First nuclear DNA amounts in more than 300 angiosperms

BACKGROUND AND AIMS: Genome size (DNA C-value) data are key biodiversity characters of fundamental significance used in a wide variety of biological fields. Since 1976, Bennett and colleagues have made scattered published and unpublished genome size data more widely accessible by assembling them into user-friendly compilations. Initially these were published as hard copy lists, but since 1997 they have also been made available electronically (see the Plant DNA C-values database http://www.kew.org/cval/homepage.html). Nevertheless, at the Second Plant Genome Size Meeting in 2003, Bennett noted that as many as 1000 DNA C-value estimates were still unpublished and hence unavailable. Scientists were strongly encouraged to communicate such unpublished data. The present work combines the databasing experience of the Kew-based authors with the unpublished C-values produced by Zonneveld to make a large body of valuable genome size data available to the scientific community. METHODS: C-values for angiosperm species, selected primarily for their horticultural interest, were estimated by flow cytometry using the fluorochrome propidium iodide. The data were compiled into a table whose form is similar to previously published lists of DNA amounts by Bennett and colleagues. KEY RESULTS AND CONCLUSIONS: The present work contains C-values for 411 taxa including first values for 308 species not listed previously by Bennett and colleagues. Based on a recent estimate of the global published output of angiosperm DNA C-value data (i.e. 200 first C-value estimates per annum) the present work equals 1.5 years of average global published output; and constitutes over 12 % of the latest 5-year global target set by the Second Plant Genome Size Workshop (see http://www.kew.org/cval/workshopreport.html). Hopefully, the present example will encourage others to unveil further valuable data which otherwise may lie forever unpublished and unavailable for comparative analyses.     

Nuclear DNA amounts in angiosperms: targets, trends and tomorrow

BACKGROUND AND AIMS: The amount of DNA in an unreplicated gametic chromosome complement is known as the C-value and is a key biodiversity character of fundamental significance with many practical and predictive uses. Since 1976, Bennett and colleagues have assembled eight compilations of angiosperm C-values for reference purposes and subsequently these have been pooled into the Angiosperm DNA C-values Database (http://data.kew.org/cvalues/). Since the last compilation was published in 2005, a large amount of data on angiosperm genome size has been published. It is therefore timely to bring these data together into a ninth compilation of DNA amounts. Scope The present work lists DNA C-values for 2221 species from 151 original sources (including first values for 1860 species not listed in previous compilations). Combining these data with those published previously shows that C-values are now available for 6287 angiosperm species. KEY FINDINGS: Analysis of the dataset, which is by far the largest of the nine compilations published since 1976, shows that angiosperm C-values are now being generated at the highest rate since the first genome sizes were estimated in the 1950s. The compilation includes new record holders for the smallest (1C = 0·0648 pg in Genlisea margaretae) and largest (1C = 152·23 pg in Paris japonica) genome sizes so far reported, extending the range encountered in angiosperms to nearly 2400-fold. A review of progress in meeting targets set at the Plant Genome Size meetings shows that although representation for genera, geographical regions and some plant life forms (e.g. island floras and parasitic plants) has improved, progress to increase familial representation is still slow. In terms of technique it is now clear that flow cytometry is soon likely to become the only method available for plant genome size estimations. Fortunately, this has been accompanied by numerous careful studies to improve the quality of data generated using this technique (e.g. design of new buffers, increased awareness and understanding of problems caused by cytosolic inhibitors). It is also clear that although the speed of DNA sequencing continues to rise dramatically with the advent of next-generation and third-generation sequencing technologies, 'complete genome sequencing' projects are still unable to generate accurate plant genome size estimates.     

Evolution of DNA amounts across land plants (embryophyta)

