-
[show abstract]
[hide abstract]
ABSTRACT: Agave (Asparagaceae) includes cultivated and wild varieties of henequen used for hard fibre production. As part of a breeding programme to improve Agave production, species with different ploidy levels were genetically characterized: two diploids [A. tequiliana Weber and the hybrid H11648 ((A. amaniensis Trel. & Nowell × A. angustifolia Haw.) × A. amaniensis)], a triploid (A fourcroydes Lem. var. kitam ki), a tetraploid (A. angustifolia var. letona), three pentaploids (A. fourcroydes var. sac ki, A. fourcroydes var. yaax ki, and A. sisalana Perrine), and two hexaploids (A. angustifolia var. chelem ki from two locations). Chromosome spreading was used to determine the chromosome number, flow cytometry was employed to measure the genome size, and fluorescent in situ hybridization was performed using 45S and 5S ribosomal DNA (rDNA) and the telomeric sequences (TTAGGG)n and (TTTAGGG)n as genetic markers. There were proportional increases with ploidy level of the following: (1) chromosome number (from diploid 2n = 2x = 60 to hexaploid 2n = 6x = 180), including the number of large and small chromosomes in the bimodal karyotype of Agave; (2) genome size, with a mean monoploid genome size (1Cx) of 7.5 pg (range, 7.36–7.61 pg); and (3) the number and distribution of 45S and 5S rDNA loci, with one locus of each per basic, monoploid genome. Thus there was complete additivity in genome structure with increasing ploidy, as reported in some angiosperm polyploids. However, as other analyses of polyploids have revealed a decrease in 1Cx values with increased ploidy, possible explanations for the observed genomic stability were considered. With the (TTAGGG)n probe, the signal was localized at the telomeres, consistent with published data showing that many species in the order Asparagales have this type of telomere sequence. It is speculated that sporadic telomeric signals using the (TTTAGGG)n probe are probably derived from either errors in telomerase activity or relic ancestral-type telomeric sequences. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158, 215–222.
Botanical Journal of the Linnean Society 09/2008; 158(2):215 - 222. · 2.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A key target set at the second Plant Genome Size Workshop, held at the Royal Botanic Gardens, Kew in 2003, was to produce first DNA C-value data for an additional 1 % of angiosperm species, and, within this, to achieve 75 % familial coverage overall (up from approx. 50 %) by 2009. The present study targeted eudicot families for which representation in 2003 (42.5 %) was much lower than monocot (72.8 %) and basal angiosperm (69.0 %) families.
Flow cytometry or Feulgen microdensitometry were used to estimate nuclear DNA C-values, and chromosome counts were obtained where possible.
First nuclear DNA C-values are reported for 20 angiosperm families, including 18 eudicots. This substantially increases familial representation to 55.2 % for angiosperms and 48.5 % for eudicots.
The importance of targeting specific plant families to improve familial nuclear DNA C-value representation is reconfirmed. International collaboration will be increasingly essential to locate and obtain material of unsampled plant families, if the target set by the second Plant Genome Size Workshop is to be met.
Annals of Botany 01/2006; 96(7):1315-20. · 4.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Within Oncidiinae, there are several groups of species that are effectively annuals, and we wished to see if these species had smaller genome sizes than average for the subtribe.
Fifty-four genome size estimates (50 of which are new) for species in subtribe Oncidiinae (Orchidaceae) were examined for the first time in a phylogenetic context to evaluate hypotheses concerning genome sizes and life history traits.
Within the limits of still relatively sparse sampling, the species that are effectively annuals do appear to have smaller genome sizes than average. However, the genome sizes of their immediate sister group are also small, indicating that changes in genome size preceded the change in life history traits. Genome sizes and chromosome numbers also do not correlate; some slowly growing species have lower chromosome numbers but large genomes and vice versa. Based on a survey of the literature on orchids, it is also clear that epiphytic species have smaller genome sizes than do terrestrial species, which could be an effect of different water relations or the fact that most terrestrial orchids are geophytic or have distinct growth and dormancy phases.
Annals of Botany 02/2005; 95(1):191-9. · 4.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: This paper reports first DNA C-values for 28 angiosperm genera. These include first DNA C-values for 25 families, of which 16 are monocots. Overall familial representation is 47.2 % for angiosperms, but is now much higher for monocots (75 %) and basal angiosperms (73.1 %) than for eudicots (38.7 %). Chromosome counts are reported for 22 taxa, including first records for six genera plus seven species. Unrepresented families will become increasingly enriched for monotypic taxa from obscure locations that are harder to access. Thus, completing familial representation for genome size for angiosperms may prove impossible in any short period, and progress towards this goal will become slower.
