Nuclear DNA Content of 26 Orchid (Orchidaceae) Genera with Emphasis onDendrobium

2C DNA content values for 70 orchid species from 26 genera,including 37Dendrobiumspecies from eight taxonomic sections,were analysed using flow cytometry. The resulting nuclear DNAcontent values for species other thanDendrobiumranged from 1.91pg 2C^-1to 15.19 pg 2C^-1nuclei forCadetia tayloriandVanilla phaeantha,respectively.Dendrobiumnuclear DNA content values ranged from1.53 pg 2C^-1to 4.23 pg 2C^-1nuclei forD. cruentumandD. spectabile,respectively. DNA content measurements varied greatly withinDendrobiumsectionsLatouria and Spatulata. Nuclear DNA content values for the sixspecies analysed within Latouria ranged from 1.88 pg 2C^-1nucleiforD. macrophyllumto 4.23 pg 2C^-1nuclei forD. spectabile. NuclearDNA content values for the 16 species analysed within Spatulataranged from 1.69 pg 2C^-1nuclei forD. discolorto 4.05 pg 2C^-1nucleiforD. samoense. The least variation in DNA content was foundwithin the section Phalaenanthe, with nuclear DNA content valuesof 1.79 pg  2C^-1, 1.86 pg 2C^-1and 1.98 pg 2C^-1forD. bigibbum,D.affineandD. phalaenopsis, respectively.Copyright 1998 Annalsof Botany Company Orchidaceae,Dendrobium, flow cytometry, propidium iodide, nuclear DNA, genome size, 2C values.     

Variation in the DNA Content of Glycine Species

Nuclei were isolated from cotyledons of a range of accessionsfrom 14 species of Glycine. These were stained with ethidiumbromide and the relative fluorescence for each genotype wasmeasured by flow cytometry. The DNA content was estimated bycomparison of relative fluorescence with that from nuclei fromseedling leaves of Allium cepa, whose DNA content has been calculatedpreviously by chemical assay. The 4C amounts for diploid Glycineranged from 3.80 to 6.59 pg. Two groups of diploid species appearedfrom the analysis. The first consisted of species with amountsranging from 3.80 to 5.16 pg and included G. canescens (AA),G. argyrea (A₁ A₁), G. clandestina (A²A²), G. microphylla(BB),G. latifolia (B₁B₁), G. tabacina 2n=40 (B²B²), G. tomentella2n=38 (EE) and 2n=40 (DD), G. max and G. soja (GG), G. arenariaand G. latrobeana. A second group had higher DNA contents rangingfrom 5.27 to 6.59 pg, and consisted of G. curvata, G. cyrtoloba(CC), and G. falcata (FF). The polyploid species, G. tabacina2n=80 (AABB, BBB¹B¹), G. tomentella 2n=78 and 2n=80 (AAEE andDDEE, respectively) contained amounts approximating to the sumsof the respective parental diploid species thought to have givenrise to these allotetraploids. Intraspecific variation was detectedin the DNA content of G. canescens. Within the overall distributionof DNA amounts found in A genome species, each genome containeda range of DNA contents specific to that species. This phenomenonwas also detected amongst B genome species.     

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     

Nuclear DNA Content in Twelve Species of Alstroemeria L. and Some of their Hybrids

Nuclear DNA content (2C-value), estimated through flow cytometryusing propidium iodide (PI), was shown to vary from 36.5 pgto 78.9 pg among 29 accessions of 12Alstroemeria species (2n=2x =16). The extremes were found inA. magnifica ssp.magnificaand inA. ligtu ssp.simsii , both belonging to the Chilean speciesgroup. The four Brazilian species exhibited less variation innuclear DNA content (49.8–56.4 pg), than the eight Chileanspecies (36.5–78.9 pg). Nuclear DNA content was positivelycorrelated (r =0.92,n =7,P <0.01) with the total chromosomelength. It was also positively correlated (r =0.85,n =5,P <0.01)with the length of C-bands, when only the Chilean species wereconsidered. When both karyotype parameters, length of non-C-bandedchromosome regions (x) and length of C-bands (y) were determined,it was possible to predict the nuclear DNA content (z) withthe formula z=0.65x +1.31y-0.45 (R ²=0.97,P =0.004). The DAPI fluorescence of most accessions was proportional tothe PI fluorescence (r =0.98,P <0.001), except for one accessionofA. ligtu , that had a relatively high PI/DAPI ratio (1.88).The PI/DAPI ratios of the Brazilian species were lower (1.59–1.67)than those of the Chilean species (1.68–1.88), which mightreflect a difference in base pair composition. Four groups ofspecies could be distinguished on the basis of fluorescencevalues. Diploid interspecific hybrids were shown to have a DNAcontent intermediate to the values of the parents involved.Both the PI and the DAPI fluorescence values of these hybridsapproximated the mid parent values. Tetraploids, derived fromselfing of diploids, had PI and DAPI fluorescence values thatwere twice that of the diploid hybrids. It was possible to distinguishaneuploids from euploids based on fluorescence values. Alstroemeria ; aneuploidy; C-banding; DAPI; evolution; flow cytometry; genome size; geophytes; karyotypes; Inca Lily; nuclear DNA; propidium iodide     