BACKGROUND AND AIMS: DNA C-values in land plants (comprising bryophytes, lycophytes, monilophytes, gymnosperms and angiosperms) vary approximately 1000-fold from approx. 0.11 to 127.4 pg. To understand the evolutionary significance of this huge variation it is essential to evaluate the phylogenetic component. Recent increases in C-value data (e.g. Plant DNA C-values database; release 2.0, January 2003; http://www.rbgkew.org.uk/cval/homepage.html) together with improved consensus of relationships between and within land plant groups makes such an analysis timely. METHODS: Insights into the distribution of C-values in each group of land plants were gained by superimposing available C-value data (4119 angiosperms, 181 gymnosperms, 63 monilophytes, 4 lycophytes and 171 bryophytes) onto phylogenetic trees. To enable ancestral C-values to be reconstructed for clades within land plants, character-state mapping with parsimony and MacClade was also applied. KEY RESULTS AND CONCLUSIONS: Different land plant groups are characterized by different C-value profiles, distribution of C-values and ancestral C-values. For example, the large ( approximately 1000-fold) range yet strongly skewed distribution of C-values in angiosperms contrasts with the very narrow 12-fold range in bryophytes. Further, character-state mapping showed that the ancestral genome sizes of both angiosperms and bryophytes were reconstructed as very small (i.e. < or =1.4 pg) whereas gymnosperms and most branches of monilophytes were reconstructed with intermediate C-values (i.e. >3.5, <14.0 pg). More in-depth analyses provided evidence for several independent increases and decreases in C-values; for example, decreases in Gnetaceae (Gymnosperms) and heterosperous water ferns (monilophytes); increases in Santalales and some monocots (both angiosperms), Pinaceae, Sciadopityaceae and Cephalotaxaceae (Gymnosperms) and possibly in the Psilotaceae + Ophioglossaceae clade (monilophytes). Thus, in agreement with several focused studies within angiosperm families and genera showing that C-values may both increase and decrease, it is apparent that this dynamic pattern of genome size evolution is repeated on a broad scale across land plants.     

Nuclear DNA Amounts in Angiosperms and their Modern Uses--807 New Estimates

The DNA amount in the unreplicated haploid nucleus of an organismis known as its C-value. C-values differ about 1000-fold amongangiosperms and are characteristic of taxa. The data are usedin many biological fields, so they should be easily available.Values for 2802 angiosperm species (1%) were estimated during1950–1997, and five collected lists of C-values were publishedfor reference purposes during 1976–1997. Numbers of newangiosperm C-values published recently remained high, necessitatinga further supplementary list. This paper lists DNA C-valuesfor 807 angiosperm species from 70 original sources, including520 (75.2%) from sources published after 1996, and 691 for speciesnot included in any of the previous five lists. There is a continuingneed to estimate accurate DNA C-values for plant taxa, as shownin a workshop on this biodiversity topic sponsored by Annalsof Botany and held at Kew in 1997. Its key aim was to identifymajor gaps in our knowledge of plant DNA amounts and to recommendtargets and priorities for new work to fill them. A target ofestimating first C-values for the next 1% of angiosperm speciesin 5 years was set. The proportion of such C-values in the presentwork (85.6%) is very high; and the number being published (approx.220 per annum) has never been exceeded. In 1997, C-values werestill unknown for most (68%) families, so a target of completecoverage was set. This paper includes first C-values for 12families, but as less than 2% of such values listed here targetednew families, the need to improve familial representation remains.Copyright 2000 Annals of Botany Company Angiosperm DNA amounts, DNA C-values, nuclear genome sizes, plant DNA database     

Genome downsizing in polyploid plants

All else being equal, polyploids are expected to have larger C-values (amount of DNA in the unreplicated gametic nucleus) than their diploid progenitors, increasing in direct proportion with ploidy. This expectation is observed in some polyploid series, especially those newly formed, but there are examples suggesting that C-values in particular polyploids are less than expected. The availability of the Angiosperm DNA C-values database ( http://www.rbgkew.org.uk/cval/homepage.html ) has allowed this question to be addressed across a broad range of angiosperms and has revealed striking results deviating from expectation: (i) mean 1C DNA amount did not increase in direct proportion with ploidy, and (ii) mean DNA amount per basic genome (calculated by dividing the 2C value by ploidy) tended to decrease with increasing ploidy. These results suggest that loss of DNA following polyploid formation, or genome downsizing, may be a widespread phenomenon of considerable biological significance. Recent advances in our understanding of the molecular events that take place following polyploid formation together with new data on how DNA amounts can both increase and decrease provide some insights into how genome downsizing may take place. The nature of the evolutionary forces that may be driving DNA loss are also discussed.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 651–663.     

First nuclear DNA C-values for 18 eudicot families

BACKGROUND AND AIMS: 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. METHODS: Flow cytometry or Feulgen microdensitometry were used to estimate nuclear DNA C-values, and chromosome counts were obtained where possible. KEY RESULTS: 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. CONCLUSIONS: 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.     

