Cytological Analysis of Seedling Roots, Transformed Root Cultures and Roots Regenerated from Callus of Swainsona galegifolia (Andr.) R. Br.

The stability of chromosome number was investigated in culturesof roots from Swainsona galegifolia. Roots from germinated seedsor plants grown in vitro when cultured in liquid medium howed90% or more cells with the diploid number of 2n = 32. The remainingcells showed aneuploidy mostly below 32. The stability of chromosomenumbers was not affected by transformation with Agrobacteriumrhizogenes although when roots were transformed with A. rhizogenesLB 9042 the range of chromosome numbers in the few aneuploidcells present was higher than in roots for which strain A4 wasused. In contrast, roots regenerated from callus had only 15%of cells with 2n = 32 and showed a modal number of 18. Six rootcultures established from individual roots regenerated fromcallus showed a wide variation in number (8–83). Fivecultures had a modal number around 18, the sixth, a modal numberof 39 which is above the diploid number. The implication ofthe results for the production of secondary metabolites fromroot culture is discussed. Key words: Agrobacterium rhizogenes, callus cultures, chromosome number, root cultures, Swainsona galegifolia     

Cytoevolution, Phylogeny and Taxonomy in Epacridaceae

Chromosome numbers in Epacridaceae were collated from variousauthors and superimposed on to recent cladograms for the family.The results strongly indicate that reduction in chromosome numberoccurs with evolutionary advancement. Thus Epacridaceae, incommon with ‘Ericaceaesens. strict .’ and ‘Vacciniaceaesens.strict. ’, has evolved from a primitive karyotype of atleastx =12 and probablyx =13. This conclusion dispels earlierpaleopolyploid models based on a primitivex =6 in the family.Other aspects of cytoevolution, such as chromosome number asa generic character especially in cytologically advanced generaof the Styphelieae, are discussed. Cytoevolution; cladistic models; primitive character states for chromosome number; dysploid falls; cytotaxonomy; Epacridaceae; Richeoideae; Epacridoideae; Epacrideae; Styphelieae; Ericaceae     

COMPARATIVE ANALYSIS OF KARYOTYPES AND NUCLEOLAR ORGANIZER REGIONS IN DIFFERENT POPULATIONS OF MYTILUS TROSSULUS, MYTILUS EDULIS AND MYTILUS GALLOPROVINCIALIS

The cylotaxonomical characteristics of Mytilus tros-sulus, M.edulis and M. galloprovincialis were studied using karyometricanalysis and silver staining. The karyotype of M. trossulus,reported here for the first time, consists of six metacentricand eight submetacentric-subtelocentric chromosome pairs. Theoccurrence of five metacentric chromosome pairs in M. galloprovincialisdifferentiates this taxon from M. trossulus and M. edulis whichboth have six meta-centrics. The number of submetacentric tosubtelo-centric chromosome pairs was variable between populationsand between taxa. We suggest that this variability has arisenfrom differential chromosome condensation rather than from structuralchange. Intercomparison of chromosome relative length showedstrong similarity among the three taxa. Chromosomal nucleolarorganizer regions (NORs) were identically located on two submetacentric-subtelocentricchromosome pairs in all three taxa. However, M. trossulus showeda characteristic difference in the occurrence of NORs on onemetacentric pair, which was absent in M. galloprovincialis andM. edulis. Variability in the number of NORs per cell was observedin all populations studied. We conclude that the three taxaof Mytilus studied here cannot be differentiated by asinglekaryological character, but that a combination of karyologicalcharacters is virtually diagnostic ^* To whom correspondence should be sent (Received 24 January 1994; accepted 9 March 1994)     

Karyotype diversification and evolution in diploid and polyploid South American Hypochaeris (Asteraceae) inferred from rDNA localization and genetic fingerprint data

