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1.
T. E. Tautorus F. Bekkaoui M. Pilon R. S. S. Datla W. L. Crosby L. C. Fowke D. I. Dunstan 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,78(4):531-536
Summary Methods were developed for transient gene expression in protoplasts of black spruce (Picea mariana) and jack pine (Pinus banksiana). Protoplasts were isolated from embryogenic suspension cultures of black spruce and from non-embryogenic suspensions of jack pine. Using electroporation, transient expression of the chloramphenicol acetyltransferase (CAT) gene was assayed and shown to be affected by the cell line used, by voltage, temperature, and by the plasmid concentration and conformation. Increasing the plasmid DNA concentration (0–150g ml–1) resulted in higher levels of transient CAT expression. In jack pine, linearized plasmid gave 2.5 times higher levels of CAT enzyme activity than circular. Optimal voltage varied for each cell line of the two species within the range 200–350 V cm–1 (960 F). A heat shock treatment of protoplasts for 5 min at 45 °C resulted in enhanced CAT gene expression for both species.NRCC No. 30491 相似文献
2.
Primary productivity, biomass and chlorophyll-a of size fractionated phytoplankton (<0.22 m, <3 m, <8 m, <10 m, <40 m, <64 m, <112 m and <200 m) were estimated in 6 ponds and 5 experimental enclosures. The results showed that the planktonic algae less than 10 m are important in the biomass and production of phytoplankton in saline–alkaline ponds. The production of size fractionated phytoplankton corresponding to <112 m, <10 m and <3 m in saline–alkaline ponds were 10.5 ± 6.6 , 8.6 ± 5.4 and 0.33 ± 0.1 mgC l–1 d–1, respectively. Mean community respiration rate was 1.80 ± 0.73, 1.69 ± 0.90 and 1.38 ± 1.12 mgC l–1 d–1, respectively. The average production of phytoplankton corresponding to micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) were 1.61, 8.30 and 0.33 mgC l–1 d–1, respectively. The ratio of those to the total phytoplankton production was 15%, 79% and 3%, respectively. The mean respiration rate of the different size groups was 0.11, 0.31 and 1.38 mgC l–1 d–1; the ratio of those to total respiration of phytoplankton was 6%, 17% and 77%, respectively. The production of size-fractionated phytoplankton corresponding to <200 m, <10 m and <3 m in enclosures was 2.19 ± 1.63, 2.08 ± 1.75 and 0.22 ± 0.08 mgC l–1 d-1, respectively. Mean community respiration rates were 1.25 ± 1.55, 1.17 ± 1.42 and 0.47 ± 0.32 mgC l–1 d–1, respectively. The average production of phytoplankton corresponding to micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton was 0.11, 1.86 and 0.22 mgC l–1 d–1, respectively. The ratio of those to the total production of phytoplankton was 5%, 85% and 10%, respectively. The mean respiration rate of different size groups were 0.08, 0.72 and 0.46 mgC l–1 d–1, the ratio of those to total respiration of phytoplankton was 6%, 57% and 37%, respectively. The concentrations of chlorophyll-a of the phytoplankton in the corresponding size of micro- (10–112 m), nano- (3–10 m) and pico- (<3 m) plankton in the experimental ponds were 19.3, 98.2 and 11. 9 g l–1, respectively. The ratio of those to the total chlorophyll-a was 15%, 76% and 9%, respectively. The concentrations of chlorophyll-a of phytoplankton micro- (10–200 m), nano- (3–10 m) and pico- (<3 m) plankton in enclosures were 1.7, 34.3 and 3.0 g l–1, respectively. The ratio of those to the total chlorophyll-a was 4%, 88% and 8%, respectively. 相似文献
3.
