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M D Bennett

Publications and source records attributed to M D Bennett.

At least 19 recordsLinked to original sources
PubMed2000

Aloe L.--a second plant family without (TTTAGGG)n telomeres.

The physical ends of chromosomes are protected and stabilised by telomeres. The sequence of telomeric DNA normally consists of a simple repeating unit that is conserved in many organisms. Most plants examined have been shown to possess Arabidopsis-type telomeres consisting of many repeat copies of the sequence 5'-TTTAGGG-3'. Using fluorescent in situ hybridisation, slot blotting and the asymmetric polymerase chain reaction we demonstrate an absence of Arabidopsis-type telomeres in the genus Aloe (family Asphodelaceae). The only other plant genera so far reported without such telomeres are Allium, Nothoscordum, and Tulbaghia (family Alliaceae). As these genera and Aloe are petaloid monocots in the Asparagales, it is suggested that an absence of Arabidopsis-type telomeres may be characteristic of this related group of plants.

Allium↗
PubMed1999

Reference standards for determination of DNA content of plant nuclei.

Flow cytometry was used to compare 14 potential reference standards for plant DNA content determination. Both chicken and plant internal standards were used, as were propidium iodide (PI) and 4'-6-diamidino-2-phenylindole (DAPI) as fluorochromes. Means and standard errors of the means are presented for the 14 potential reference standards, and the means are compared to those obtained by Feulgen densitometry. Five species are recommended as an initial set of international standards for future plant DNA content determinations: Sorghum bicolor cv. Pioneer 8695 (2C = 1.74 pg), Pisum sativum cv. Minerva Maple (2C = 9.56 pg), Hordeum vulgare cv. Sultan (2C = 11.12 pg), Vicia faba (2C = 26.66 pg), and Allium cepa cv. Ailsa Craig (2C = 33.55 pg). It is recommended that the reference standard of choice be one with 2C and 4C nuclear DNA content peaks similar to, but not overlapping, the 2C and 4C peaks of the target species. We recommend PI as the fluorochrome of choice for flow cytometric determination of plant DNA content. DAPI should be used only if the estimated DNA value is corroborated by using a second stain that has no bias for AT- or GC-rich sequences within genomes.

Journal Article↗
PubMed1999

Genome structure and evolution in the allohexaploid weed Avena fatua L. (Poaceae).

Allohexaploid wild oat, Avena fatua L. (Poaceae; 2n = 6x = 42), is one of the world's worst weeds, yet unlike some of the other Avena hexaploids, its genomic structure has been relatively little researched. Consequently, in situ hybridisation was carried out on one accession of A. fatua using an 18S-25S ribosomal DNA (rDNA) sequence and genomic DNA from A. strigosa (AA-genome diploid) and A. clauda (CC-genome diploid) as probes. Comparing these results with those for other hexaploids studied previously: (i) confirmed that the genomic composition of A. fatua was similar to the other hexaploid Avena taxa (i.e., AACCDD), (ii) identified major sites of rDNA on three pairs of A/D-genome chromosomes, in common with other Avena hexaploids, and (iii) revealed eight chromosome pairs carrying intergenomic translocations between the A/D- and C-genomes in the accession studied. Based on karyotype structure, the identity of some of these recombinant chromosomes was proposed, and this showed that some of these could be divided into two types, (i) those common to all hexaploid Avena species analysed (3 translocations) and (ii) one translocation in this A. fatua accession not previously observed in reports on other hexaploid Avena species. If this translocation is found to be unique to A. fatua, then this information, combined with more traditional morphological data, will add support to the view that A. fatua is genetically distinct from other hexaploid Avena species and thus should retain its full specific status.

Avena↗
PubMed1998

Plant genome values: how much do we know?

Plants are the basis of life on earth. We cannot overemphasize their importance. The value of plant genome initiatives is self-evident. The need is to identify priorities for action. The angiosperm genome is highly variable, but the extent of this variability is unknown. Uncertainties remain about the number of genes and the number of species living. Many plants will become extinct before they are discovered. We risk losing both genes and vital information about plant uses. There are also major gaps in our karyotypic knowledge. No chromosome count exists for >70% of angiosperm species. DNA C values are known for only approximately 1% of angiosperms, a sample unrepresentative of the global flora. Researchers reported new relationships between genome size and characters of major interest for plant breeding and the environment and the need for more data. In 1997, a Royal Botanic Gardens Kew workshop identified gaps and planned international collaboration to fill them. An electronic version of the Angiosperm DNA C value database also was published. Another initiative, which will make a very significant contribution to the conservation of plant genetic diversity on a global scale is Kew's Millennium Seed Bank, partly funded by the U.K. Millennium Commission, celebrating the year 2000. Costing up to 80 million (1 = $1.62), its main aims are to collect and conserve the seed of almost all of the U.K. spermatophyte flora by the year 2000, to collect and conserve a further 10% of the world spermatophyte flora principally from the drylands by 2009, and to provide a world class building as the focus of this activity by 2000.