Variation of Nuclear DNA Content in the Biflorus Species of Lonchocarpus (Leguminosae)

This represents the first study of nuclear DNA content in alarge sample (135 spp.) from a tropical arboreal genus, in whicha large proportion of the species were examined (42 spp., 31.1%).Somatic chromosome numbers and 4C-DNA values for 51 taxa ofLonchocarpus are reported. All taxa were diploid with 2 n =22,but their DNA content ranged from 1.92 to 2.86 pg 4C nucleus,corresponding to a 48.95% variation in genome size. In the 74collections studied, no correlation was observed between DNAcontent and habitat altitude. Variation in nuclear DNA contentwas analysed at the level of genus, subgenus, section and subsection.Variation in genome size was also studied within some species,either among widely separated populations or among differentintraspecific taxa. Very little variation in genome size wasdetected between populations, subspecies, and varieties of thesame species. The taxonomic implications of variation in nuclearDNA content are discussed.Copyright 2000 Annals of Botany Company Lonchocarpus (Leguminosae), DNA content, chromosome number.     

Genome Size inAllium: In Quest of Reproducible Data

ComparingAlliumgenome size measurements of different authors,we noticed that the estimates for certain species diverge morestrongly than one would have expected in view of the methodologicaladvantages of the material. As the matter has theoretical significancefor explaining the biological role of genome size variation,we measured, by Feulgen densitometry, 28 species and altogether57 accessions or cultivars. Flow cytometric measurements supplementedthese data. The current hypothesis of a discontinuous and step-wisedistribution of DNA amounts inAlliumseems questionable, as mostof our DNA values did not appear in the corresponding DNA groupas proposed previously. On the other hand, we can confirm thatthere is a significant negative correlation between genome sizeof a species and its first month of flowering, but only in diploids,or in diploids and polyploids if only the basic genome size(2Cxlevel) is considered. We compared our results with thoseof nine other publications. Only 29 of 60 2C values publishedpreviously deviate less than 10% from our data, the others deviatemore strongly, from 0.44- to 1.44-fold. The more comprehensivedata sets of various authors were compared by correlation analysiswith our data. Positive and mostly significant correlationswere seen in all tests, but nevertheless the degree of incongruencebetween studies was unsatisfactory in view of the much betterintra-laboratory reproducibility of the present data. The presentwork highlights the need for generally agreed improvements instandardization and preparative procedures of cytophotometricgenome size determination.Copyright 1999 Annals of Botany Company Allium, genome size, Feulgen densitometry, flow cytometry, discontinuous DNA content variation, nucleotype hypothesis, flowering time, data reproducibility, correlation analysis.     

Nuclear DNA Amounts in Roses

Nuclei isolated from young leaves were stained with propidiumiodide (PI) and their fluorescence intensities were measuredby flow cytometry. The ratio of fluorescence intensities offour calibration standards and 34 roses to an internal standard,parsley (Petroselinum crispum), provided a basis for estimatingthe DNA amounts of P. crispum and rose. The 2C DNA amount ofP. crispum(2 n = 22) was estimated as 4.46 pg (s.d. ±0.08 pg). The 2C DNA amounts of diploid roses (2n = 14) variedbetween subgenera, sections and cultivars, and ranged from 0.78pg (s.d. ± 0.08 pg) in Rosa xanthina and R. sericea(sectionPimpinellifoliae) to 1.29 pg (s.d. ± 0.08 pg) in ‘Félicitéet Perpétue’ (Hybrid Sempervirens). Within eachsection, the DNA amounts of diploid species were similar. Inthe sections Carolinae and Cinnamomeae, DNA amounts were proportionalto ploidy numbers. In the Pimpinellifoliae, DNA amounts of tetraploidswere disproportionately larger than those of diploids whichsuggests that they originated as hybrids with species of sectionswith larger DNA amounts. Ratios of the fluorescence intensitiesof nuclei of roses to P. crispum(internal standard) were alsomeasured using 4',6-diamidino-2-phenylindole (DAPI) which bindspreferentially to AT base pairs. These DAPI ratios were lowerthan, but closely correlated (r² = 0.997) with PI ratios. Fluorescenceintensities of either PI or DAPI-stained nuclei of roses canbe used as rapid indicators of ploidy if variation in the DNAamounts between different taxonomic groups is taken into account.Copyright 2000 Annals of Botany Company Flow cytometry, nuclear DNA amounts, Petroselinum crispum, phenolics, Rosa, roses     

