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911.
Larkin PJ Gibson JM Mathesius U Weinman JJ Gartner E Hall E Tanner GJ Rolfe BG Djordjevic MA 《Transgenic research》1996,5(5):325-335
We report an improved method for white clover (Trifolium repens) transformation usingAgrobacterium tumefaciens. High efficiencies of transgenic plant production were achieved using cotyledons of imbibed mature seed. Transgenic plants were recovered routinely from over 50% of treated cotyledons. Thebar gene and phosphinothricin selection was shown to be a more effective selection system thannptII (kanamycin selection) oraadA (spectinomycin selection). White clover was transformed with the soybean auxin responsive promoter, GH3, fused to the GUS gene (-glucuronidase) to study the involvement of auxin in root development. Analysis of 12 independent transgenic plants showed that the location and pattern of GUS expression was consistent but the levels of expression varied. The level of GH3:GUS expression in untreated plants was enhanced specifically by auxin-treatment but the pattern of expression was not altered. Expression of the GH3:GUS fusion was not enhanced by other phytohormones. A consistent GUS expression pattern was evident in untreated plants presumably in response to endogenous auxin or to differences in auxin sensitivity in various clover tissues. In untreated plants, the pattern of GH3:GUS expression was consistent with physiological responses which are regarded as being auxin-mediated. For the first time it is shown that localised spots of GH3:GUS activity occurred in root cortical tissue opposite the sites where lateral roots subsequently were initiated. Newly formed lateral roots grew towards and through these islands of GH3:GUS expression, implying the importance of auxin in controlling lateral root development. Similarly, it is demonstrated for the first time that gravistimulated roots developed a rapid (within 1 h) induction of GH3:GUS activity in tissues on the non-elongating side of the responding root and this induction occurred concurrently with root curvature. These transgenic plants could be useful tools in determining the physiological and biochemical changes that occur during auxin-mediated responses. 相似文献
912.
The complete mitochondrial DNA (mtDNA) molecule of the gorilla was
sequenced. The entire sequence, 16,412 nucleotides, was determined by
analysis of natural (not polymerase chain reaction) restriction fragments
covering the whole molecule. The sequence was established from one
individual and thus nonchimeric. After comparison with the COII gene of
gorilla specimens with known geographical origin, the sequence was
identified as characteristic of the Western lowland gorilla, Gorilla
gorilla gorilla. With the exception of the NADH2 gene, all genes have a
methionine start codon. The inferred start codon of NADH2 is ATT
(isoleucine). The COIII, NASDH4, and cytochrome b genes are not terminated
by a stop codon triplet, and the COI gene is probably terminated by an AAA
triplet rather than by a regular stop codon. The great majority of genic
sequences (rRNAs, peptide-coding genes, tRNAs) of the complete mtDNAs of
Gorilla, Pan, and Homo show a greater similarity between Pan and Homo than
between either of these genera to Gorilla. The analysis of the
peptide-coding genes suggest that relative to comparison between Homo and
Pan a certain degree of transition saturation has taken place in codon
position 3 in comparisons between Gorilla to either Homo or Pan.
相似文献
913.
A New In Vivo Fluorimetric Technique To Measure Growth of Adhering Phototrophic Microorganisms 总被引:2,自引:0,他引:2 下载免费PDF全文
We developed a noninvasive rapid fluorimetric method for the investigation of growth of adhering (benthic) phototrophic microorganisms. The technique is based on the sensitive detection of the in vivo fluorescence of chlorophylls chlorophyll a and bacteriochlorophyll a and monitors increases in signal over time as an indicator for growth. The growth fluorimeter uses modulated excitation light of blue-light-emitting diodes and a photodiode as the detector. The light-emitting diodes are mounted geometrically in an aluminum housing for efficient and uniform illumination of the bottoms of the growth containers. The fluorimeter was characterized with respect to detection limit and dynamic range. This system is capable of resolving in vivo chlorophyll a concentrations of 0.5 (mu)g liter(sup-1) in cyanobacteria and 0.03 (mu)g liter(sup-1) in diatoms as well as in vivo bacteriochlorophyll a concentrations in phototrophic bacteria of 0.3 (mu)g liter(sup-1), which points to an extremely high sensitivity compared with that of similar available techniques. Thus, the new fluorimeter allows the determination of growth at extremely low cell densities. The instrument was used successfully to measure the growth of several adhering isolates of the filamentous cyanobacterium Microcoleus chthonoplastes from benthic microbial mats in seawater of different salinities. The data obtained demonstrate broad growth responses for all strains, which thus can be characterized as euryhaline organisms. 相似文献
914.
