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431.
432.
Achim Bell Leonhard Kittler Günter Lber Christoph Zimmer 《Journal of molecular recognition : JMR》1997,10(6):245-255
We present titrations of the human δβ-globin gene region with DNA minor groove binders netropsin, bisnetropsin, distamycin, chromomycin and four bis-quaternary ammonium compounds in the presence of calf thymus topoisomerase II and DNase I. With increasing ligand concentration, stimulation and inhibition of enzyme activity were detected and quantitatively evaluated. Additionally we show a second type of stimulation, the appearance of strong new topoisomerase II cleavage sites at high ligand concentrations. The specific binding sites of the minor groove binders of the DNA sequence and their microscopic binding constants were determined from DNase I footprints. A binding mechanism for minor groove binders is proposed in order to explain these results especially when ligand concentration is increased. © 1998 John Wiley & Sons, Ltd. 相似文献
433.
Literature reports on the optical purity of the minor alkaloids in tobacco leaf and its products often contradict one another. The enantiomeric compositions of nornicotine, anatabine, and anabasine were measured using gas chromatography/mass spectrometry (GC/MS) (with a chiral stationary phase) in three types of tobacco leaf (Burley, Turkish, and Virginia); three types of smokeless tobacco (loose‐leaf, dry snuff, and moist snuff); and four types of cigarettes. Regardless of the tobacco type or product, anabasine always had the highest relative percentage of the minor (R)‐(+)‐enantiomeric component (between 40 and 46% vs. 54–60% of the (S)‐(−)‐enantiomer). Of the four common tobacco alkaloids, nicotine seems to have the highest enantiomeric excess (e.e.) while anabasine has the lowest (in the tobacco leaf and tobacco products analyzed). Nornicotine and anatabine have intermediate e.e. values. Chirality 11:82–84, 1999. © 1999 Wiley‐Liss, Inc. 相似文献
434.
The effects of phosphorus supply on the outcome of interactions between the hemiparasitic angiosperm Rhinanthus minor L. with its host species Lolium perenne L. were investigated in a glasshouse experiment. Host plants were grown in 3-l pots in the presence and absence of R. minor at limiting (0.13 mm P) and optimal (0.65 mm P) concentrations of phosphorus for the growth of the host species. Phosphorus was supplied at 2-day intervals in the form
of half-strength Long Ashton nitrate-based solution with phosphorus concentrations adjusted accordingly. Parasitism by R. minor significantly suppressed host growth, with final biomass losses ranging between 32% and 44%. Phosphorus supply had a marked
impact on the outcome of the host-parasite interaction. By the end of the growing period, parasite biomass at 0.65 mm P was 90% lower than that achieved at 0.13 mm P. In contrast, host biomass at 0.65 mm P was 74% higher than achieved at 0.13 mm P, indicting that the negative impact of parasitism on the host species was reduced when phosphorus supply was increased.
The effects of phosphorus on the host-parasite association appeared to be mediated by changes in both the morphological characteristics
of the host roots and the relative sink strengths of the host and parasite.
Received: 29 May 1999 / Accepted: 20 December 1999 相似文献
435.
The uranyl(VI)-mediated photocleavage of a Drew–Dickerson sequence oligonucleotide (5′-dGATCACGCGAATTCGCGT) either as the (self-complementary) duplex or cloned into the BamH1 site of pUC19 has been studied. At pH 6.5 in acetate buffer relatively enhanced photocleavage is observed at the 3′-end of the AATT sequence corresponding to maximum cleavage across the minor groove in the A/T tract. Thus maximum cleavage correlates with minimum minor groove width in the crystal structure and also with the largest electronegative potential according to computations. Using plasmid constructs with cloned inserts of the type [CGCG(A/T4)]n, we also analysed all possible sequence combinations of the (A/T)4 tract and in all cases we observed maximum uranyl-mediated photocleavage across the minor groove in the (A/T)4 tract without any significant differences between the various sequences. From these results we infer that DNA double helices of all (A/T)4 sequences share the same narrow minor groove helix conformation. 相似文献
436.
