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31.
A technique involving culture in soft agar was used for the assay of forward mutation of V79 cells to 6-thioguanine (6TG) resistance. The main reason for the use of soft agar was to prevent reduction in recovery of mutants depending on the cell density plated for mutation selection, which is the chief problem in the liquid method, and which results mainly from metabolic co-operation due to cell-to-cell contact.V79 cells grew well in fortified soft agar medium (DMEM + 20% FBS) showing cloning efficiencies (>80%) as high as in liquid culture. Therefore, V79/HGPRT mutagenesis could be assayed quantitatively in soft agar culture.The frequency of 6TG-resistant colonies in agar selective medium increased linearly with increase in concentration of EMS. Toxicity and mutagenic responses were greater in soft agar than in liquid culture.In cultures of untreated and EMS-treated cells, more than 95% of the 6TG-resistant colonies isolated were aminopterin-sensitive.Use of soft agar for selection prevented the reduction in the number of mutants with increase in the size of incula on plating up to 1?2 × 106 cells per 9-cm dish: in liquid culture, even with a lower plating number (2 × 105 cells per 9-cm dish), a notable reduction in numbers of mutants was observed. This character was re-examined in a reconstruction experiment. The results show that, when up to 2 × 106 cells were plated per 9-cm dish, 6TG-resistant cells were almost completely recovered from the soft agar medium, whereas only 10% were recovered from liquid culture. 相似文献
32.
Neopterin Retards Loss of Serotonin N-Acetyltransferase Activity from Cultured Chick Pineal Glands 总被引:1,自引:1,他引:0
Abstract: d -Neopterin at 10 μ M delayed start of the decline of serotonin N -acetyltransferase (NAT) activity from the peak level in the cycle exhibited by chick pineal glands cultured under standard conditions in the dark. A less marked retardation of decline of NAT activity was found with glands cultured under diurnal illumination or those exposed prematurely to light. There were no significant effects of neopterin on the increases of NAT activity or peak levels of activity developed. The pteridine also retarded loss of NAT activity from the peak level developed in the dark when the time of explanting into culture was later in the (solar) day, but not when it was earlier. Neopterin had no effect on the cycle in cyclic GMP content of cultured chick pineal glands. 相似文献
33.
The developmental influence of neuron-target interaction upon transmitter synthesis from labeled precursor and the capacity to release labeled transmitter were examined in dispersed cell cultures of embryonic ciliary ganglion neurons by comparing cultures of neurons plated alone and neurons plated upon pectoral myotubes. Of the total ACh synthesized from radiolabeled choline by neurons plated alone, more than half is via a Na+-dependent path, but a larger fraction of the synthesis is Na+ insensitive in culture than in mature neurons in vivo. In addition, at 1 week in culture the neurons lacking target failed to significantly increase ACh synthesis from the labeled choline in response to a previous high [K+]0 depolarization. Synthetic responsiveness to depolarization is a characteristic of mature nerve terminals in this preparation. One week after plating neurons onto myotube cultures, synthesis of ACh from the exogenous precursor is double that of sibling cultures lacking muscle, and prior depolarization with [K+]0 results in an increase in labeled product. Release from the labeled transmitter pool by the neurons with myotubes was also enhanced. [3H]ACh release elicited by depolarization via a Ca2+-dependent mechanism was more than fivefold higher in the cocultures. The influence of coculture with myotubes upon neuronal development is not duplicated by the neurons themselves despite formation of apparent interneuronal synapses (G. Crean, G. Pilar, J. Tuttle, and K. Vaca, 1982, J. Physiol. (London). 331, 87-104), by "fibroblasts" or medium conditioned over myotube cultures. Neurons under these conditions neither increase synthesis of [3H]ACh in response to a prior depolarization nor demonstrate enhanced basal [3H]ACh synthesis and release. Thus, coculture of embryonic ciliary ganglion neurons with a striated muscle target has a somewhat specific inductive effect, enhancing the capacity for neuronal [3H]ACh synthesis and release toward mature levels. This influence of a readily accessible target upon ciliary neuron cholinergic development in vitro may reflect a normal neuromuscular interaction occurring during embryogenesis. 相似文献
34.
We treat the transport of univalent cations through pore-like protein channels in biological membranes analytically, using two models (A + B) for the channel and the ion-channel interaction. A Lennard-Jones-type repulsion between the ions and the pore wall is introduced. We also include Van der Waals- and coulomb-type interactions between polar ligands of the pore-forming protein (e.g., carbonyl groups directed towards the axis of the channel) and the migrating particles. In model A, the polar groups are assumed to occur in pairs of dipoles pointing in opposite directions (as in the gramicidin A channel), while in model B the channel is treated as a pore with a radially isotropic charge distribution. In both models the ion-channel interaction leads to the occurrence of periodic potentials, corresponding to quasi-equilibrium and transition state sites of the ion in the pore. The diffusion rate can be calculated employing rate-theoretical concepts on the basis of microscopic parameters. It is demonstrated that the anomaly (inversion of the normal mass effect) for the transport rates of different ions can be related to differences in the activation entropy. The latter quantity is estimated analytically for both models. As a test, we performed numerical calculations with parameters based on the gramicidin A model. The results are in good agreement with experimental data and data from computer simulations. This shows that simple analytic expressions are well suited for predicting trends in the ionic conductivity of protein channels on the basis of microscopic interactions. 相似文献
35.