Flag Leaf Anatomy of Triticum and Aegilops Species in Relation to Photosynthetic Rate

Quantitative anatomical and other measurements were made onfully expanded flag leaves of a series of diploid, tetraploidand hexaploid Triticum and Aegilops species, and photosyntheticrates per unit leaf area were measured at light saturation (P_max). Diploids had the highest P_max, hexaploids the lowest with tetraploidsbeing intermediate. The anatomical features of tetraploids andhexaploids were generally similar, but different from the diploids.The diploids had thinner leaves with less dry matter and chlorophyllper unit area. The surface area of the mesophyll cells per unitvolume of mesophyll tissue was similar for all ploidy levels,as was the ratio mesophyil cell surface area per unit leaf area.It is argued that while these anatomical features are unlikelyto account for the observed variation in Pmax, it is possiblethat other structural factors with which they are correlatedmay causally influence P_max. One such feature is the averagediffusion path length from the plasmalemma at the cell surfaceto the sites of carboxylation. Anatomy, photosynthesis, mesophyll, cell size, Triticum, Aegilops, polyploidy     

The dynamic ups and downs of genome size evolution in Brassicaceae

Crucifers (Brassicaceae, Cruciferae) are a large family comprisingsome 338 genera and c. 3,700 species. The family includes importantcrops as well as several model species in various fields ofplant research. This paper reports new genome size (GS) datafor more than 100 cruciferous species in addition to previouslypublished C-values (the DNA amount in the unreplicated gameticnuclei) to give a data set comprising 185 Brassicaceae taxa,including all but 1 of the 25 tribes currently recognized. Evolutionof GS was analyzed within a phylogenetic framework based ongene trees built from five data sets (matK, chs, adh, trnLF,and ITS). Despite the 16.2-fold variation across the family,most Brassicaceae species are characterized by very small genomeswith a mean 1C-value of 0.63 pg. The ancestral genome size (ancGS)for Brassicaceae was reconstructed as ^anc1C = 0.50 pg. Approximately50% of crucifer taxa analyzed showed a decrease in GS comparedwith the ancGS. The remaining species showed an increase inGS although this was generally moderate, with significant increasesin C-value found only in the tribes Anchonieae and Physarieae.Using statistical approaches to analyze GS, evolutionary gainsor losses in GS were seen to have accumulated disproportionatelyfaster within longer branches. However, we also found that GShas not changed substantially through time and most likely evolvespassively (i.e., a tempo that cannot be distinguished betweenneutral evolution and weak forms of selection). The data revealan apparent paradox between the narrow range of small GSs overlong evolutionary time periods despite evidence of dynamic genomicprocesses that have the potential to lead to genome obesity(e.g., transposable element amplification and polyploidy). Toresolve this, it is suggested that mechanisms to suppress amplificationand to eliminate amplified DNA must be active in Brassicaceaealthough their control and mode of operation are still poorlyunderstood.     

Nuclear DNA Amounts in Palms (Arecaceae)

Nuclear DNA amounts are reported for 83 species and 53 genera of palms, covering all of the six subfamilies. 4C DNA contents range between 3.89 and 55.62 pg in diploids, showing an approximate 14.3-fold variation in genome size. Polyploids have DNA contents of up to 156.40 pg/4c which demonstrates a 40.2-fold variation. Diploids with high DNA contents occur in three subfamilies of palms (Coryphoideae, Calamoideae, Arecoideae), and seem to be further restricted to particular tribes or subtribes (Thrinacinae, Borasseae, Lepidocaryeae, Caryoteae, some subtribes of Areceae). Palms from the subfamilies Nypoideae and Phytelephantoideae have the lowest DNA amounts, followed by the Phoeniceae and the Corypheae: Livistoninae from the subfamily Coryphoideae. Although DNA amounts in some genera and subtribes are usually constant, e.g., in Phoenix, Phytelephas, the Livistoninae, Dypsidinae, diploid Butiinae), considerable variation occurs at the diploid level in some large and apparently actively evolving genera such as Chamaedorea, Pinanga, Cenoma and possibly Bactris. Formaldehyde fixation is recommended for palms, as conventional ethanol-acetic acid fixation has proved to be unsuitable for DNA estimation of Feulgen-stained nuclei by microdensitometry, since it can lead to errors up to 2.5-fold in extent. Chromosome counts are reported for 72 of the species studied, of which 42 are new.     