Nuclear DNA Amounts in Angiosperms--583 New Estimates

The amount of DNA in the unreplicated haploid nuclear genome(itsC-value) varies over 600-fold between angiosperm species.Information regarding this character is used in a strikinglywide variety of plant biological fields. Moreover, recent studieshave noted a significant need for more information about thisimportant aspect of genome biodiversity. Bennett and co-authorshave published four collected lists of nuclear DNA amounts inangiosperm species, compiled primarily for reference purposes,including the most recent in 1995 (Annals of Botany76: 113–176).Together they list estimates for over 2500 species which representabout 1% of the global angiosperm flora. Interest in angiospermgenome size has remained high, as shown by the recent publicationof many new estimates, creating a need for a fifth compilation.This paper presents a supplementary list of nuclear DNAC-valuesfrom 37 sources for 471 angiosperm species not listed in theaforementioned compilations, plus additional estimates for 113species already listed by them. It contains estimates for palm,orchid and tropical hardwood species which significantly improvesrepresentation of the global flora. Work is in hand to combinethe genome size data compiled in this and the aforementionedpapers into a unified database, and to present the informationin separate lists, with species in alphabetical and systematicorders, respectively. Meanwhile, the availability of DNAC-valuesfor angiosperm species can be checked on the World Wide Web(http://www.rbgkew.org.uk/cval/database1.html). Angiosperm DNA amounts; DNAC-values; nuclear genome sizes; reference lists; plant DNA database     

Nuclear DNA C-values in 30 species double the familial representation in pteridophytes

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.     

长三角及邻近地区138种草本植物DNA C-值测定及其生物学意义

为了评估DNA C-值和基因组大小(genome size)在植物入侵性评估中的价值,应用流式细胞仪测定了长三角及邻近地区138种草本植物的核DNA含量,其中111种为首次报道。在此基础上比较了不同植物类群这两个值的差异,特别是入侵性与非入侵性植物这两个值的差异。结果表明:(1)138种草本植物平均DNA C-值为1.55 pg,最大者是最小者的37.17倍。127个类群平均基因组大小为1.08 pg,最大者是最小者的34.11倍;(2)统计了菊科(Asteraceae)、禾本科(Poaceae)、石竹科(Caryophyllaceae)、十字花科(Brassicaceae)、玄参科(Scrophulariaceae)、蓼科(Polygonaceae)、唇形科(Labiatae)和伞形科(Umbelliferae)的DNA C-值和基因组大小,发现禾本科植物的这两个值显著地大于其他7个科(P0.01)。单子叶的DNA C-值和基因组极显著地大于双子叶植物(P0.01);(3)杂草比非杂草具有更低的DNA C-值(P0.01)和基因组大小(P0.001);与DNA C-值相比,基因组大小在这两个类群之间的差异更为明显(P0.001),这种现象也体现在菊科植物中。随着基因组(X1)和DNA C-值(X2)由大变小,植物的杂草性(入侵性,Y)由弱变强,两者关系分别符合:Y=2.2334-1.2847 ln(X1)(r=0.4612,P0.01)和Y=2.4421-0.7234 ln(X2)(r=0.2522,P0.01),DNA C-值和基因组大小可以作为植物入侵性评估的一个指标;(4)多倍体杂草的基因组极明显地小于二倍体杂草(P0.01),前者为后者的0.63倍。在非杂草中,多倍体基因组比二倍体的略小,前者仅为后者的0.84倍,差异不显著(P0.5)。菊科植物中多倍体杂草的基因组也显著地小于二倍体杂草(P0.1)。基因组变小和多倍体化相结合,进一步增强了植物的入侵性。在多倍体植物入侵性评估中,基因组大小比DNA C-值更有价值。     

Nuclear DNA content estimates in multicellular green, red and brown algae: phylogenetic considerations