Journal Article↗
PubMed1997

Exogenous Neisseria meningitidis endophthalmitis.

PURPOSE: To report a case of Neisseria meningitidis endophthalmitis in association with a leaking filtering bleb and to consider antibiotic prophylaxis of those people with whom the patient had contact. METHOD: We treated an 81-year-old man who had a chronic, leaking filtering bleb and who developed exogenous N meningitidis endophthalmitis. RESULT: N meningitidis endophthalmitis was controlled with antibiotic therapy. Antibiotic prophylaxis for those with whom the patient had contact was not recommended. CONCLUSION: In this case, the N meningitidis strain was not considered invasive because the bacteria apparently entered the eye through a leaky filtering bleb and not through the bloodstream. Recovery of noninvasive N meningitidis does not require prophylaxis for patient contacts. In cases of endogenous or idiopathic N meningitidis endophthalmitis, antibiotic prophylaxis of close patient contacts may be warranted.

Aged↗
PubMed1997

The use of genomic in situ hybridization (GISH) to show transmission of recombinant chromosomes by a partially fertile bigeneric hybrid, Gasteria lutzii x Aloe aristata (Aloaceae), to its progeny.

Genomic in situ hybridization (GISH) was used to study somatic chromosomes of parental and progeny plants (all 2n=2x=14) of the bigeneric hybrid between Gasteria lutzii and Aloe aristata (Aloaceae), which is partially fertile, a rare occurrence in plants. GISH successfully distinguished between the two parental genomes in the F1 hybrid and revealed numerous genomic recombinations in chromosomes transmitted by the F1 to the back-cross progeny. The results indicate high levels of meiotic compatibility between the parental genomes, even though they differ in size by 20%. Recombination occurred at a frequency that was higher than that expected from the analysis of orcein-stained meiosis in the F1. The discrepancy suggests that terminalization may occur prior to or during metaphase I, reducing the apparent chiasma frequency, or possibly reveals an under-estimation caused by difficulties in resolving closely grouped chiasmata by eye.

Aloe↗
PubMed1996

The nucleotype, the natural karyotype and the ancestral genome.

New knowledge of synteny and collinearity promises to unify genetics and to affect our perception of higher order genome structure. This exciting new synthetic approach emphasizes genomic similarities rather than diversity. Two other aspects of genomic form and organisation, offering potentially unifying concepts in genome studies are: the nucleotype, and the natural karyotype. Genome size varies greatly between eukaryotes, and shows many strikingly precise correlations with phenotypic characters, independent of information encoded in DNA. Such nucleotypic correlations, based on biophysical absolutes, apply to all species, irrespective of genome size or chromosome number, and set limits on the range of phenotypes which can be expressed by genic control. Thus, knowledge of nucleotypic effects has considerable predictive value which can help to unify our understanding of genomes. Other studies of reconstructed nuclei have shown that: (1) the basic haploid genome exists as a real structural unit in nuclear architecture; while (2) the mean spatial arrangement of its heterologues also exists as a natural karyotype which is predictable using a simple model. Recently reported conceptual alignments of the maize genomes, which reflect the circularized ancestral grass genome, show interesting similarities with the orders of centromeres in their natural karyotypes predicted by the Bennett model. The basis of this phenomenon (if repeated in other species), and of selection which retains the ancestral genome form despite changes in basic chromosome number, may need to be explained. Perhaps the overall 3-D structure of the genome has some critical functional significance, essential for development. If so, a knowledge of this common structure would further unify our understanding of genomes and their evolution.

Biological Evolution↗
PubMed1995

Chromosomal location of endogenous geminivirus-related DNA sequences in Nicotiana tabacum L.