Effects of GNA and other mannose binding lectins on development and fecundity of the peach-potato aphid Myzus persicae 总被引:2,自引:0,他引:2
Nicolas Sauvion Yvan Rahbé Willy J. Peumans Els J. M. Van Damme John A. Gatehouse Angharad M. R. Gatehouse 《Entomologia Experimentalis et Applicata》1996,79(3):285-293
Three mannose-binding lectins were assayed in artificial diets for their toxic and growth-inhibitory effects on nymphal development of the peach-potato aphid Myzus persicae. The snowdrop (Galanthus nivalis) lectin GNA was the most toxic, with an induced nymphal mortality of 42% at 1500 g ml–1 (30 M) and an IC50 (50% growth inhibition) of 630 g ml–1 (13 M). The daffodil (Narcissus pseudonarcissus) lectin NPA and a garlic (Allium sativum) lectin ASA induced no significant mortality in the range 10–1500 g ml–1, but did result in growth inhibition of 59% (NPA) and 26% (ASA) at 1500 g ml–1 (40 M for NPA, 63 M for ASA). All three lectins were responsible for a slight but significant growth stimulation when ingested at 10 g ml–1, reaching +26%, +18% and +11% over the control values for the garlic lectin, the daffodil lectin and the snowdrop lectin, respectively. GNA, as well as the glucose/mannose binding lectin Concanavalin A, were also provided at sublethal doses throughout the life cycle of the aphids, and effects on adult performance were monitored. Adult survival was not significantly altered, but both lectins adversely affected total fecundity and the dynamics of reproduction, resulting in significant reduction in calculated r
ms
(population intrinsic rate of natural increase) on lectin-containing diets. These effects are discussed in relation to the use of transgenic plants expressing these toxic lectins for potential control of aphid populations. 相似文献
4.
Robert E. Foley James R. Spotila John P. Giesy Carolyn H. Wall 《Environmental Biology of Fishes》1978,3(4):361-367
Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l–1, = 49.0 ag l–1. Well water samples generally contained less than 10 g l–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l–1) and many samples exceeded the maximum permissible limit (50 g l–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g–1 ), X = 0.7 g g–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers. 相似文献
5.
Dhawan Sunita Shasany Ajit K. Arif Naqvi Ali Kumar Sushil Khanuja Suman P.S. 《Plant Cell, Tissue and Organ Culture》2003,75(1):87-94
In vitro raised shoots of Mentha arvensis L. were screened for menthol tolerance level by growing them in media containing 0–100 g ml–1 menthol. A total of 2850 regenerated shoots were step wise screened for menthol tolerance at the concentrations of 50 g ml–1 followed by 60 and 70 g ml–1. In this screening, only 30 individual regenerated shoots were able to survive. The clones from the primary screen were inoculated into rooting medium and, after rooting, transferred to pots in the greenhouse. Ultimately, these 30 menthol tolerant clones were multiplied and grown in the field in replicated plots of 2.5×2.5 m sizes. Twigs of 30 clones from the replicated trials were rechecked for tolerant phenotypes at a concentration of 70 g ml–1 menthol wherein, these survived even after 7 days (secondary screening). These clones were checked for oil and menthol content and were found to be better than the control plants. Out of these 30 plants, five tolerated 80 g ml–1 menthol (tertiary level screening) and were found to contain the highest amount of menthol per g leaf biomass. Molecular analysis through RAPD showed distinct variation in the profiles of these five plants, in comparison to the control. Using this method the relationship between the primer OPT 04, menthol tolerance and high menthol content character of the genotype was established. Further, a cultivar `Saksham' was released from the selections by CIMAP for superior performance. 相似文献
6.
E. A. C. MacRobbie 《The Journal of membrane biology》1980,53(3):189-198
Summary Observations of aperture changes as sucrose is added to the solution bathing epidermal strips ofCommelina communis L. allow calculation of the osmotic changes required to open or close the stomatal pore, for comparison with changes in potassium content. With isolated guard cells, in strips in which all cells other than guard cells have been killed, the internal osmotic changes required are 83 mosmol kg–1 m–1 below 10m aperture, 129 mosmol kg–1 m–1 in the range 10–15 m, and 180 mosmol kg–1 m–1 above 15 m. For opening against subsidiary cell turgor in addition to guard cell turgor, in intact strips with live subsidiary and epidermal cells, these figures should each be increased by about 33 mosmol kg–1 m–1. A change in subsidiary cell turgor is magnified in its effects on the water relations of the guard cell by a factor greater than 3.7 for equal changes in the water potential of the two cells, or greater than 4.7 at constant volume of the guard cell. 相似文献
7.
