排序方式: 共有24条查询结果,搜索用时 15 毫秒
1.
2.
采用“定期起苗”法,从6 月10 日—8 月30 日止,分别统计从越冬块茎上萌发出的再生苗及其后代蔓生枝系再生苗的数量,从而得出扁秆藨草再生苗各旬株数增长的指数方程;又用“定株观察”法,对12 株越冬块茎上的再生苗及其全部后代植株开花、结实数量进行统计,探讨扁秆藨草有性繁殖的能力,然后进行综合计算,求得扁秆藨草种群的内禀增长率r=7.24,阐明了扁秆藨草很高的内禀增长率是其种群过度生长的根本原因;通过对其过度生长关键时刻的判断,选择灭草的关键期,有效地灭杀此种恶性杂草 相似文献
3.
《Journal of receptor and signal transduction research》2013,33(1):99-109
AbstractMammalian D1 and D2 dopamine receptors were stably expressed in Drosophila Schneider‐2 (S2) cells and screened for their pharmacological properties. Saturable, dose‐dependent, high affinity binding of the D1‐selective antagonist [3H]SCH‐23390 was detected only in membranes from S2 cells induced to express rat dopamine D1 receptors, while saturable, dose‐dependent, high affinity binding of the D2‐selective antagonist [3H]methylspiperone was detected only in membranes from S2 cells induced to express rat dopamine D2 receptors. No specific binding of either radioligand could be detected in membranes isolated from uninduced or untransfected S2 cells. Both dopamine D1 and D2 receptor subtypes displayed the appropriate stereoselective binding of enantiomers of the nonselective antagonist butaclamol. Each receptor subtype also displayed the appropriate agonist stereoselectivities. The dopamine D1 receptor bound the (+)‐enantiomer of the D1‐selective agonist SKF38393 with higher affinity than the (?)‐enantiomer, while the dopamine D2 receptor bound the (?)‐enantiomer of the D2‐selective agonist norpropylapomorphine with higher affinity than the (+)‐enantiomer. At both receptor subtypes, dopamine binding was best characterized as occurring to a single low affinity site. In addition, the low affinity dopamine binding was also found to be insensitive to GTPγS and magnesium ions. Overall, the pharmacological profiles of mammalian dopamine D1 and D2 receptors expressed in Drosophila S2 cells is comparable to those observed for these same receptors when they are expressed in mammalian cell lines. A notable distinction is that there is no evidence for the coupling of insect G proteins to mammalian dopamine receptors. These results suggest that the S2 cell insect G system may provide a convenient source of pharmacologically active mammalian D1 and D2 dopamine receptors free of promiscuous G protein contaminants. 相似文献
4.
Most expression systems used for the over production of many enzymes employ carbon catabolite repressible promoters and hence must use sugar free, rich complex media. Use of expression systems to overcome carbon repression opens an avenue for exploiting cheap carbon sources for the production of recombinant enzymes. A self-inducible, catabolite repression free and above all a glucose-activated expression system has been developed using an industrially suitable thermophilic alpha-amylase as a model. The alpha-amylase gene of Bacillus licheniformis MSG without the 5' cre operator produced unimpeded glucose-enhanced expression when fused to the phosphate starvation-inducible strong pst promoter with optimum translation signals in a protease deficient Bacillus subtilis. A combination of high glucose with limited phosphate permitted sufficient biomass and fast transition to quiescent phase by phosphate starvation permitting 1250-fold induction for 70 h. A ~300-fold high productivity (9070 U mL-1) and 131-fold increase in specific expression in 2% glucose and a 100-fold high yield in 4% molasses were obtained compared to the production by the parent strain. The yield was 18.5-fold higher than that from the native promoter in an isogenic clone. This strategy of catabolite enhanced enzyme expression uncoupled from biomass formation can be applied for cost effective high production of proteins using starch or molasses. 相似文献
5.
高产铁载体荧光假单胞菌Pseudomonas fluorescens sp-f的筛选鉴定及其铁载体特性研究 总被引:9,自引:0,他引:9
采用改进的CAS检测平板从东湖中筛选得到了一株高产铁载体细菌sp-f,并用CAS检测液定量检测其分泌铁载体量,发现其As/Ar仅0.09(OD680),Su(Siderophore Unit)为90%,达到产铁载体菌最高级。用BIOLOG检测板,结合细菌生理生化反应、形态观察和16S rDNA序列比对分析等分类鉴定方法,确定sp-f为一株荧光假单胞菌。P.fluorescenssp-f生长过程中胞外铁载体的量在对数生长前期累积达到最高后有所减少,至稳定期时菌液中铁载体量达到稳定。在已知铁载体特异吸收峰波长下,用反向高效液相色谱检测无铁环境和高铁环境下培养液上清,比较发现sp-f上清含有3种含儿茶酚胺类基团铁载体,其中包括荧光和非荧光性的脓菌素,200μmol/L Fe2 可完全抑制荧光性质脓菌素的分泌,但非荧光脓菌素的分泌不受抑制,并且对非脓菌素的儿茶酚胺类铁载体的合成分泌反而具有一定的诱导作用。 相似文献
6.