437.
Randerath's procedure for 32P postlabeling of 3'-monophosphate deoxyribonucleotides from digests of cellular DNA has been modified. 3'-Monophosphate deoxyribonucleotides are converted to 3',5'-bis[32P]phosphate deoxyribonucleotides with polynucleotide kinase and [32P]ATP; these products are enzymatically converted by P1 nuclease and polynucleotide kinase into 5'-[32P]monophosphate deoxyribonucleotides, which are separated from [32P]ATP on an anion-exchange column eluted with 0.1 M NaH2PO4, pH 6.5. Labeled mononucleotides in the effluent are separated by high-performance liquid chromatography. Values for the base composition of calf thymus DNA determined with this modified assay compare very favorably with reported values. The assay was used to measure the level of incorporation of the clinically useful agent bromodeoxyuridine into the DNA of 9L rat brain tumor cells. The modified assay appears to be a very accurate method for the determination of levels of base analogs incorporated into DNA. 相似文献
438.
Plasmatubules are tubular evaginations of the plasmalemma. They have previously been found at sites where high solute flux between apoplast and symplast occurs for a short period and where wall proliferations of the transfer cell type have not been developed (Harris et al. 1982, Planta 156, 461–465). In this paper we describe the distribution of plasmatubules in transfer cells of the leaf minor veins of Pisum sativum L. Transfer cells are found in these veins associated both with phloem sieve elements and with xylem vessels. Plasmatubules were found, in both types of transfer cell and it is suggested that the specific distribution of the plasmatubules may reflect further membrane amplification within the transfer cell for uptake of solute from apoplast into symplast. 相似文献
439.
Photoassimilating mature leaves of Cucumis melo exported carbon at a rate of 1.7 mg C·dm-2·h-1. Radiolabeling with 14C showed that stachyose and raffinose are the main carbohydrates translocated. Autoradiograms indicated that sieve elements of the abaxial phloem of minor veins are the sole conduits for carbon export from mature leaves and carbon import into immature leaflets. Sieve elements of the abaxial phloem are associated with intermediary cells which are intimately connected with the surrounding mesophyll cells by numerous plasmodesmata. Photoassimilate, labeled with 14C, was released into the leaf apoplast and could be trapped in a buffer solution circulating over the abraded adaxial epidermis. Carbon efflux was 1% of the carbon-export rate. A comparable distribution of 14C among the sugars, amino acids and organic acids, recovered from the free space and from leaf extracts, was recorded. The composition of released 14C-labeled carbohydrates in the free space resembled the pattern of photoassimilate, but differed clearly from the translocate. Release of organic compounds into the leaf apoplast was stimulated by chelating agents like Na-ATP, ethylenediaminetetraacetic acid and ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid; a correlation between carbon efflux into the apoplast and carbon export from the leaf was not detected. It is suggested that the release of organic compounds into the leaf apoplast of Cucumis melo is the consequence of a general leakage from mesophyll and vascular parenchyma cells. A selective release of transport oligosaccharides was not observed. The experimental results presented here do not preclude a symplastic transfer of assimilates in mature leaves.Abbreviations EDTA
ethylenediaminetetraacetate
- EGTA
ethylene glycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetate
- PCMBS
p-chloromercuribenzenesulfonic acid 相似文献
440.
Micropropagation of mature siberian elm in two steps 总被引:1,自引:1,他引:0
A simple and reliable two-step micropropagation system was developed for mature Siberian elm (Ulmus pumila L.). Shoot-tip cultures were initiated and multiplied on a modified Murashige and Skoog medium supplemented with 1 M benzyladenine, B5 vitamins, solidified with 0.22% Gelrite, and subcultured weekly. Proliferated shoots 2–3 cm in length rooted successfully in sterile and non-sterile soil mix at 100% efficiency. Healthy plants were acclimatized to the ambient environment.Abbreviations 2,4-D
2,4-dichlorophenoxyacetic acid
- BA
benzyladenine
- IBA
indole-3-butyric acid
- MS
Murashige & Skoog medium (1962) 相似文献