Desana Li >sková José Ruiz Ordóñez Alexander Lux Alfredo Piñeyro López 《Plant Cell, Tissue and Organ Culture》1994,36(3):339-343
Isolated embryos ofKarwinskia humboldtiana were cultured in vitro. The growth of embryos and development to plantlets on woody plant medium supplemented with indole-3-acetic acid 6.10-2 mol l–1, gibberellic acid (GA3) 3.10-2 mol l–1, and 6-benzylaminopurine (BA) 2 mol l–1 was obtained. Multiplication of shoots and rooting of excised shoots has been achieved. Callus formation on modified Murashige-Skoog medium supplemented with 1-naphthaleneacetic acid 10 mol l–1, GA3 14 mol l–1, and kinetin 5 mol l–1 on hypocotyls, or on root cultures on medium supplemented with 2.4-dichlorophenoxyacetic acid 10 mol l–1 and BA 10 mol l–1 was induced.Abbreviations BA
6-benzylaminopurine
- 2,4-d
2,4-dichlorophenoxyacetic acid
- GA3
gibberellic acid
- IAA
indole-3-acetic acid
- NAA
1-naphthaleneacetic acid
- TEM
transmission electron microscopy 相似文献
8.
A eubacterium producing a blue pigment was isolated from a drinking water filter, and subsequently identified as Vogesella indigofera. This bacterium was further investigated for its morphological and biochemical characteristics after exposure to hexavalent chromium, Cr6+. The threshold Cr6+ concentration inhibiting the pigment production by V. indigofera was 200–300 g ml–1 in liquid cultures of nutrient broth and 100–150 g ml–1 on nutrient agar plates. The Cr6+ concentration preventing V. indigofera growth was 300–400 g ml–1 in liquid cultures, but greater than 150 g ml–1 on agar plates. Moreover, rugose colonies without the blue pigmentation were observed on agar plates amended with 150 (g Cr6+) ml–1. The biochemical utilization profiles of the colonies without pigmentation did not differ from the original pigment-producing ones, indicating phenotypic plasticity of this bacterium. The difference of phenotypic expression of V. indigofera under various Cr6+ concentrations might have potential application as a pollution bioindicator for heavy metals. 相似文献
9.
Pesticides and heavy metals in Danish streambed sediment 总被引:2,自引:0,他引:2
The role of streambed sediment as a sink for pesticides and heavy metals was investigated in 30 Danish lowland streams. The investigated streams drain catchments varying in hydrology, topography, soil type and land use. The <250 m newly accumulated fraction of the uppermost 1–2 cm layer of streambed sediment was analysed for 19 old and modern pesticides and 9 heavy metals. DDE was present in the sediment of all the streams. Of the herbicides, fungicides and insecticides currently in use, the most frequently detected was diuron (50.0%), fenpropimorph (66.7%) and lambda-cyhalothrin (6.7%), respectively. The pesticides detected in the highest concentration were fenpropimorph (1700 ng g–1), propiconazole (130 ng g–1) and isoproturon (110 ng g–1). The heavy metals are listed in order of increasing median concentration: Cd (0.80 g g–1), Co (9.1 g g–1), As (12.0 g g–1), Ni (19.0 g g–1), Cr (19.2 g g–1), Pb (19.7 g g–1), Cu (20.1 g g–1), V (28.5 g g–1), Zn (103 g g–1). The average number of pesticides detected in the 27 streams draining predominantly agricultural catchments was (3.7±2.0) being higher (p=0.077) than in the three streams draining non-agricultural catchments (1.7±0.6). Pesticides were significantly related to catchment size, soil type and hydrological regime. Several heavy metals (Cr, Cu, Pb, V and Zn) were related to urban activity and soil type. 相似文献
10.
J. Zhang V. K. Tiwari T. J. Golds N. W. Blackhall E. C. Cocking B. J. Mulligan J. B. Power M. R. Davey 《Plant Cell, Tissue and Organ Culture》1995,41(2):125-138
Cat gene expression has been investigated following PEG-mediated plasmid uptake into barley protoplasts. The uptake conditions optimised for transient expression were employed for stable transformation. Transformed protoplast-derived calli of the cvs. Dissa and Igri, were selected on medium containing G418 at 40 g ml–1 or kanamycin sulphate at 250 g ml–1. Absolute transformation frequencies of 28.9×10–5 and 21.3×10–5 were recorded for Dissa with kanamycin sulphate and G418 selection, respectively. The frequency for Igri was 11.5×10–5 with G418 selection. Antibiotic resistant protoplast-derived colonies expressed NPTII activity; Southern hybridisation confirmed integration of the nptII gene into barley genomic DNA.Abbreviations ABA
abscisic acid
- AC-CAP
acetylated chloramphenicol
- BAP
6-benzylaminopurine
-
cat
chloramphenicol acetyltransferase gene
- CAT
chloramphenicol acetyltransferase activity
- CaMV
cauliflower mosaic virus
- CAP
chloramphenicol, 2,4-d-2,4-dichlorophenoxyacetic acid
- GA3
gibberellic acid
- G418
Geneticin
-
gus
-glucuronidase gene
- HEPES
(N[2-hydroxyethyl] piperazine-N-[2-ethanesulphonic acid])
- IAA
indole acetic acid
- MES
2-N-morpholinoethane sulphonic acid
- NAA
-naphthaleneacetic acid
-
npt II
neomycin phosphotransferase gene
- NPTH
neomycin phosphotransferase activity
- PEG
polyethylene glycol
- SCV
settled cell volume 相似文献
11.