Background and Aims: Changes in chromosome structure and number play an importantrole in plant evolution. A system well-suited to studying differentmodes of chromosome evolution is the genus Hypochaeris (Asteraceae)with its centre of species' diversity in South America. AllSouth American species uniformly have a chromosome base numberof x = 4 combined with variation in rDNA number and distribution,and a high frequency of polyploidy. The aim of this paper isto assess directions and mechanisms of karyotype evolution inSouth American species by interpreting both newly obtained andprevious data concerning rDNA localization in a phylogeneticcontext. Methods: Eleven Hypochaeris species from 18 populations were studiedusing fluorescence in situ hybridization (FISH) with 35S and5S rDNA probes. A phylogenetic framework was established fromneighbour-net analysis of amplified fragment length polymorphism(AFLP) fingerprint data. Key Results: A single 5S rDNA locus is invariably found on the short armof chromosome 2. Using 35S rDNA loci, based on number (one ortwo) and localization (interstitial on the long arm of chromosome2, but sometimes lacking, and terminal or interstitial on theshort arm of chromosome 3, only very rarely lacking), sevenkaryotype groups can be distinguished; five of these includepolyploids. Karyotype groups with more than one species do notform monophyletic groups. Conclusions: Early evolution of Hypochaeris in South America was characterizedby considerable karyotype differentiation resulting from independentderivations from an ancestral karyotype. There was marked diversificationwith respect to the position and evolution of the 35S rDNA locuson chromosome 3, probably involving inversions and/or transpositions,and on chromosome 2 (rarely 3) concerning inactivation and loss.Among these different karyotype assemblages, the apargioidesgroup and its derivatives constitute by far the majority ofspecies.     

Widespread Chromosome Variation in the Endangered Grassland Forb Rutidosis leptorrhynchoides F. Muell. (Asteraceae: Gnaphalieae)

Rutidosis leptorrhynchoides is an endangered plant endemic tosoutheastern Australia. Chromosome analysis of 19 of the 24known populations of the species has identified 17 differentchromosome variants or cytotypes. The most common cytotypesare a diploid and a tetraploid based on x = 11, and triploidand hexaploid plants with this basic number were also observed.Diploids, triploids and tetraploids based on a second basicnumber ofx = 13 were also seen. Plants with 2 n = 24 were shownto be hybrids between diploids with the two different basicnumbers. Meiotic chromosome pairing analysis of the plants with2n = 24 showed a maximum of two trivalents indicating the presenceof extra copies of one pair of large and one pair of small chromosomesin the 2 n = 26 plants. In addition, a number of different aneuploidsof the 2 n = 22 and 2 n = 44 races were found and many of thesealso showed structural chromosomal variation. The distributionof the two main chromosome races is disjunct with the tetraploidsconfined to southern Victoria. To avoid dysgenic effects, futurere-establishment efforts for this species should avoid mixingseed from different chromosome races. Copyright 2001 Annalsof Botany Company Aneuploidy, conservation genetics, karyotypes, meiosis, polyploidy     

Relationships of the Ethiopian Cereal T'ef (Eragrostis tef (Zucc.) Trotter): Evidence from Morphology and Chromosome Number

The relationships of the cereal Eragrostis tef (Gramineae: Eragrostoideae)have been investigated. Nine species are closely related toT'ef on morphological grounds. Their chromosome numbers arereported. E. pilosa and some of the E. cilianensis complex areclosest to E. tef. These taxa may be useful sources of genesfor T'ef improvement. Ethiopian cereal, T'ef, Eragrostis, Gramineae: Eragrostoideae, chromosome number, poly-ploidy, improvement     

Karyotype, DNA Content and Meiotic Behaviour in Five South American Species ofVicia(Fabaceae)

This paper presents the karyotype, DNA content and meiotic behaviourof five species ofViciafrom Argentina (V. macrogramineaBurk.,V.gramineaSM.,V. epetiolarisBurk.,V. pampicolaBurk. andV. nanaVog.).All the species have the same chromosome number and karyotypeformula (2n=14; 6m+4st+4t). Each species, however, displaysa characteristic number and position of the nucleolar organizerregion (NOR) and different sizes of the respective satellites,confirmed by Ag-NOR banding. Moreover, significant differenceswere found in the total chromosome volume (TCV) and DNA contentof the species. Positive correlations between DNA content andTCV, and between DNA content and type of life cycle were alsofound. TCV and DNA content are lower inV. nana(annual) and higherinV. macrograminea(biennial–perennial). The material displayedmarked karyotypic orthoselection, with similar karyotypes inall studied species, even when the overall chromosome size varied.Evolutionary changes in DNA amount are proportional to the relativelength of each chromosome arm, maintaining karyotypic uniformity.Significant differences were found between the meiotic behaviourofV. gramineaand that of the other species.V. gramineahas alower frequency of ring bivalents and chiasmata per cell, andalso has a lower interstitial chiasma frequency. In general,the results are congruent with the morphological data reportedfor these species.Copyright 1998 Annals of Botany Company. Viciaspecies, karyotype, orthoselection, nuclear DNA content, NOR banding, meiotic behaviour.     