Annals of Botany 02/2003; 91(1):31-8. · 4.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: C-values are important biodiversity characters, yet data for pteridophytes are scarce. A recent survey showed that reliable C-value data were available for only 62 species. This paper reports C-value estimates for a further five pteridophyte species which were selected to fill phylogenetic gaps identified in previous work: Angiopteris lygodiifolia, of the eusporangiate fern family Marattiaceae (1C = 7.10 pg); Lygodium japonicum, of the basal leptosporangiate fern family Schizaeaceae (1C = 11.66 pg); Marsilea quadrifolia, of the heterosporous water fern order Marsileales (1C = 4.01 pg); Isoetes lacustris (1C = 11.97 pg) and Lycopodium clavatum (1C = 2.86 pg), of the lycophyte families Isoetaceae and Lycopodiaceae, respectively. The C-value estimates are discussed in the context of other C-value data. Further, the range of C-values in lycophytes (0.16 pg – 11.97 pg), which comprise Selaginellaceae, Isoetaceae and Lycopodiaceae, is discussed in relation to nucleotypic constraints imposed by sperm flagella number. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140, 169−173.
Botanical Journal of the Linnean Society 10/2002; 140(2):169 - 173. · 2.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The evolutionary significance of the c. 1000-fold range of DNA C-values in angiosperms (1C = c. 0.1–127.4 pg) has often attracted interest. A recent analysis, which superimposed available C-value data onto the angiosperm phylogeny, that placed Ceratophyllaceae as the most basal angiosperm family led to the conclusion that ancestral angiosperms were characterized by small genomes (defined as 1C £ 3.5 pg). However, with the recent increase in DNA sequence data and large-scale phylogenetic analyses, strong support is now provided for Amborellaceae and/or Nymphaeaceae as the most basal angiosperm families, followed by Austrobaileyales (comprising Schisandraceae, Trimeniaceae and Austrobaileyaceae). Together these five families comprise the ANITA grade. The remaining basal angiosperm families (Ceratophyllaceae, Chloranthaceae and magnoliids), together with monocotyledons and eudicotyledons, form a strongly supported clade. A survey showed that C-value data were scarce in the basal angiosperm families, especially the ANITA grade. The present paper addresses these phylogenetic gaps by providing C-value estimates for each family in ANITA, together with C-values for species in Chloranthaceae, Ceratophyllaceae and a previously unrepresented family in the magnoliids, the Winteraceae. © The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140, 175–179.
Botanical Journal of the Linnean Society 10/2002; 140(2):175 - 179. · 2.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nuclear DNA C-values and genome size are important biodiversity characters with fundamental biological significance. Yet C-value data for pteridophytes, a diverse group of vascular plants with approx. 9000 extant species, remain scarce. A recent survey by Bennett and Leitch (2001, Annals of Botany 87: 335-345) found that C-values were reported for only 48 pteridophyte species. To improve phylogenetic representation in this group and to check previously reported estimates, C-values for 30 taxa in 17 families were measured using flow cytometry for all but one species. This technique proved generally applicable, but the ease with which C-value data were generated varied greatly between materials. Comparing the new data with those previously published revealed several large discrepancies. After discounting doubtful data, C-values for 62 pteridophyte species remained acceptable for analysis. The present work has increased the number of such species' C-values by 93 %, and more than doubled the number of families represented (from 10 to 21). Analysis shows that pteridophyte C-values vary approx. 450-fold, from 0-16 pg in Selaginella kraussiana to 72.7 pg in Psilotum nudum var. gasa. Superimposing C-value data onto a robust phylogeny of pteridophytes suggests some possible trends in C-value evolution and highlights areas for future work.
Annals of Botany 09/2002; 90(2):209-17. · 4.03 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A detailed description of ovule development and embryology ofHemiphylacus alatostylus is given, together with a chromosome count and karyotype. Comparative data are presented forAsparagus andAnemarrhena, since earlier analysis ofrbcL sequence data indicated a relationship between them.Hemiphylacus should be included inAsparagaceae. A close relationship between them is strongly supported byrbcL analysis, and they are further linked by the shape and histology of the fertilised ovule. However, both morphological and molecular data indicate thatAnemarrhena is a more isolated taxon.