The N. tabacum (tobacco) nuclear genome carries approximately 25 multiple direct repeats of a geminivirus-related DNA (GRD) sequence that probably arose by illegitimate recombination, following geminivirus infection, during Nicotiana evolution. Each GRD repeat carries sequences similar to the geminiviral AL1 gene of the tomato golden mosaic virus (TGMV), encoding a protein required for viral DNA replication, plus the cis-essential replication origin. Using a cloned 14-kb GRD repeat sequence as a probe for fluorescence in situ hybridization (FISH), we identified a unique tobacco chromosome carrying GRD. Translocations between chromosomes of the tobacco S and T genomes were used as physical markers by sequentially hybridizing chromosomes with labelled GRD and total genomic DNA from N. sylvestris (equivalent to the S genome). The 25S, 18S and 5.8S ribosomal gene clusters were detected in double-labelling experiments for use as additional markers to identify the chromosomal location of GRD. GRD occupies one site on a homologous pair of small submetacentrics from the T genome characterized by a lack of either translocated segments from the S genome or ribosomal genes. GRD provides an additional marker for the small chromosomes of the T genome and a useful phylogenetic tool.

Chromosome Mapping↗
PubMed1995

Chromosome identification and mapping in the grass Zingeria biebersteiniana (2n = 4) using fluorochromes.

The grass Zingeria biebersteiniana is one of five angiosperms known with 2n = 2x = 4. Its chromosomes were studied using fluorochrome banding and fluorescence in situ hybridization (FISH). The large pericentromeric region fluoresced much more brightly on chromosome 2 than on chromosome 1, using two different fluorochrome banding methods. These offer rapid and reliable means for identifying chromosomes and work throughout mitosis. FISH located the major site of 18S-26S rDNA sequences at the secondary constriction, which is proximal to two minor sites, all on the short arm of chromosome 1. Two 5S sites were also detected, the most distinct on the short arm of chromosome 2 and the other apparently co-localized with part of the major 18S-26S rDNA cluster on chromosome 1. These results constitute the first steps in constructing a physical gene map for Z. biebersteiniana. Such information may facilitate future studies of the organization and reorganization of grass genomes, including research into the spatial arrangement of the genome in Zingeria nuclei and much wider comparisons of synteny and genome evolution in grasses.

Centromere↗
PubMed1995

Evidence for somatic translocation during potato dihaploid induction.

Potato dihaploid PDH55 (Solanum tuberosum) is exclusively euploid (2n = 24) but apparently contains and expresses DNA from dihaploid inducer IVP48 (S. phureja). Genomic in situ hybridization (GISH) suggested IVP48 DNA incorporated stably into PDH55 by somatic translocation. This finding has two important implications. Firstly, the long-held implicit assumption that euploid dihaploids produced by dihaploid inducers are pure S. tuberosum seems incorrect. This may complicate meiotic, genetical and molecular studies involving potato dihaploids. Secondly, if such translocations are not rare, the phenomenon may offer a novel way to introduce useful traits directly from wild dihaploid-inducing species into S. tuberosum.

Base Sequence↗
PubMed1994

Influenza vaccination programs for elderly persons: cost-effectiveness in a health maintenance organization.

OBJECTIVE: To estimate the cost-effectiveness and net medical care costs of programs for annual influenza vaccinations for the elderly in a health maintenance organization (HMO). DESIGN: Population-based, case-control study. SETTING: The Northwest Region of Kaiser Permanente, a prepaid group practice HMO in Portland, Oregon. PARTICIPANTS: Kaiser Permanente members 65 years of age and older who had at least 1 month of HMO eligibility during any of nine influenza seasons in the 1980s. MEASUREMENTS: The HMO's costs for providing medical care and conducting vaccination programs were estimated using accounting data. RESULTS: 32% of high-risk elderly persons and 22% of non-high-risk elderly persons received influenza vaccinations. Aggregate vaccine effectiveness in preventing pneumonia and influenza hospitalizations was 30% (95% CI, 17% to 42%) for high-risk and 40% (CI, 1% to 64%) for non-high-risk elderly persons. The net savings to the HMO per vaccination was $6.11 for high-risk elderly persons and $1.10 for all elderly persons. The HMO incurred a net cost of $4.82 per vaccination for non-high-risk elderly persons. CONCLUSIONS: Influenza vaccination rates in this HMO were relatively low for high-risk elderly persons. The medical care costs saved by preventing pneumonia and influenza through vaccination of high-risk elderly persons provide a compelling rationale to increase compliance with recommendations for annual influenza vaccination. Indirect benefits, such as prevention of suffering, incapacity, and lost wages, are likely to compensate for the small net cost of vaccinating non-high-risk elderly persons.