Irini Theodossiou Morten A. Olander Michael Søndergaard Owen R.T. Thomas 《Biotechnology letters》2000,22(24):1929-1933
A 20–40 m pellicular high density (3.7 g cm–3) expanded bed material has been designed for the capture of DNA and other large macromolecules. Anion exchangers fashioned out of these supports exhibited dramatically enhanced DNA binding capacities over commercial anion exchange adsorbents (6 mg ml–1, c.f. 50 g ml–1 at 10% breakthrough), due to a combination of small particle and fuzzy surface architecture created through the coupling of polyethylene imine chains. 相似文献
12.
Jae-Suk Choi Ji-Young Cho Long-Guo Jin Hyung-Joo Jin Yong-Ki Hong 《Journal of applied phycology》2002,14(2):115-121
In order to maintain axenic seedstock cultures axenically of thecommercially important red seaweed, Porphyra yezoensis, aprocedure was developed for axenic isolation and culture of conchocelis andmonospores. For axenic isolation of the conchocelis, contaminated microalgaewere most effectively removed by filtering contaminated samples through a100-m mesh after sonication. Removal of bacteria and otheralgaewas accomplished using a mixture of 5 agents (0.02% chitosan, 100 gml–1 GeO2, 10 gml–1 ampicillin, 40 gml–1 kanamycin and 200 gml–1 streptomycin). Axenic single colonies wereisolatedfrom a semi-solid medium prepared from 1% transfer gel. After collectingmonospores from the 40–50% density layer on a percoll-gradient, removalofbacteria and fungi from the monospores was accomplished using a mixture of 5antibiotics (3.5 g ml–1 nystatin, 2 mgml–1 ampicillin, 400 gml–1 kanamycin, 50 gml–1 neomycin and 800 gml–1 streptomycin). Axenic single juvenile blades wereisolated from a semi-solid medium prepared from 0.5% transfer gel. 相似文献
13.
Effect of tree distance on N2O and CH4-fluxes from soils in temperate forest ecosystems 总被引:5,自引:2,他引:3
Complete annual cycles of N2O and CH4 flux in forest soils at a beech and at a spruce site at the Höglwald Forest were followed in 1997 by use of fully automatic measuring systems. In order to test if on a microsite scale differences in the magnitude of trace gas exchange between e.g. areas in direct vicinity of stems and areas in the interstem region at both sites exist, tree chambers and gradient chambers were installed in addition to the already existing interstem chambers at our sites. N2O fluxes were in a range of –4.6–473.3 g N2O-N m–2 h–1 at the beech site and in a range of –3.7–167.2 g N2O-N m–2 h–1 at the spruce site, respectively. Highest N2O emissions were observed during and at the end of a prolonged frost period, thereby further supporting previous findings that frost periods are of crucial importance for controlling annual N2O losses from temperate forests. Fluxes of CH4 were in a range of +10.4––194.0 g CH4 m–2 h–1 at the beech site and in a range of –4.4––83.5 g CH4 m–2 h–1 at the spruce site. In general, both N2O-fluxes as well as CH4-fluxes were higher at the beech site. On a microsite scale, N2O and CH4 fluxes at the beech site were highest within the stem area (annual mean: 49.6±3.3 g N2O-N m–2 h–1; –77.2±3.1 g CH4 m–2 h–1), and significantly lower within interstem areas (18.5±1.4 g N2O-N m–2 h–1; –60.2±1.8 g CH4 m–2 h–1). Significantly higher values of total N, C and pH in the organic layer, as well as increased soil moisture, especially in spring, in the stem areas, are likely to contribute to the higher N2O fluxes within the stem area of the beech. Also for the spruce site, such differences in trace gas fluxes could be demonstrated to exist (mean annual N2O emission within (a) stem areas: 9.7±0.9 g N2O-N m–2 h–1 and (b) interstem areas: 6.2±0.6 g N2O-N m–2 h–1; mean annual CH4 uptake within (a) stem areas: –26.1±0.6 g CH4 m–2 h–1 and (b) interstem areas: –38.4±0.8 g CH4 m–2 h–1), though they were not as pronounced as at the beech site. 相似文献
14.