BACKGROUND AND AIMS: Multicellular eukaryotic algae are phylogenetically disparate. Nuclear DNA content estimates have been published for fewer than 1 % of the described species of Chlorophyta, Phaeophyta and Rhodophyta. The present investigation aims to summarize the state of our knowledge and to add substantially to our database of C-values for theses algae. METHODS: The DNA-localizing fluorochrome DAPI (4', 6-diamidino-2-phenylindole) and RBC (chicken erythrocyte) standard were used to estimate 2C values with static microspectrophotometry. KEY RESULTS: 2C DNA contents for 85 species of Chlorophyta range from 0.2-6.1 pg, excluding the highly polyploidy Charales and Desmidiales with DNA contents of up to 39.2 and 20.7 pg, respectively. 2C DNA contents for 111 species of Rhodophyta range from 0.1-2.8 pg, and for 44 species of Phaeophyta range from 0.2-1.8 pg. CONCLUSIONS: New availability of consensus higher-level molecular phylogenies provides a framework for viewing C-value data in a phylogenetic context. Both DNA content ranges and mean values are greater in taxa considered to be basal. It is proposed that the basal, ancestral genome in each algal group was quite small. Both mechanistic and ecological processes are discussed that could have produced the observed C-value ranges.     

First nuclear DNA C-values for 28 angiosperm genera

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.     

First Nuclear DNA C-values for Another 25 Angiosperm Families

Nuclear DNA C-value is an important genomic biodiversity characterwith many uses. An international workshop sponsored by Annalsof Botany and held at the Royal Botanic Gardens, Kew, UK, in1997 identified major gaps in our knowledge of plant DNA C-valuesand recommended targets for new work. Improved taxonomic coveragewas highlighted as a key need for angiosperms, especially atthe familial level. In 1997 C-values were known for only approx.32% of angiosperm families; a goal of complete familial representationby 2002 was recommended. A review published in 2000 (Bennettet al.;Annals of Botany86: 859–909) noted poor progresstowards this aim: of the 691 first C-values for species only12 (1.7%) were for unrepresented families. We began new workto address this in 1999, reporting first DNA C-values for 25angiosperm families in 2001 (Hanson et al.;Annals of Botany87:251–258). Here we report first DNA C-values for a further25 angiosperm families, increasing familial coverage in angiospermsto approx. 45%. Such targeting remains essential to approachthe goal set by the 1997 workshop of familial coverage for angiospermswithin 5 years. The 4C DNA amounts presented here range from0.76 pg (similar toArabidopsis 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 furthersupport for the view that ancestral angiosperms almost certainlyhad small genomes (defined as 1C     

外来入侵植物和本地植物核DNA C-值的比较及其与入侵性的关系

用流式细胞仪测定了8科10属13种外来入侵植物、6种本地植物和1种外来非入侵植物的核DNAC-值。结果表明:作为整体,外来入侵植物的平均核DNAC-值显著低于本地种和外来非入侵种,但对同属不同类型植物进行比较,未发现一致的规律;在4个既包含外来入侵种又包含本地种的属中,泽兰属(Eupatorium)和鬼针草属(Bidens)外来入侵种的核DNAC-值显著低于同属本地种,莲子草属(Alternanthera)的2种外来入侵植物中仅有1个种的核DNAC-值显著低于同属本地种,而草胡椒属(Peperomia)外来入侵种的核DNAC-值显著高于同属本地种;表明核DNAC-值与外来植物入侵性无必然联系。     

Nuclear DNA Amounts in Pteridophytes

DNA amounts (C-value and genome size) are much-used biodiversitycharacters. A workshop held at Kew in 1997 identified majorgaps in our knowledge of plant DNA amounts, recommending targetsfor new work to fill them. Murray reviewed non-angiosperm plantsnoting that representation of pteridophyte species (approx.0.42%) was poor, while locating C-value data for them was verydifficult. The workshop confirmed the need to make data forother groups besides angiosperms accessible for reference purposes.This paper pools DNA C-values for 48 pteridophyte species fromeight original sources into one reference source, and fulfilsa key workshop recommendation for this group. Comparing thesedata shows that nuclear 1C-values in pteridophytes vary approx.1000-fold, from 0.055 pg in Selaginella species to about 55pg in Ophioglossum petiolatum. Genome size estimates for 25pteridophytes vary approx. 200-fold from 0.055 to 10.7 pg, andthe mean genome sizes in diploids and polyploids (5.15 and 4.59pg, respectively) are not significantly different. Wider comparisonsshow that ranges of genome sizes in the major groups of landplants are very different. Those in bryophytes and pteridophytesare narrow compared with those in gymnosperms and angiosperms.The data indicate that the origin of land plants possibly involveda first major increase in genome size in the evolution of vascularplants, while a second such increase occurred later in gymnosperms.C-values for pteridophytes remain very few, but conversely opportunitiesfor new work on them are many. Copyright 2001 Annals of BotanyCompany Pteridophyte DNA amounts, DNA C-values, nuclear genome sizes     

DNA C-values in seven families fill phylogenetic gaps in the basal angiosperms

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.     

