by the absence of the negative correlation between recombination rate and TE copy number along the chromosomes,
which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted
by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural
populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra,
Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1–2
× 10-3 whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations.
The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements
in this species could result from a low transposition rate.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
23.
Characterization of Calpain-Mediated Proteolysis of GluR1 Subunits of α-Amino-3-Hydroxy-5-Methylisoxazole-4-Propionate Receptors in Rat Brain 总被引:1,自引:0,他引:1
Xiaoning Bi Jing Chen Sandeeb Dang Robert J. Wenthold Georges Tocco Michel Baudry 《Journal of neurochemistry》1997,68(4):1484-1494
Abstract: Previous results have indicated that GluR1 subunits of α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors are targets of calpain. In the present study, we determined the effects of calpain treatment of synaptic membranes on GluR1 subunits using western blots with antibodies directed against the C-terminal (C-Ab) and the N-terminal (N-Ab) domains of the proteins, and compared them with the effects of calcium treatment of frozen-thawed brain sections. Calpain treatment of synaptic membranes resulted in a large decrease in the GluR1 band (105 kDa) labeled with C-Ab and in the formation of a doublet band labeled with N-Ab due to the appearance of a new species of GluR1 (98 kDa). These effects were blocked almost completely by calpain inhibitors. Calpain-induced changes in GluR1 immunological properties were not associated with modifications of [3 H]AMPA or 6-cyano-7-[3 H]nitroquinoxaline-2,3-dione ([3 H]CNQX) binding. Treatment of frozen-thawed brain sections with concentrations of calcium as low as 0.2 m M resulted in a large decrease in the 105-kDa GluR1 band and in the concurrent appearance of the 98-kDa band. This treatment was associated with increased [3 H]AMPA and [3 H]CNQX binding. These results suggest that there exist several types/states of GluR1 subunits exhibiting different sensitivities to calpain. Our data also indicate the existence of additional calcium-dependent processes regulating the characteristics of receptors in intact tissues. 相似文献
24.
这是在我国首次发现的鲎类足迹化石,标本采自安徽南陵下三叠统青龙组薄层灰岩。除对它们的形态特征加以描述、分析和比较外,还就其形成环境及保存特点作了初步的探讨。 相似文献
25.
牛生长激素基因在马铃薯中的表达 总被引:5,自引:0,他引:5
将牛生长激素基因cDNA 与Patatin ClassI启动子及NOS3终止子连接,构建了表达载体pPBGT. 用直接法将表达载体转入农杆菌(Agrobacterium tum efaciens) LBA4404(pRAL4404)菌株, 用此菌株转化马铃薯(Solanum tuberosum )得到再生植株. 经NPTⅡ活性检测,总DNA PCR和Southern blot证明目的基因已整合到马铃薯基因组中.RNA 点杂交和Western blot表明牛生长激素基因已在转基因马铃薯块茎中转录和表达 相似文献
26.
27.
1 前言 土地处理系统对悬浮固体具有很好的净化效果,其净化率要害99%以上,但实际过程中,一些干扰 相似文献
28.
Seventeen highly-inbred lines of Drosophila melanogaster extracted from an M' strain (in the P/M system of hybrid dysgenesis) were studied for their cytotype and the number and chromosomal location of complete and defective P elements. While most lines were of M cytotype, three presented a P cytotype (the condition that represses P-element activity) and one was intermediate between M and P. All lines were found to possess KP elements and only eight to bear full-sized P elements. Only the lines with full-sized P elements showed detectable changes in their P-insertion pattern over generations; their rates of gain and of loss of P-element sites were equal to 0.12 and 0.09 per genome, per generation, respectively. There was no correlation between these two rates within lines, suggesting independent transpositions and excisions in the inbred genomes. The results of both Southern blot analysis and in situ hybridization of probes made from left and right sides of the P element strongly suggested the presence of a putative complete P element in region 1A of the X chromosome in the three lines with a P cytotype; the absence of P copy in this 1A region in lines with an M cytotype, favours the hypothesis that the P element inserted in 1A could play a major role in the P-cytotype determination. Insertion of a defective 2 kb P element was also observed in region 93F in 9 of the 13 M lines. The regulation of the P-element copy number in our lines appeared not to be associated with the ratio of full-length and defective P elements. 相似文献
29.
In Escherichia coli, distinct but similar minicell phenotypes resulting from mutation at the minB locus and increased expression of ftsZ suggested a possible interaction between these genes. A four- to fivefold increase in FtsZ resulting from increased gene dosage was found to suppress the lethality of minCD expressed from the lac promoter. Since increased MinCD did not affect the level of FtsZ, this suggested that MinCD may antagonize FtsZ to inhibit its cell division activity. This possibility was supported by the finding that alleles of ftsZ isolated as resistant to the cell division inhibitor SulA were also resistant to MinCD. Among the ftsZ(Rsa) alleles, two appeared to be completely resistant to MinCD as demonstrated by the lack of an effect of MinCD on cell length and a minicell phenotype observed in the absence of a significant increase in FtsZ. It was shown that SulA inhibits cell division independently of MinCD. 相似文献
30.
When cultured individually, isolated inner cell masses (ICMs) of the mouse blastocyst form an outer layer of endoderm and remain in suspension as spherical structures for several days. Conditioned media from certain teratocarcinoma- and blastocyst-derived cell lines contain one or more outgrowth promoting factors (OPF) which facilitate attachment and outgrowth of ICMs, in some cases prior to endoderm formation. OPF adheres to culture dishes and presumably promotes ICM cell outgrowth by alteration of the substratum. Analyses indicate that the active material is a nondialyzable protein which is stable to freezing and thawing, a wide range of pH, and extended incubation at 37°C. However, inactivation takes place at 60°C for 20 min. Although these properties of OPF are in some ways similar to those of various proteins which have been implicated in cell adhesion and spreading, differences between OPF and most of these other proteins are evident. The detection of OPF activity in conditioned medium from primary cultures of embryonic and some extraembryonic cell types suggests that the factor is biologically significant, perhaps, for example, in the spreading of parietal endoderm cells along the surface of the trophoblast layer. 相似文献