Dynamics in oxygen-induced changes in S-layer protein synthesis from Bacillus stearothermophilus PV72 and the S-layer-deficient variant T5 in continuous culture and studies of the cell wall composition. 总被引:1,自引:3,他引:1 下载免费PDF全文
M Sra B Kuen H F Mayer F Mandl K C Schuster U B Sleytr 《Journal of bacteriology》1996,178(7):2108-2117
Stable synthesis of the hexagonally ordered (p6) S-layer protein from the wild-type strain of Bacillus stearothermophilus PV72 could be achieved in continuous culture on complex medium only under oxygen-limited conditions when glucose was used as the sole carbon source. Depending on the adaptation of the wild-type strain to low oxygen supply, the dynamics in oxygen-induced changes in S-layer protein synthesis was different when the rate of aeration was increased to a level that allowed dissimilation of amino acids. If oxygen supply was increased at the beginning of continuous culture, synthesis of the p6 S-layer protein from the wild-type strain (encoded by the sbsA gene) was immediately stopped and replaced by that of a new type of S-layer protein (encoded by the sbsB gene) which assembled into an oblique (p2) lattice. In cells adapted to a prolonged low oxygen supply, first, low-level p2 S-layer protein synthesis and second, synchronous synthesis of comparable amounts of both types of S-layer proteins could be induced by stepwise increasing the rate of aeration. The time course of changes in S-layer protein synthesis was followed up by immunogold labelling of whole cells. Synthesis of the p2 S-layer protein could also be induced in the p6-deficient variant T5. Hybridization data obtained by applying the radiolabelled N-terminal and C-terminal sbsA fragments and the N-terminal sbsB fragment to the genomic DNA of all the three organisms indicated that changes in S-layer protein synthesis were accompanied by chromosomal rearrangement. Chemical analysis of peptidoglycan-containing sacculi and extraction and recrystallization experiments revealed that at least for the wild-type strain, a cell wall polymer consisting of N-acetylglucosamine and glucose is responsible for binding of the p6 S-layer protein to the rigid cell wall layer. 相似文献
915.
916.
917.
SUMMARY Data are presented on the occurrence of a surprising number of permanent water sources on the gravel plains of the Namib-Naukluft Park, South West Africa. As a consequence, no game animal is further than ca 25 km away from the nearest watering-place. Within a broad range of ionic contents, the surface waters of the desert display a marked similarity in their chemical composition, being mainly dominated by Na+>Ca++>Mg++: Cl?>SO4 ?>HCO3 ??CO3- ?. Evaporation, precipitation and rock dominance seem to be the main controlling mechanisms involved in determining the chemical composition of the waters. 相似文献
918.
L-lactate transport mechanism across rat jejunal enterocyte was investigated using isolated membrane vesicles. In basolateral
membrane vesicles l-lactate uptake is stimulated by an inwardly directed H+ gradient; the effect of the pH difference is drastically reduced by FCCP, pCMBS and phloretin, while furosemide is ineffective.
The pH gradient effect is strongly temperature dependent. The initial rate of the proton gradient-induced lactate uptake is
saturable with respect to external lactate with a K
m
of 39.2 ± 4.8 mm and a J
max of 8.9 ± 0.7 nmoles mg protein−1 sec−1. A very small conductive pathway for l-lactate is present in basolateral membranes. In brush border membrane vesicles both Na+ and H+ gradients exert a small stimulatory effect on lactate uptake. We conclude that rat jejunal basolateral membrane contains
a H+-lactate cotransporter, whereas in the apical membrane both H+-lactate and Na+-lactate cotransporters are present, even if they exhibit a low transport rate.
Received: 22 October 1996/Revised: 11 March 1997 相似文献
919.
Two diastereomeric nicotinamide adenine dinucleotide (NAD+) derivatives were synthesized in which the substrates of (S)-and (R)-lactate-specific dehydrogenases are covalently attached via a methylene spacer at position 5 of the nicotinamide ring. The corresponding nicotinamide derivatives were obtained stereospecifically by enzymatic reduction of 5-(2-oxalylethyl)nicotinamide. (3S)-5-(3-Carboxy-3-hydroxypropyl)-NAD+ undergoes and intramolecular hydride transfer in the presence of pig heart lactate dehydrogenase, forming the corresponding coenzyme-substrate analogue composed of pyruvate and NADH. No cross-reaction products resulting from an intermolecular reaction are observed. Two (R)-lactate specific dehydrogenases, however, do not catalyze a similar reaction in either one of the two diastereomers. A possible arrangement of the substrates in the active centers of these enzymes is proposed. 5-Methyl-NAD+ and 5-methyl-NADH are active coenzymes of pig heart lactate dehydrogenase in contrast to reports in the literature. (S)-Lactate binds to this enzyme in the absence of coenzyme, exhibiting a dissociation constant of 11 mM. 相似文献
920.
To clarify further the beneficial effect of thiazide diuretics on recurrent calcium nephrolithiasis, the effect of short-term hydrochlorothiazide therapy on urine saturation with brushite (CaHPO4·2H2O), in vitro collagen calcification by urine, and urinary inhibitors of calcification was studied.In 22 patients with idiopathic calcium oxalate/phosphate stones the urine calcium excretion decreased, the urine magnesium excretion increased and the urine magnesium/calcium ratio increased significantly (P < 0.001) during hydrochlorothiazide therapy. Supersaturation of the urine with brushite, which was present in 19 of the 22 patients, was reduced significantly (P < 0.001) in all during thiazide therapy, and to the undersaturated range in 16. The ability of urine to calcify collagen in vitro also decreased significantly (P < 0.001) during thiazide therapy, a change that correlated significantly (r = 0.4513, P < 0.05) with the decrease in brushite saturation. The concentration of urinary inhibitors of calcification, as determined with an in vitro collagen calcification system, was decreased significantly (P < 0.01) by thiazide therapy.It was concluded that, in addition to decreasing urine calcium excretion and increasing urine magnesium excretion, thiazide diuretics decrease the urinary brushite saturation and thus may prevent spontaneous nucleation or crystal growth, or both, of calcium phosphate. The ability of thiazides to decrease collagen calcification in vitro suggests that they may also prevent crystal growth on a nidus of organic matrix. Thiazides do not appear to act by increasing the excretion of urinary inhibitors of calcification. 相似文献