Nuclear DNA Amounts in Angiosperms

Bennett and Smith (Philosophical Transactions of the Royal Societyof London B274:227-274; B334: 309-345) and Bennett, Smith andHeslop-Harrison (Proceedings of the Royal Society of London,B216: 179-199) published lists of nuclear DNA amounts estimatedfor 1612 angiosperm species collected from 163 sources datedbetween 1951 and 1986. Subsequently, interest in genome sizein angiosperms and its significance has continued, and manynew DNA estimates were published during 1986-1994. Their inaccessibility,and the flow of enquiries for such information, shows that afurther compilation is needed. This paper presents a supplementarylist of nuclear DNA C-values for 105 sources for 899 angiospermspecies not listed in the above-mentioned compilations, plus284 additional estimates for 208 species already listed by them.The data are assembled primarily for reference purposes, withspecies listed in alphabetical order, rather than by any taxonomicscheme. Some advantages and limitations of flow cytometry, nowincreasingly used to quantify DNA C-values in plants, are reviewed.Recent reports regarding the occurrence and extent of intraspecificvariation in genome size are also discussed. While some examplesare real, others reflect technical shortcomings. Work has begunto combine the genome size data compiled in this and the above-mentionedpapers into a unified data base, and to present the informationin separate lists, with species in alphabetical and systematicorders, respectively. DNA C-values are now known for 1% of theworld's angiosperm flora, but improved representation of taxonomicgroups, geographical regions and plant life forms is urgentlyneeded.Copyright 1995, 1999 Academic Press Angiosperm DNA amounts, DNA C-values, nuclear genome sizes, intraspecific variation, flow cytometry, reference lists, genome size database     

Smallest angiosperm genomes found in lentibulariaceae, with chromosomes of bacterial size

Nuclear holoploid genome sizes (C-values) have been estimated to vary about 800-fold in angiosperms, with the smallest established 1C-value of 157 Mbp recorded in Arabidopsis thaliana. In the highly specialized carnivorous family Lentibulariaceae now three taxa have been found that exhibit significantly lower values: Genlisea margaretae with 63 Mbp, G. aurea with 64 Mbp, and Utricularia gibba with 88 Mbp. The smallest mitotic anaphase chromatids in G. aurea have 2.1 Mbp and are thus of bacterial size (NB: E. coli has ca. 4 Mbp). Several Utricularia species range somewhat lower than A. thaliana or are similar in genome size. The highest 1C-value known from species of Lentibulariaceae was found in Genlisea hispidula with 1510 Mbp, and results in about 24-fold variation for Genlisea and the Lentibulariaceae. Taking into account these new measurements, genome size variation in angiosperms is now almost 2000-fold. Genlisea and Utricularia are plants with terminal positions in the phylogeny of the eudicots, so that the findings are relevant for the understanding of genome miniaturization. Moreover, the Genlisea-Utricularia clade exhibits one of the highest mutational rates in several genomic regions in angiosperms, what may be linked to specialized patterns of genome evolution. Ultrasmall genomes have not been found in Pinguicula, which is the sister group of the Genlisea-Utricularia clade, and which does not show accelerated mutational rates. C-values in Pinguicula varied only 1.7-fold from 487 to 829 Mbp.     