N.P. Markwick J.T. Christeller L.C. Dochterty C.M. Lilley 《Entomologia Experimentalis et Applicata》2001,98(1):59-66
Two biotin-binding proteins, avidin and streptavidin, were found to be insecticidal to the larvae of four species of Lepidoptera – light brown apple moth, Epiphyas postvittana (Walker) (fam. Tortricidae), green-headed leaf-roller, Planotortrix octo (Dugdale) (fam. Tortricidae), brown-headed leaf-roller, Ctenopseustis obliquana (Walker) (fam. Tortricidae) and potato tuber moth, Phthorimaea operculella (Zeller) (fam. Gelechiidae). Mortality occurred in all species, but there was a wide range in susceptibility. P. operculella larvae were the most susceptible with an LC50 of respectively, 2.3 g ml–1 for avidin and 1.4 g ml–1 for streptavidin after 9 days. E. postvittana larvae had an LC50 of 43.4 g ml–1 for avidin after 21 days, and C. obliquana larvae of 45.7 g ml–1 for avidin after 28 days. Although significant mortality occurred in P.octo at the highest doses of avidin, there was no sufficient dose-mortality response to calculate an LC50 for this species. For all species mortality curves were steep over a close range of doses followed by a plateau where mortality did not increase significantly with dose and did not reach 100%. Mortality was significantly affected by the amount of biotin in the diet on which the parental generation had been reared. Where this was rich in biotin, significant mortality of the offspring was much lower: larval offspring of a colony of E. postvittana, reared for five generations on a biotin-free diet had an LC50 of 5.1 g ml–1 after 14 days compared with 76.7 g ml–1 for larvae from a colony reared on general purpose diet. The implications for use of these proteins to confer insect resistance on transgenic plants are discussed. 相似文献
15.
Sabine P. Kuhn Robert M. Pfister 《Journal of industrial microbiology & biotechnology》1990,6(2):123-128
Summary
Zoogloea ramigera 115 was immobilized into beads of calcium-alginate and placed into batch air-bubbled column reactors. In the absence of any added nutrients the immobilized bacterium adsorbed Cd from solutions containing levels of 2 and 20 g ml–1 per day, over a period of 21 and 20 days, respectively. Adsorption of Cd from solutions containing 20 g ml–1 Cd was better than 90% for 16 days. Beads treated with Cd at 2 g ml–1 never adsorbed less than 95% of the metal. Alginate adsorbed Cd as well, but inclusion of cells changed the effectiveness of adsorption. Of a 250 g ml–1 Cd solution, alginate adsorbed 70.4% Cd in 60 min whereas alginate plus cells adsorbed 90.5% in the same time span. Temperature had no effect on adsorption by immobilized cells at levels of 2 and 10 g ml–1 Cd. However at higher concentrations, binding was enhanced as temperature increased.Z. ramigera beads were stable during all treatments and for prolonged periods of time (21 days). 相似文献
16.
Conditions were established for the introduction of both tobacco mosaic virus (TMV) and cucumber mosaic virus (CMV) RNAs into tobacco mesophyll protoplasts by electroporation. The proportion of infected protoplasts was quantified by staining with viral coat protein-specific antibodies conjugated to fluorescein isothiocyanate. Approximately 30–40% of the protoplasts survived electroporation. Under optimal conditions, up to 75% of these were infected with TMV-RNA. Successful infection was demonstrated in 19 out of 20 experiments. Optimal infection was achieved with several direct current pulses of 90 sec at a field strength of 5 to 10 kV/cm. Changing the position of the protoplasts within the chamber between electric pulses was essential for achievement of high rates of infection. Optimal viral RNA concentration was about 10 g/ml in a solution of 0.5 M mannitol without buffer salts. 相似文献
17.
Immature maize (Zea mays L.) embryos were treated with aflatoxin B1 concentrations, ranging from 0.1 g ml–1 to 25 g ml–1. Below 5 g ml–1 aflatoxin B1, root and shoot elongation was not significantly inhibited. Ultrastructurally, root tip cells showed little deterioration, except a possible diffused clearing in mitochondria and plastids. As the toxin concentration was increased above 5 gml–1, shoot, and particularly root elongation, was progressively inhibited. Associated with this, there was an apparent decrease in the ribosome population. Furthermore, membranes, particularly the vacuolar membrane, became abnormal and vacuolar distension occurred. At 20 and 25 g ml–1, these effects were exacerbated, and mitochondria and plastid structure was disrupted. At these concentrations, there was evidence of a disruption in lipid metabolism. The results are discussed in the context of known aflatoxin effects on cellular control mechanisms and ultrastructure in animal systems. 相似文献
18.