EVOLUTIONARY STUDIES OF ATRIPLEX: CHROMOSOME RACES OF A. CONFERTIFOLIA (SHADSCALE)

Atriplex confertifolia (Torr. and Frem.) S. Wats., a species endemic to western United States, occurs as 2n, 4n, 6n, 8n and 10n chromosome races. In the Great Basin, diploids occur altitudinally above the upper levels of Pleistocene lakes; the polyploids are in valley bottoms and sides. Diploids are larger in all respects than tetraploids, hexaploids, and octoploids. Decaploids are the most robust of all. Diploids can be distinguished in early seedling stages by having broader leaves and shorter internodes than polyploids. Polyploid plants are currently produced sporadically in natural populations and appear to be easily generated by unreduced gametes. Most polyploid populations in the Great Basin apparently arose recently and erupted into extensive stands because of the sudden availability of large, relatively uniform domains provided by the disappearance of Pleistocene lakes.     

Genetic variation and conservation of Changnienia amoena, an endangered orchid endemic to China

Nuclear DNA content (2C) is used as a new criterion to investigate nearly all species of the genus Nerine Herb. The species have the same chromosome number (2n = 2x = 22), with the exception of three triploid plants found. The nuclear DNA content of the diploids, as measured by flow cytometry with propidium iodide, is demonstrated to range from 18.0–35.3 pg. This implies that the largest genome contains roughly 2 × 10¹⁰ more base pairs than the smallest. The species, arranged according to increasing genome size, fell apart in three groups if growth cycle and leaf width were also considered. A narrow-leafed, evergreen group with a DNA content between 18.0 and 24.6 pg contains thirteen species, a broad-leaved winter growing group with four species has a DNA content from 25.3–26.2 pg and a broad-leafed summer growing group has a DNA content of 26.8–35.3 pg and contains six species. If the presence of filament appendages and hairiness of the pedicels were also considered, the thirteen evergreen species could be further divided into a group without filament appendages or hairy pedicels with a DNA content of 18.0–18.7 pg. A second group without filament appendages but with hairy pedicels had a DNA content of 19.7–22.3 pg. And a third group with both filament appendages and hairy pedicels had a DNA content of 22.0–24.6 pg. The exception is N. marincowitzii that, despite a low DNA content and narrow leaves is summer growing. The broad-leafed group is further characterised by the absence of filament appendages and the absence of strongly hairy pedicels. The exception here is N. pusilla that, despite a high DNA content, has narrow leaves and minutely hairy pedicels. Nuclear DNA content as measured by flow cytometry is shown to be relevant to throw new light on the relationships between Nerine species.     

Quantitative nuclear DNA changes inEleusine (Gramineae)

2C nuclear DNA amounts were determined in 30 collections belonging to 10 species ofEleusine. About a 2.5-fold variation in genome size is evident in the genus. The 2C DNA amount in the diploid species ranged from 2.50 pg inE. verticillata to 3.35 pg inE. intermedia. In contrast, the tetraploid species showed a range from 4.95 pg inE. africana to 6.13 pg inE. floccifolia. At intraspecific level 10 collections ofE. coracana, 6 ofE. indica, 4 ofE. africana, 2 ofE. tristachya, and 2 ofE. kigeziensis did not show any significant variation. However, 2 collections ofE. floccifolia, connected with polyploidy, displayed about 90% variation. Polyploid species showed approximately double the genome size of that of their corresponding diploids. An evolutionary increase in DNA amount is evident inE. coracana during the course of its origin and domestication fromE. africana.     