Biological control of thrips [Thysanoptera: Thripidae] on greenhouse cucumber byAmblyseius cucumeris
D. R. Gillespie 《BioControl》1989,34(2):185-192
The predatory miteAmblyseius cucumeris (Oudemans) [Acarina: Phytoseiidae] was evaluated as a biological control forThrips tabaci Lindeman andFrankliniella occidentalis (Pergande) [Thysanoptera: Thripidae] on greenhouse grown seedless cucumber.A. cucumeris spread throughout the greenhouses and provided control of both species of thrips.A. cucumeris adults persisted on plants for 7 weeks in the virtual absence of prey, and increased numerically in response to increases
in prey population. On the basis of these resultsA. cucumeris is recommended as a useful biological control forT. tabaci andF. occidentalis on greenhouse cucumber.
Publication No. 361, Agassiz Research Station, Agriculture Canada, Agassiz, B.C. Canada VOM 1AO. 相似文献
36.
Summary
Resinicium bicolor (Alb. & Schw. ex Fr.) Parm. [=Odontia bicolor (Alb. & Schw. ex Fr.) Bres.] is an outcrossing resupinate basidiomycete associated with root and butt rots of trees, but is itself only very weakly pathogenic. The distribution of genets among every spruce stump in a 70-year-old 1250 m2 spruce stand was analysed using somatic incompatibility testing. R. bicolor was present on 40% of 8-to 10-year-old stumps. Nineteen genets were found occupying 32 stumps; yielding probabilities of colonisation following establishment by basidiospores of 0.20–0.24 and by mycelial extension or dispersal of 0.16–0.20. The probability of colonisation decreased with increasing distance from a point of establishment. R. bicolor responded to both enrichment and destructive disturbances by the formation of an extensive cord system which enabled it to colonise discontinuously distributed resources and to overgrow fungi adjacent to it in a single resource unit, including Heterobasidion annosum. 相似文献
37.
Inheritance of antagonistic properties and lytic enzyme activities in sexual crosses of Talaromyces flavus 总被引:1,自引:0,他引:1
Two wild-type strains and three benomyl-resistant mutants of the antagonistic ascomycete Talaromyces flavus were crossed in six combinations, two of which yielded hybrid cleistothecia. Parental strains and their ascospore progenies varied in several traits considered to play an important role in the capacity to control soilborne fungal pathogens: extracellular activities of glucose oxidase and cell-wall degrading enzymes, antibiosis towards Verticillium dahliae, and parasitism and biocontrol of Sclerotium rolfsii. A non-Mendelian quantitative mode of inheritance was found for β-1, 3-glucanase and chitinase activities but only the latter exhibited a normal frequency distribution. Some of the progenies exhibited higher glucanase and chitinase activities than those found in the parental strains. Progeny analysis for chitinase, glucanase, cellulase, and glucose oxidase activities revealed no genetic association between any two of these enzymes. Antibiosis was correlated with glucose-oxidase activity in one cross, but not in the other. The ability to reduce bean root rot caused by S. rolfsii was correlated with mycoparasitic activity against S. rolfsii sclerotia in one cross, but not in the other. One out of the 20 progenies tested was able to reduce bean root rot more effectively than its parent strains, thus demonstrating the feasibility of improving a biocontrol agent by conventional breeding. 相似文献
38.
K. Thórarinsson 《BioControl》1990,35(1):107-118
Measurements of body length of cottony-cushion scales,Icerya purchasi Maskell, are presented. Although length increased markedly with developmental stage, the length distributions of successive
stages were found to overlap, making length an imperfect indicator of stage andvice versa. The likelihood of parasitism by the fly,Cryptochaetum iceryae (Williston), was found to increase with increasing scale size when scales of different sizes were concurrently made available
to the parasites under field conditions. Also, parasite loads (no. of parasites per parasitized host) were found to increase
with host size. The size ofC. iceryae pupae was found to depend on the developmental stage of the scale host in which pupation took place — the more developed
(larger) the host, the larger the pupa. This result suggests that parasite growth is food limited in the smaller hosts, and
that therefore its apparent preference for larger hosts is to the parasite's advantage.
相似文献
39.
Richard Stouthamer Robert F. Luck John D. Pinto Gary R. Platner Beth Stephens 《Entomologia Experimentalis et Applicata》1996,80(3):481-489
In non-reciprocal cross-incompatibility (NRCI), the crossing of a female of a strain A with a male of a strain B results in hybrid offspring, whereas the reciprocal cross produces few or no hybrids. Only females are of hybrid origin in Hymenoptera because they arise from fertilized eggs; males arise from unfertilized (haploid) eggs. Crosses between many strains of Trichogramma deion showed some degree of NRCI. Crosses between a T. deion culture collected in Seven Pines, California (SVP) with one from Marysville, California (MRY) showed an extreme form of NRCI in which practically no female offspring was produced when MRY females were crossed with SVP males. The reciprocal cross produced a close to normal proportion of female and male offspring. Detailed studied of this cross indicated that 1) the female offspring produced in the compatible interstrain cross were not the result of parthenogenesis but were true hybrids, 2) the incompatible interstrain cross did not produce female offspring because fertilized eggs died during development, 3) the death of these eggs could not be prevented by either antibiotic or temperature treatment, 4) cytoplasmically inherited factors causing NRCI could be discounted because backcrossed females with the genome of MRY and the cytoplasm of SVP, exhibit the NRCI relationship characteristic of their genome. Therefore the NRCI between these strains appears to be caused by a modification coded for by the nuclear genes of MRY that results in incompatibility when SVP sperm fertilizes MRY eggs. In addition the level of incompatibility in crosses between the SVP females and MRY males is temperature sensitive, the higher the rearing temperature the lower the level of compatibility. 相似文献
40.
A native nitrogen-fixing shrub facilitates weed invasion 总被引:33,自引:0,他引:33
Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds. 相似文献