Differential Accumulation of Heterochromatin as a Cause for Karyotype Variation in Phalaenopsis Orchids

Karyotypes of nine Phalaenopsis species and the closely relatedDoritis pulcherrima were compared based on Feulgen- and DAPI-stainedsomatic metaphase chromosomes prepared from root tips. All specieshad the same chromosome number (2n = 2x = 38), but their karyotypesdiffered markedly in absolute chromosome size, relative chromosomesize, and the position of the centromere. Both genome size andthe amount of constitutive heterochromatin (CH) varied widelyamong the species studied, and there was a positive correlationbetween these two parameters. The distribution of CH in thegenomes was non-random: one or both arms of long chromosomesusually possessed large blocks of CH, while the small chromosomescontained little or no CH. DAPI-staining revealed that mostCH regions are rich in AT base pairs. We suggest that differentialaccumulation of CH is a major cause for karyotype variationin Phalaenopsis orchids. Copyright 2001 Annals of Botany Company Phalaenopsis, Doritis pulcherrima, karyotype differentiation, constitutive heterochromatin, total chromosome volume, nuclear DNA content     

High-Resolution Mapping of Ribosomal Protein Genes to Human Chromosome 19

In a systematic effort for mapping of all the human ribosomalprotein (rp) genes, we have found that an unusually large number(12) of rp genes are present on chromosome 19 and subsequentlydetermined their locations on the chromosome by a radiation-hybridprocedure. For this, we isolated cosmid clones correspondingto each gene and placed nine of them on a metric physical mapof chromosome 19. Although most genes are scattered over thechromosome, we found three genes are clustered in a 0.6-Mb regionat 19q13.3 and two of them, RPL13A and RPS11, within a singlecosmid only 4.3 kb apart. To explore a possible relationshipbetween rp gene defects and human disease, we compared map positionsof the rpgenes and disease loci on chromosome 19, which ledus to find RPS9 gene in the same interval as the gene for retinitispigmentosa 11. The disease locus has previously been mappedto the 6-cM interval at 19q13.4 between markers D19S572 andD19S926, which corresponds to less than 2-Mb region on the metricphysical map. We mapped RPS9 about 800 kb distal to D19S572.     

Callus Induction and Plant Regeneration from Barley Mature Embryos

Callus cultures were induced starting from excised mature embryosin spring barley, Hordeum vulgare cv Maxima On a medium containinga high level of auxin, a first primary callus was induced whichwas friable, unorganized and capable of direct plant regenerationin the tested conditions This callus type was characterizedby fast growth and high variability in chromosome number Subsequently,a secondary callus type arose from the primary calli subculturedon the same medium in the light This callus type was white andcompact and consisted predominantly of diploid cells When transferredto hormone-free medium it gave rise to green shoots Completerooting of the shoots was achieved on half-strength basal mediumfollowed by exposure to higher light intensity Regenerated plantletscould then be transferred directly into soil without sufferingany loss in vitality Although showing different degrees in morphologicalvariability, they all maintained the diploid chromosome number Hordeum vulgare L, spring barley, morphogenic calli, organogenesis     

Ontogenesis of Tannin Coenocytes in Sambucus racemosa L. I. Development of the Coenocytes from Mononucleate Tannin Cells

Tannin coenocytes in shoots of Sambucus racemosa L. developfrom mono-nucleate tannin cells which can be distinguished amongthe cells of the first internode, and which keep on growing.After karyokinesis without cytokinesis bi-nucleate tannin cellsoccur which yield a synchronous karyokinesis leading to 4 nucleiin the tube. The number of nuclei in the coenocyte is 2ⁿ wheren equals the number of karyokineses that have occurred. Sometimesthe number of nuclei is different and one nucleus is bigeerthan the rest indicating that a previous fusion of nuclei hasoccurred. The distribution of nuclei in the coenocyte supportsthe possibility of fusion of chromosome sets at the moment ofnuclear envelope dispersion. Sambucus racemosa L., coenocytes, synchronous karyokinesis, development     

GENETIC AND MORPHOLOGICAL VARIATION OF POPULATIONS BELONGING TO THE BULINUS TRUNCATUS/TROPICUS COMPLEX (GASTROPODA; PLANORBIDAE) IN SOUTH WESTERN ZIMBABWE