A strong nucleotypic effect on the cell cycle regardless of ploidy level

Background and Aims: In published studies, positive relationships between nucleotypeand the duration of the mitotic cell cycle in angiosperms havebeen reported but the highest number of species analyzed wasapprox. 60. Here an analysis is presented of DNA C-values andcell cycle times in root apical meristems of angiosperms comprising110 measurements, including monocots and eudicots within a settemperature range, and encompassing an approx. 290-fold variationin DNA C-values. Methods: Data for 110 published cell cycle times of seedlings grown attemperatures between 20–25 °C were compared with DNAC-values (58 values for monocots and 52 for eudicots). Regressionanalyses were undertaken for all species, and separately formonocots and eudicots, diploids and polyploids, and annualsand perennials. Cell cycle times were plotted against the nuclearDNA C-values. Key Results: A positive relationship was observed between DNA C-value andcell cycle time for all species and for eudicots and monocotsseparately, regardless of the presence or absence of polyploidvalues. In this sample, among 52 eudicots the maximum cell cyclelength was 18 h, whereas the 58 monocot values ranged from 8–120h. There was a striking additional increase in cell cycle durationin perennial monocots with C-values greater than 25 pg. Indeed,the most powerful relationship between DNA C-value and cellcycle time and the widest range of cell cycle times was in perennialsregardless of ploidy level. Conclusions: DNA replication is identified as a rate limiting step in thecell cycle, the flexibility of DNA replication is explored,and we speculate on how the licensing of initiation points ofDNA replication may be a responsive component of the positivenucleotypic effect of C-value on the duration of the mitoticcell cycle.     

The relationship between nuclear DNA content and leaf strategy in seed plants

BACKGROUND AND AIMS: Species' 2C-values (mass of DNA in G(1) phase 2n nuclei) vary by at least four orders of magnitude among seed plants. The 2C-value has been shown to be co-ordinated with a number of other species traits, and with environmental variables. A prediction that species 2C-values are negatively related to leaf life span (LL) and leaf mass per area (LMA) is tested. These leaf traits are components of a major dimension of ecological variation among plant species. METHODS: Flow cytometry was used to measure the 2C-values for 41 Australian seed plant species, 40 of which were new to the literature. Where possible, LL and LMA data from the global literature were combined with 2C-values from our data set and online C-value databases. KEY RESULTS: Across all species, weak positive relationships were found between 2C-values and both LL and LMA; however, these did not reflect the relationships within either angiosperms or gymnosperms. Across 59 angiosperm species, there were weak negative relationships between 2C-values and both LL (r2 = 0.13, P = 0.005) and LMA (r2 = 0.15, P = 0.002). These relationships were the result of shifts to longer LL and greater LMA in woody compared with herbaceous growth forms, with no relationships present within growth forms. It was not possible to explain a positive relationship between 2C-values and LMA (r2 = 0.30, P = 0.024) across 17 gymnosperm species. The 2C-value was not related to LL or LMA either across species within orders (except for LMA among Pinales), or as radiation divergences in a model phylogeny. CONCLUSIONS: Gymnosperms appear to vary along a spectrum different from angiosperms. Among angiosperms, weak negative cross-species relationships were associated with growth form differences, and traced to a few divergences deep in the model phylogeny. These results suggest that among angiosperms, nuclear DNA content and leaf strategy are unrelated.     

Nuclear DNA variation, chromosome numbers and polyploidy in the endemic and indigenous grass flora of New Zealand

BACKGROUND AND AIMS: Little information is available on DNA C-values for the New Zealand flora. Nearly 85 % of the named species of the native vascular flora are endemic, including 157 species of Poaceae, the second most species-rich plant family in New Zealand. Few C-values have been published for New Zealand native grasses, and chromosome numbers have previously been reported for fewer than half of the species. The aim of this research was to determine C-values and chromosome numbers for most of the endemic and indigenous Poaceae from New Zealand. SCOPE: To analyse DNA C-values from 155 species and chromosome numbers from 55 species of the endemic and indigenous grass flora of New Zealand. KEY RESULTS: The new C-values increase significantly the number of such measurements for Poaceae worldwide. New chromosome numbers were determined from 55 species. Variation in C-value and percentage polyploidy were analysed in relation to plant distribution. No clear relationship could be demonstrated between these variables. CONCLUSIONS: A wide range of C-values was found in the New Zealand endemic and indigenous grasses. This variation can be related to the phylogenetic position of the genera, plants in the BOP (Bambusoideae, Oryzoideae, Pooideae) clade in general having higher C-values than those in the PACC (Panicoideae, Arundinoideae, Chloridoideae + Centothecoideae) clade. Within genera, polyploids typically have smaller genome sizes (C-value divided by ploidy level) than diploids and there is commonly a progressive decrease with increasing ploidy level. The high frequency of polyploidy in the New Zealand grasses was confirmed by our additional counts, with only approximately 10 % being diploid. No clear relationship between C-value, polyploidy and rarity was evident.