Plant Systematics and Evolution 01/1998; 211(3):181-199. · 1.34 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Nuclear DNA C-value is an important genomic biodiversity character with many uses. An international workshop sponsored by Annals of Botany and held at the Royal Botanic Gardens, Kew, UK, in 1997 identified major gaps in our knowledge of plant DNA C-values and recommended targets for new work. Improved taxonomic coverage was highlighted as a key need for angiosperms, especially at the familial level. In 1997 C-values were known for only approx. 32% of angiosperm families; a goal of complete familial representation by 2002 was recommended. A review published in 2000 (Bennett et al. ; Annals of Botany 86 : 859–909) noted poor progress towards this aim: of the 691 first C-values for species only 12 (1.7%) were for unrepresented families. We began new work to address this in 1999, reporting first DNA C-values for 25 angiosperm families in 2001 (Hanson et al. ; Annals of Botany 87 : 251–258). Here we report first DNA C-values for a further 25 angiosperm families, increasing familial coverage in angiosperms to approx. 45%. Such targeting remains essential to approach the goal set by the 1997 workshop of familial coverage for angiosperms within 5 years. The 4C DNA amounts presented here range from 0.76 pg (similar to Arabidopsis thaliana ) in Roridula gorgonias (Roridulaceae) to 29.74 pg in Gunnera manicata (Gunneraceae). 1C values were < 3.5 pg in 23 of the 25 families; these data provide further support for the view that ancestral angiosperms almost certainly had small genomes (defined as 1C ⩽ 3.5 pg). Chromosome counts are reported for 20 taxa, including first records for one genus and five species. Copyright 2001 Annals of Botany Company
-
[show abstract]
[hide abstract]
ABSTRACT: The gymnosperms are a monophyletic yet diverse group of woody trees with approx. 730 extant species in 17 families. A recent survey showed that DNA C-values were available for approx. 16% of species, but for only 12 of the 17 families. This paper completes familial representation reporting first C-values for the five remaining families: Boweniaceae, Stangeriaceae, Welwitschiaceae, Cephalotaxaceae and Sciadopityaceae. C-values for nine Ephedra and two Gnetum species are also reported. C-values are now available for 152 (21%) species. Analysis confirms that gymnosperms are characterized by larger C-values than angiosperms (modal 1C of gymnosperms = 15.8 pg compared with 0.6 pg in angiosperms) although the range (1C = 2.25–32.20 pg) is smaller than that in angiosperms (1C = 0.05–127.4 pg). Given complete familial coverage for C-values and increasing consensus in gymnosperm phylogeny, the phylogenetic component of C-value variation was also investigated by comparing the two datasets. This analysis revealed that ancestral gymnosperms (represented by cycads and/or Ginkgo ; mean genome size = 14.71 pg) probably had larger genomes than ancestral angiosperms. Copyright 2001 Annals of Botany Company
-
[show abstract]
[hide abstract]
ABSTRACT: Of the world's 250000 angiosperm species, only about 200 are recognized as important weeds. 4C nuclear DNA amounts were estimated for 39 such species. Success for many important weeds is suggested to reflect several traits known to correlate with low DNA C-value, so such weeds may have smaller DNA C-values than other species. Our work tests this hypothesis, comparing DNA amounts in 156 species recognized as important world weeds or British garden weeds, with 2685 other species. DNA amounts did not differ significantly between the two weed samples, but weeds showed highly significant differences from other species. For example, nuclear DNA amount in weeds (mean 11·74 pg) was smaller than in other species (mean 28·13 pg), and restricted to the lowest 20% of their range. Similarly, DNA amount per genome in weeds (mean 3·79 pg) was smaller than in other species (mean 12·14 pg), and restricted to the lowest 10% of their range. As significant differences between weeds and other species remain for almost all sub-samples tested, this contrast is widely distributed. So it is important to ask how selection against high nuclear DNA amount and genome size in weeds operates. The probability of a species being a weed fell significantly with increasing nuclear 4C DNA amount, and mean genome size, reaching zero just above 100 pg, and 19 pg, respectively. Moreover, polyploidy was significantly more frequent in weeds (51%) than in other species (27%), increasing with nuclear DNA amount in both, reaching 100% in weeds with the highest 4C DNA amounts, but only 41% in other species. Thus, selection for polyploidy in weeds may partly reflect their increased genetic variability, independent of DNA amount. However, such selection pressure grows strongly with rising nuclear DNA amount, and this may act mainly on correlated factors including faster development.