The Close Relationship Between the A and B Genomes in Avena L. (Poaceae) Determined by Molecular Cytogenetic Analysis of Total Genomic, Tandemly and Dispersed Repetitive DNA Sequences

The genusAvena L. (Poaceae) consists of diploid, tetraploid,and hexaploid species, with the B genome known only in tetraploidspecies and the D genome in the hexaploid species. DNA:DNAinsitu hybridization, using total genomic DNA from diploidAvenastrigosa Schreb. (A_sgenome) as a probe, labelled all 28 chromosomesof the AB tetraploidAvena vaviloviana (Malz.) Mordv. stronglyand uniformly, revealing the close relationship between thesetwo genomes. Comparison of patterns of size-separated DNA restrictionfragments between the diploidA. strigosa and the tetraploidA.vaviloviana , using 32 different restriction enzymes, revealedno differences. Southern hybridization using total AB genomicDNA as a probe also gave no differences in banding patternsbetween the two genomes, even when a large excess of A genomicDNA was used as a block. From anA. vaviloviana genomic library,1800 colonies were blotted and probed sequentially with A andAB genomic DNA, but no colony was identified to be B genomespecific. DNA digests of AB genome tetraploids with restrictionenzymeHae III gave a strong band at 4.2 kb. Clone pAbKB3, derivedfrom the 4.2 kb band, was found to be part of aTy1-copia -likeretrotransposon present in A and B genome chromosomes. ClonedrRNA genes were used forin situ hybridization and showed thatdiploidA. strigosa has four major sites for 18S-25S rDNA andtwo pairs of sites for 5S rDNA (pairs on the same satellitedchromosome, on different chromosome arms), while 4xA. vavilovianahas eight major sites for 18S-25S rDNA and four pairs of sitesfor 5S rDNA (pairs on the same satellited chromosome, on differentchromosome arms). A repetitive sequence from rye pSc119.2, showeddispersed hybridization, while the telomeric sequence in clonepLT11 hybridized to telomeres. Again no discrimination was possiblebetween A and B genome chromosomes. The molecular similaritiesbetween the diploidA. strigosa and thebarbata group tetraploidsclearly indicate that thebarbata group of tetraploids arosefrom A_sdiploids through autotetraploidization. Avena ; evolution; repetitive sequences; in situ hybridization; retrotransposons; genome organization     

Nuclear DNA C-values Complete Familial Representation in Gymnosperms

The gymnosperms are a monophyletic yet diverse group of woodytrees with approx. 730 extant species in 17 families. A recentsurvey showed that DNA C-values were available for approx. 16%of species, but for only 12 of the 17 families. This paper completesfamilial representation reporting first C-values for the fiveremaining families: Boweniaceae, Stangeriaceae, Welwitschiaceae,Cephalotaxaceae and Sciadopityaceae. C-values for nine Ephedraand two Gnetum species are also reported. C-values are now availablefor 152 (21%) species. Analysis confirms that gymnosperms arecharacterized by larger C-values than angiosperms (modal 1Cof gymnosperms = 15.8 pg compared with 0.6 pg in angiosperms)although the range (1C = 2.25–32.20 pg) is smaller thanthat in angiosperms (1C = 0.05–127.4 pg). Given completefamilial coverage for C-values and increasing consensus in gymnospermphylogeny, the phylogenetic component of C-value variation wasalso investigated by comparing the two datasets. This analysisrevealed that ancestral gymnosperms (represented by cycads and/orGinkgo; mean genome size = 14.71 pg) probably had larger genomes thanancestral angiosperms. Copyright 2001 Annals of Botany Company Gymnosperm DNA amounts, C-values, phylogeny, ancestral genome size, Cycadales, Ginkgo, Gnetales, conifers, Pinaceae     

Comparison of four nuclear isolation buffers for plant DNA flow cytometry

• Background and Aims DNA flow cytometry requires preparationof suspensions of intact nuclei, which are stained using a DNA-specificfluorochrome prior to analysis. Various buffer formulas weredeveloped to preserve nuclear integrity, protect DNA from degradationand facilitate its stoichiometric staining. Although nuclearisolation buffers differ considerably in chemical composition,no systematic comparison of their performance has been madeuntil now. This knowledge is required to select the appropriatebuffer for a given species and tissue. • Methods Four common lysis buffers (Galbraith's, LB01,Otto's and Tris.MgCl₂) were used to prepare samples from leaftissues of seven plant species (Sedum burrito, Oxalis pes-caprae,Lycopersicon esculentum, Celtis australis, Pisum sativum, Festucarothmaleri and Vicia faba). The species were selected to covera wide range of genome sizes (1·30–26·90pg per 2C DNA) and a variety of leaf tissue types. The followingparameters were assessed: forward (FS) and side (SS) light scatters,fluorescence of propidium iodide-stained nuclei, coefficientof variation of DNA peaks, presence of debris background andthe number of nuclei released from sample tissue. The experimentswere performed independently by two operators and repeated onthree different days. • Key Results Clear differences among buffers were observed.With the exception of O. pes-caprae, any buffer provided acceptableresults for all species. LB01 and Otto's were generally thebest buffers, with Otto's buffer providing better results inspecies with low DNA content. Galbraith's buffer led to satisfactoryresults and Tris.MgCl₂ was generally the worst, although ityielded the best histograms in C. australis. A combined analysisof FS and SS provided a ‘fingerprint’ for each buffer.The variation between days was more significant than the variationbetween operators. • Conclusions Each lysis buffer tested responded to a specificproblem differently and none of the buffers worked best withall species. These results expand our knowledge on nuclear isolationbuffers and will facilitate selection of the most appropriatebuffer depending on species, tissue type and the presence ofcytosolic compounds interfering with DNA staining.     

