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71.
Rapid In Situ Assay for Indoleacetic Acid Production by Bacteria Immobilized on a Nitrocellulose Membrane 总被引:8,自引:2,他引:6
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We have developed a new assay that differentiates between indoleacetic acid (IAA)-producing and -nonproducing bacteria on a colony plate lift. Medium supplemented with 5 mM L-tryptophan is inoculated with isolates of interest, overlaid with a nitrocellulose membrane, and then incubated until bacterial colonies reach 1 to 2 mm in diameter. The membrane is removed to a filter paper saturated with Salkowski reagent and incubated until distinct red haloes form around the colonies. The colorimetric reaction to IAA is limited to a region immediately surrounding each colony, is specific to isolates producing IAA, occurs within 1 h after the membrane is placed in the reagent, and is sensitive to as little as 50 pmol of IAA in a 2-mm2 spot. We have used this assay for quantifying epiphytic and endophytic populations of IAA-producing isolates of Pseudomonas syringae subsp. savastanoi and for detecting IAA-producing colonies of other pseudomonads and Erwinia herbicola. The assay provides a rapid and convenient method to screen large numbers of bacteria. 相似文献
72.
Communicated by R. N. Beachy 相似文献
73.
Sven Zea 《Helgoland Marine Research》1992,46(3):293-300
During a study of the spatial and temporal patterns of desmosponge (Porifera, Demospongiae) recruitment on rocky and coral
reef habitats of Santa Marta, Colombian Caribbean Sea, preliminary attempts were made to estimate actual settlement rates
from short-term (1 to a few days) recruitment censuses. Short-term recruitment rates on black, acrylic plastic plates attached
to open, non-cryptic substratum by anchor screws were low and variable (0–5 recruits/plate in 1–2 days, sets of n=5–10 plates),
but reflected the depth and seasonal trends found using mid-term (1 to a few months) censusing intervals. Moreover, mortality
of recruits during 1–2 day intervals was low (0–12%). Thus, short-term censusing intervals can be used to estimate actual
settlement rates. To be able to make statistical comparisons, however, it is necessary to increase the number of recruits
per census by pooling data of n plates per set, and to have more than one set per site or treatment. 相似文献
74.
Synopsis The Río Bayano in eastern Panama is one of many tropical rivers in which bull sharks (Carcharhinus leucas) and largetooth sawfish (Pristis perotteti) have been known to occur. Since both species can osmoregulate in fresh water throughout life, theoretically, both could survive in landlocked situations for many years.P. perotteti reproduces in fresh water, butC. leucas ordinarily does not, so only the former would appear to have the potential for establishing a breeding stock in such a landlocked freshwater body.The damming of the Rio Bayano and the creation of a large impoundment in 1976 provides a test of the ability of members of both species trapped there to survive and to establish breeding stocks. In 1980 and 1981 three mature femaleC. leucas were found dead in Lake Bayano and three sub-adult femaleP. perotteti were taken by trammel net. These events confirm the ability of both to survive in fresh water for long periods, but the establishment of breeding stocks appears doubtful and the question may not be answered for many years. 相似文献
75.
Jorge Zorzopulos Sara DeLong Virginia Chapman Lloyd M. Kozloff 《Journal of cellular biochemistry》1982,18(3):363-375
The characteristics of pure preparations of short-tail fibers of bacteriophage T4 have been studied in the optical and electron microscope. Three main structures were observed: 1) spheres of 8.1 nm diameter; 2) fibers 43 nm long and 3.8 nm thick; and 3) fibers 54 nm long and 3.2 nm thick. Both types of fibers exhibited a regular beaded appearance. The 43-nm fibers were the most abundant structure. During the process of purification of the short-tail fibers, the formation of aggregates was observed each time the material containing the short-tail fibers was dialyzed against saline solutions. These aggregates became increasingly fibrous (as observed in the optical microscope) as the material used was increasingly enriched in short-tail fibers. Finally, most of the aggregates were of the fibrous type when they were formed from a purified preparation of short-tail fibers. In the electron microscope, it was found that the filamentous aggregates were organized in well-defined bundles. The amino acid composition of the highly purified short-tail fibers was also determined. Among the known fibrous proteins, the ones that most resemble the amino acid composition of the short-tail fibers are actin and fibrinogen. These observations are discussed in relation to the T4 short-tail fiber structure and their localization on the hexagonal baseplate of the T4 tail structure. 相似文献
76.