采用碱液吸收法对内蒙古锡林河流域羊草 (L eymus chinensis)草原群落土壤呼吸速率进行了连续 2年的野外测定 ,并通过多元回归手段对其影响因子进行了分析。结果表明 :1) 1998~ 1999年两个生长季羊草群落土壤呼吸速率的季节动态均为单峰型曲线 ,最大值出现在 7月下旬 ;2 ) CO2 释放速率、气温和土壤含水量之间有如下关系 :L n Res=5 .85 96 0 .0 12 5 M 0 .0 394T 0 .0 0 49M× T,R2 =0 .70 96 ,表明约有 70 %的土壤呼吸量变化是由气温和土壤含水量共同决定的 ,其中以温度为主 (Res=2 5 6 .75 T0 .6 5 5 7,R2 =0 .5 779) ,Q1 0 在 2 .0~ 3.0之间 ;3)羊草无放牧群落生长季的土壤呼吸总量在 2 49.4~ 32 0 .7g C.m- 2 .a- 1之间 ,放牧群落在 2 37.0~ 30 5 .6 g C.m- 2 .a- 1之间 ,放牧对土壤呼吸影响不大。 相似文献
7.
Mlh1-Mlh3, a Meiotic Crossover and DNA Mismatch Repair Factor,Is a Msh2-Msh3-stimulated Endonuclease
Maria V. Rogacheva Carol M. Manhart Cheng Chen Alba Guarne Jennifer Surtees Eric Alani 《The Journal of biological chemistry》2014,289(9):5664-5673
Crossing over between homologous chromosomes is initiated in meiotic prophase in most sexually reproducing organisms by the appearance of programmed double strand breaks throughout the genome. In Saccharomyces cerevisiae the double-strand breaks are resected to form three prime single-strand tails that primarily invade complementary sequences in unbroken homologs. These invasion intermediates are converted into double Holliday junctions and then resolved into crossovers that facilitate homolog segregation during Meiosis I. Work in yeast suggests that Msh4-Msh5 stabilizes invasion intermediates and double Holliday junctions, which are resolved into crossovers in steps requiring Sgs1 helicase, Exo1, and a putative endonuclease activity encoded by the DNA mismatch repair factor Mlh1-Mlh3. We purified Mlh1-Mlh3 and showed that it is a metal-dependent and Msh2-Msh3-stimulated endonuclease that makes single-strand breaks in supercoiled DNA. These observations support a direct role for an Mlh1-Mlh3 endonuclease activity in resolving recombination intermediates and in DNA mismatch repair. 相似文献
8.
9.
Trees, perennial phanerophytes, display a rich variety of rhythmic phenomena. These are either due to exclusive environmental
entrainment or due to the functioning of endogenous oscillators independent of the environment. Both types of rhythms are
covered in this review. Purely environment controlled rhythms may be considered as a prelude to endogenous rhythms. Environment
controlled rhythms discussed are (i) the diurnal rhythms of nyctinastic and heliotropic leaf movements and oscillatory phenomena
of photosynthesis, such as the midday depression and Crassulacean acid metabolism (CAM), and (ii) the annual rhythms of annual
growth ring formation, autumnal leaf senescence, over wintering mechanisms and flowering. Among the diurnal rhythms, nyctinastic
movements and CAM are also free-running endogenous rhythms showing the operation of circadian clocks in trees. In leaf senescence,
over wintering, and flowering control, photoperiod sensing is involved which suggests the participation of endogenous clocks.
A question asked is if diurnal and annual rhythms are mechanistically correlated. Evidently, phenological phenomena based
on photoperiodism (as dependent on measurement of night length) are co-ordinately regulated by the phytochrome system and
the circadian clocks and many aspects of annual developments and over wintering are linked to photoperiodism. The existence
in trees of circadian clock genes as known to be anchored in the genome of A. thaliana can be assessed by attempts of alignment with the sequenced genome of Populus or by isolating cDNA clones from trees to check them against the genome of A. thaliana. At extreme latitudes near the equator and north of the polar circle trees also display photoperiod-independent phenological
phenomena. In the polar region, total irradiance of red and far red light could possibly be involved and the signalling pathway
then involves phytochrome, and thus, may still be similar to that of photoperiodism. At the equator, total daily light irradiance
received or sensing the dynamics of daily changes in solar irradiance are essential and it remains enigmatic whether signalling
cascades are either attached to the circadian clocks in a still unknown way or totally independent of circadian clocks. 相似文献
10.
重组质粒pPIC9K-oLHαhCGβCTP的构建及在毕赤酵母中的表达 总被引:3,自引:0,他引:3
将人绒毛膜促性腺激素β-亚基的羧基肽(CTP)与羊黄体生成素(oLH)的α-亚基融合,通过设计两对引物,用部分重叠聚合酶链式反应(overlappingPCR)的方法构建了羊的α亚基CTP嵌合体.这个嵌合体被克隆到pPIC9K质粒中,用电打孔方法转入巴氏毕赤酵母(Pichiapastoris),并获高效表达.表达蛋白经SDS-PAGE和Western印迹证明分子量约为28kD.2.5L发酵罐大量培养,产量可达2.0g/L. 相似文献