Taxonomic implications of genome size for all species of the genus Gasteria Duval (Aloaceae)

Nuclear DNA content (2C) is used as a new criterion to investigate all species of the genus Gasteria Duval including the three recently described species Gasteria polita van Jaarsv., G. pendulifolia van Jaarsv. and G. glauca van Jaarsv.. The 122 accessions investigated have the same chromosome number (2n=2x=14), with exception of three tetraploid plants found. The nuclear DNA content of the diploids, as measured by flow cytometry with Propidium Iodide, is demonstrated to range from 32.8–43.2 pg. This implies that the largest genome contains roughly 10¹⁰ more base pairs than the smallest. Based on DNA content the species could be divided in five groups: G. rawlinsonii Oberm. with 32.8 pg, 13 mostly inland species with 34.3–36.0 pg, five coastal species with 36.5–39.0 pg and Gasteria batesiana Rowley with 43.2 pg. The thirteen species with 34.3–36.0 pg could be divided further, in a group of eight species occupying mainly very restricted areas with 34.3–35.1 pg and a second group of five species with 35.2–36.0 pg mainly occupying large areas. These five groups did not coincide very well with the two sections and four series of Gasteria based on a cladistic analysis by van Jaarsveld et al. (1994). Based on its long leafy branches, location in the centre of Gasteria species distribution and its by far lowest DNA content, G. rawlinsonii might be the most primitive member of the genus. Nuclear DNA content as measured by flow cytometry is shown to be relevant to provide additional information on the relationships between Gasteria species.     

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     

A comparative study of the mitochondrial genome organization in in vitro cultures of diploid, tetraploid, and hexaploid Triticum species

Southern-blot hybridizations of total DNA to mitochondrial DNA (mtDNA) probes were used to investigate the extent of mtDNA variability in cultures derived from immature embryos of diploid (Triticum monococcum, genomic formula: AA, T. tauschii, genomic formula: DD), allotetraploid (T. durum cv Creso, genomic formula: AABB), and allohexaploid (T. aestivum, genomic formula: AABBDD) wheat species. Similar distinct changes in mtDNA organization were observed in in vitro cultures of the derived tetraploid and the hexaploid species with related genomes. The tetraploid and hexaploid species share the B genome and mtDNA variability in in vitro culture is known to be under nuclear control. These results suggest that a study of B genome diploids and other polyploid combinations would now shed light on whether or not mtDNA variability in tissue cultures is under B-genome control.     

Genome size and polyploidy variation in the tropical hardwood genusTerminalia (Combretaceae)

Chromosome complements and 2C DNA amounts of six species ofTerminalia have been studied.Terminalia oliveri, T. myriocarpa andT. arjuna are diploid (2n = 24),T. chebula andT. bellirica are tetraploid (2n = 48),T. muelleri shows a triploid number (2n = 36). Two well demarcated groups of species are recognizable on the basis of chromosome length and 2C DNA values which range from 3.60 pg (T. oliveri) to 12.80 pg (T. bellirica) showing a 3.5-fold difference. Differences of DNA per basic genome or per chromosome are greatest (1.97-fold) betweenT. oliveri andT. arjuna. Two species groups (1)T. oliveri andT. chebula, and (2)T. myriocarpa, T. arjuna, T. muelleri, T. bellirica, therefore are well differentiated by DNA per basic genome, irrespective of polyploidy. The mean values of the two groups are 1.81 pg and 3.34 pg, respectively, showing a 1.84-fold difference. Within diploids and tetraploids there is 1.97-fold and 1.76-fold variation, respectively.