A method of measuring CO2gas exchange (caused, for example, by microalgal photosynthesis on emersed tidal mudflats) using open flow IR gas analyzers is described. The analyzers are integrated in a conventional portable photosynthesis system (LI-6400, LI-COR, Nebraska, USA), which allows manipulation and automatic recording of environmental parameters at the field site. Special bottomless measuring chambers are placed directly on the surface sediment. Measurements are performed under natural light conditions and ambient CO2concentrations, as well as under different CO2concentrations in air, and various PAR radiation levels produced by a LED light source built into one of the measurement chambers. First results from tidal channel banks in a north Brazilian mangrove system at Bragança (Pará, Brazil) under controlled conditions show a marked response of CO2assimilation to CO2concentration and to irradiance. Photosynthesis at 100molmol–1CO2in air in one sample of a well-developed algal mat was saturated at 309mol photons m–2s–1, but increased with increasing ambient CO2concentrations (350 and 1000mol mol–1CO2) in the measuring chamber. Net CO2assimilation was 0.8mol CO2m–2s–1at 100mol mol–1CO2, 5.9mol CO2m–2s–1at 350mol mol–1CO2and 9.8mol CO2m–2s–1at 1000mol mol–1CO2. Compensation irradiance decreased and apparent photon yield increased with ambient CO2concentration. Measurements under natural conditions resulted in a quick response of CO2exchange rates when light conditions changed. We recommend the measuring system for rapid estimations of benthic primary production and as a valuable field research tool in connection with certain ecophysiological aspects under changing environmental conditions. 相似文献
19.
J. Sybenga 《Genetica》1965,36(1):243-252
Whilst reliable estimates of chiasma frequencies can usually not be obtained, the probability (b) of a chromosome arm to be bound by at least one chiasma can often be determined. In the absence of interference this probability equals (1–e
–2), where 2 is the average chiasma frequency of the chromosome arm and the average crossover frequency or map length. In the presence of interference is shown to retain its genetic meaning as an additive metric that may describe the chromosome arm or other distinctive chromosome segment in terms of genetic recombination. It is a form of potential map length, comparable to, but numerically different from the regular map length. It is termed provisionally crossing-over potential.A chromosome with armsm andn with crossing-over potentials and will form ring bivalents with a frequency (1–e
–2).(1–e
–2); open bivalents with a frequency (1–e
–2).e
–2+(1–e
–2).e
–2; univalent pairs with a frequencye
–2.e
–2. Estimates of these frequencies yield equations from which and may be solved. In rye (Secale cereale) their ratio (q) is approximately two and differs from the mitotic arm length ratio of 1.4, indicating localization of chiasmata in the long arms.Graphs are given to show how, with constantq, the relation between the probabilitiesb
m
andb
n
of the two arms being bound changes with changing averageb.Data are presented on chiasma frequencies in M I, and compared with the frequencies expected in the absence of interference to give an impression of the degree of interference. Apparent fusion of chiasmata simulates interference. 相似文献
20.
A glasshouse experiment was conducted to study the effect of Ni on the growth and nutrients concentration in wheat (Triticum aestivum Cv. WH 291) in the presence and absence of applied N as urea. Responses to N application were observed up to 120 g N g–1 soil. No response to Ni was observed in the dry matter yield of wheat tops (leaves + stem) in the absence of applied N while in the presence of applied N, significant yield increases were obtained at 12.5g Ni g–1 soil. Nickel was not toxic to wheat up to 50g Ni g–1 soil in the presence of 120g N g–1 soil. Nitrogen and Ni concentration in wheat tops and roots increased with increasing levels of applied N and Ni, respectively. Applied Ni had an antagonistic effect on N concentration. Similarly, N reduced the Ni concentration in the wheat tissues. Positive growth responses to Ni were associated with 22 and 15g Ni g–1 in wheat tops, in the presence of applied N at 60 and 120g N g–1 soil, while Ni toxicity was associated with 63, 92.5 and 112.5g Ni g–1 in wheat tops, in the absence and presence of applied N at 60 and 120g N g–1 soil, respectively. 相似文献