Aged↗
PubMed1994

Parental genome separation and asynchronous centromere division in interspecific F1 hybrids in Lathyrus.

Chromosomes were studied in root-tip metaphase cells of several F1 interspecific Lathyrus hybrids including: L. hirsutus x L. cassius (H x C), L. cassius x L. hirsutus (C x H), L. cassius x L. odoratus (C x O), and their parents, all with 2n = 2x = 14. Two types of morphologically distinct centromeres were identified in the hybrids on the basis of the degree of contraction of the primary constriction. At least 12 well-defined centromeres were seen in all cells of L. hirsutus, L. cassius and L. odoratus, and about 80% of cells had 14. The hybrids were more variable than the species. H x O contained between six and 14 well-defined centromeres, while cells of H x C, C x H and C x O all had seven well-defined and seven weakly defined centromeres. These were used as markers to plot their spatial disposition in two dimensions on metaphase spreads. In H x C, C x H and C x O the two types of centromeres showed a significant tendency to occupy two spatially distinct and concentrically arranged domains on the metaphase plate (P < 0.005). Owing to shortage of material subsequent work was restricted to H x C and C x H. Six or seven chromosomes of one parental genome were selectively labelled by in situ hybridization using biotinylated total genomic DNA from either parent as a probe. Moreover, there was a very strong correlation between centromere type and genomic origin (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Centromere↗
PubMed1993

Characterization of the Nicotiana tabacum L. genome by molecular cytogenetics.

Nicotiana tabacum (2n = 48) is a natural amphidiploid with component genomes S and T. We used non-radioactive in situ hybridization to provide physical chromosome markers for N. tabacum, and to determine the extant species most similar to the S and T genomes. Chromosomes of the S genome hybridized strongly to biotinylated total DNA from N. sylvestris, and showed the same physical localization of a tandemly repeated DNA sequence, HRS 60.1, confirming the close relationship between the S genome and N. sylvestris. Results of dot blot and in situ hybridizations of N. tabacum DNA to biotinylated total genomic DNA from N. tomentosiformis and N. otophora suggested that the T genome may derive from an introgressive hybrid between these two species. Moreover, a comparison of nucleolus-organizing chromosomes revealed that the nucleolus organizer region (NOR) most strongly expressed in N. tabacum had a very similar counterpart in N. otophora. Three different N. tabacum genotypes each had up to 9 homozygous translocations between chromosomes of the S and T genomes. Such translocations, which were either unilateral or reciprocal, demonstrate that intergenomic transfer of DNA has occurred in the amphidiploid, possibly accounting for some results of previous genetic and molecular analyses. Molecular cytogenetics of N. tabacum has identified new chromosome markers, providing a basis for physical gene mapping and showing that the amphidiploid genome has diverged structurally from its ancestral components.

Chromosome Mapping↗
PubMed1992

Genome reorganization in Nicotiana asymmetric somatic hybrids analysed by in situ hybridization.

In situ hybridization was used to examine genome reorganization in asymmetric somatic hybrids between Nicotiana plumbaginifolia and Nicotiana sylvestris obtained by fusion of gamma-irradiated protoplasts from one of the parents (donor) with non-irradiated protoplasts from the other (recipient). Probing with biotinylated total genomic DNA from either the donor or the recipient species unequivocally identified genetic material from both parents in 31 regenerant plants, each originating from a different nuclear hybrid colony. This method, termed genomic in situ hybridization (GISH), allowed intergenomic translocations containing chromosome segments from both species to be recognized in four regenerants. A probe homologous to the consensus sequence of the Arabidopsis thaliana telomeric repeat (5'-TTTAGGG-3')n, identified telomeres on all chromosomes, including 'mini-chromosomes' originating from the irradiated donor genome. Genomic in situ hybridization to plant chromosomes provides a rapid and reliable means of screening for recombinant genotypes in asymmetric somatic hybrids. Used in combination with other DNA probes, it also contributes to a greater understanding of the events responsible for genomic recovery and restabilization following genetic manipulation in vitro.

Cell Fusion↗
PubMed1990

Nuclear architecture in plants.

Structure within the nucleus of plants is becoming increasingly clear in both metaphase and interphase nuclei, although there are conflicting data about the relative positions of individual and pairs of chromosomes. At interphase, individual chromosomes may generally occupy discrete domains that are not intermixed with other chromosomes. Aspects of mechanical chromosome behaviour and even of gene expression may correlate with interphase chromosome position, and imply that a better understanding of nuclear architecture is required.

Cell Nucleus↗