Plant tumor reversal associated with the loss of foreign DNA 总被引:1,自引:0,他引:1
Fun-Mei Yang Alice L. Montoya Eugene W. Nester Milton P. Gordon 《In vitro cellular & developmental biology. Plant》1980,16(1):87-92
Summary Transformation of plant tissues into crown gall tumors has been associated with the transfer of a portion of a tumor-inducing
plasmid (Ti-plasmid) into plant DNA. Various laboratories have regenerated normal-appearing plants from a number of crown
gall tumors. This study investigates the fate of the foreign DNA in a series of tissues derived from various parts of a plant
regenerated from the tumor BT-37 by Braun and his coworkers. It was found that all the foreign DNA sequences were lost from
tissues that had lost all their tumorous traits; whereas the plasmid DNA sequences were still present in tissues that appeared
normal but still exhibited tumorous traits when returned to tissue culture media. From these studies it would appear that
the presence of the Ti-plasmid sequences in the plant DNA is required for the maintenance of the transformed state.
Presented in the Symposium on Gene Transfer, Differentiation and Neoplasia in Plant and Animal Cells at the 30th Annual Meeting
of the Tissue Culture Association, Seattle, Washington, June 10–14, 1979. This symposium was supported in part by Grant CA
26748 from the National Cancer Institute, DHEW, and Grant RD-67 from the American Cancer Society. 相似文献
77.
Marker rescue transformation by linear plasmid DNA in Bacillus subtilis 总被引:21,自引:0,他引:21
Although plasmid-free Bacillus subtilis cannot be transformed for markers carried by linear or nicked plasmid DNA, a resident plasmid can rescue a marker on such damaged DNA under certain conditions. Linearized chimeric plasmid DNA has been used to transform cultures carrying a resident plasmid which is homologous with a portion of the donor. This system has revealed the following properties of the marker rescue process: (1) It is recE dependent. (2) It requires the presence in the resident plasmid of sequences which are homologous to the donor. (3) When the selected marker is on a nonhomologous segment it must be flanked by segments which are homologous to the resident plasmid. (4) The efficiency of rescue varies in a regular way with the position of the linearizing cut. (5) Marker rescue is first order with respect to DNA concentration. These properties and other data are interpreted as providing a strong indication that marker rescue occurs by recombination, although an alternative explanation involving recE-dependent recircularization of the donor plasmid has not been eliminated. Our results also suggest that if the major pathway of marker rescue is by recombination, an average of 0.15 Mdal (single strand) must be removed from each donor DNA molecule or otherwise rendered unavailable for recombination and that the exchange frequency during transformational recombination is approximately 0.2 to 0.5 Mdal−1. 相似文献
78.
79.
The existence of two types of binding sites for ouabain in human erythrocyte membranes is described. Receptor sites designated as ‘type I’, which may be identical to the K+-insensitive sites of intact cells, were detected at concentrations of ouabain as low as 10−7 M. The ‘type II’ receptor sites require the inclusion of Mg2+ + Pi to form complexes with ouabain; they may be identical to the K+-sensitive sites of intact cells. These sites were saturated at approx. 5 · 10−7 M ouabain but could not be detected at higher concentrations. The range of ouabain concentrations at which ‘type I’ receptors start to predominate (i.e. 5 · 10−8–5 · 10−7 M) was termed ‘critical digitalis concentrations’. The process of binding reached equilibrium within 1 and 4 h for ‘type I’ and ‘type II’ sites, respectively. The dissociation constant for ‘type II’ receptor-ouabain complexes was 7.6 · 10−9 M.Under similar experimental conditions, rat erythrocyte membranes exhibited only non-saturable sites.Alterations in the proportions of the two types of receptors were demonstrated by preincubation of the membranes, in the presence or absence of Mg2+ + Pi, prior to the addition of ouabain. In the first case, ‘type II receptor-ouabain’ complexes were stabilized at about 50% of the untreated membranes and ‘type I-ouabain’ complexes slowly approached equilibrium over a period of 24 h. In the latter instance, ‘type I’ receptors were not detected, and only ‘type II-ouabain’ complexes prevailed. 相似文献
80.
The concentration of prostaglandins of the E-group (PGE) and F-group (PGF) and the activity of prostaglandin-synthetase in rat ovaries increased on the evening of the day of proestrus and reached a peak at 5.00 h on the following morning, i.e. about the time of ovulation. Enzyme activity and PG concentrations receded to basal levels by 10.00 h on the day of estrus. These changes were prevented when the proestrous gonadotropin surge was blocked by administration of nembutal, and could be restored by administration of either LH or of FSH freed of LH contamination. The spontaneous preovulatory rise in prostaglandin concentration was about 6-fold for PGF and 30-fold for PGE, compared with values observed during the remainder of the cycle, whereas the rise in prostaglandin synthetase activity was only about 1.7-fold. The LH effect on PG accumulation had a latency of 2–4 h, which argues for enzyme synthesis rather than activation of preformed enzyme as the mechanism responsible. The small magnitude of the change in enzymic activity suggests that LH may, in addition, augment the availability of PG precursors. The results are compatible with the concept that prostaglandins play a physiological role in the gonadotropin-induced process of follicular rupture. 相似文献