Aquatic snails from south western Zimbabwe belonging to theBulinus trunscatus/tropicus complex vary widely in shell formsuggesting that more than one taxon could be present. This possibilitywas investigated by making observations on snail samples from13 populations from the Plumtree area, in respect of allozymevariation (5 polymorphic loci), shell morphology (9 variables),copulatory organ and chromosome number. Comparative data wereobtained from snails from north western Zimbabwe identifieddefinitely as B. tropicus. Analysis of the genetic structurerevealed a high degree of polymorphism (P) ranging from 0.29–0.80among populations from Plumtree and expected heterozygosity(H_e) from 0.02–0.22. No enzymatic diagnostic loci werefound which could differentiate the different morphs or populationsand discriminant function analysis on the morphological datashowed an overlap of morphs among populations. Snails analyzedfor chromosome number were all diploid (2n = 36). Snails exposedto Schistosoma haematobium mira-cidia were all refractory. Thisinformation supports the view of a single species, B. tropicus,which is differentiated due to migration barriers and whereenvironmental variables might be implicated in the morphometricdivergence. (Received 31 July 1995; accepted 15 January 1998)     

Chromosome Number of Laminaria digitata Lamour

An investigation of the chromosome number of Laminaria digitataLamour has revealed the diploid complement to be 16. Endomitoticchromosome multiplication has been observed. A similar investigationby Magne has shown the diploid number of chromosomes to be 26in Laminaria flexicaulis Le Jolis and raises the taxonomicalquestion whether these two names can be regarded as synonymsas at present used or covering distant species.     

Cloning and Mapping of Telomere-Associated Sequences from Rice

We have isolated three telomere-associated sequences from riceusing cassette-ligation-mediated polymerase chain reaction (PCR).Each of the obtained clones hybridized to the terminal of oneor several rice chromosome arms. The telomeres recognized bythe clones displayed a high level of polymorphism between tworice varieties, Nipponbare (a japonica variety) and Kasalath(an indica variety). Variability in the chromosome termini wasalso detected among individual F₂ progeny plants, which werederived from a cross between the two rice varieties. One clonecontaining telomere-associated sequences was located to oneend of chromosome 5, and another clone to one end of chromosome11. For another clone, non-allelic segregation of polymorphichybridization bands was observed between japonica and indicarice; this clone was mapped to one end of chromosome 12 in japonicaand to one end of chromosome 11 in indica rice. This indicatesan exchange of termini between nonhomologous chromosomes.     

Karyological Anatomy of Fibre Development in the Leaves of Agave americana L. var. marginata alba Trel.

From a study of 100 metaphase plates in root-tip squashes and75 fibre-cells in leaf-base squashes, it is found that the chromosomenumber, although having an irregular type of variation, commonlytend to occur as multiples of 15, the haploid number. In developingfibre-cells the tendency of complete endomitosis (resultingin 2n, 4n, and 8n numbers) is stronger than the partial endomitosis(resulting in 5n, 6n, 7n, etc.). Nuclear volumes of fibre-cellsalso roughly correspond to 2K, 4K, and 8K. Significant linearcorrelations between chromosome number and nuclear volume andbetween nuclear volume and fibre-cell volume has been obtained.Thus the development and differentiation of fibres involve completeand partial endomitoses, accompanied by somatic non-disjunctionphenomena.     

Functional and Structural Chromosome Analyses in Autotetraploid Silene latifolia

Recent immunocytological and molecular data show that heterochromaticnuclear regions, both constitutive and facultative, are modifieddifferently (cytosine hypermethylation and histone hypoacetylation)and late replicating, when compared to euchromatin. Intrusiveand/or additive (supernumerary) DNA sequences are often functionallysilenced; this is accompanied by their heterochromatinization.In this work we present a number of karyological studies onautotetraploid female cells of Silene latifolia (syn. Melandriumalbum). Immunofluorescence analyses do not indicate any globaldifferences in DNA methylation, histone H4 acetylation, andchromosome replication patterns which could arise as a consequenceof the duplication of the whole chromosome set of the originaldiploid genome. Similarly, the number of silver-positive nucleoliroughly correlates to the ploidy level. Early replication andH4 hyperacetylation have been detected at all subterminal chromosomeregions. This, together with cDNA in situ hybridization patterns,indicates the localization of gene-rich regions. DNA methylationand chromosome replication patterns, but not histone H4 acetylation,show differences among the four X chromosomes present: one tothree X chromosomes were observed as hypermethylated and/orlate replicating. Taken together, the data demonstrate thatthere is no overall silencing of the additional two sets ofautosomes in the tetraploid cells, but the X chromosomes couldbe subject to an irregular dosage compensation. Copyright 1999Annals of Botany Company DNA methylation, histone acetylation, polyploidy, replication patterns, sex chromosomes, Silene latifolia (syn.Melandrium album ).     

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.     

Complete Genomic Structure of the Bloom-forming Toxic Cyanobacterium Microcystis aeruginosa NIES-843

The nucleotide sequence of the complete genome of a cyanobacterium,Microcystis aeruginosa NIES-843, was determined. The genomeof M. aeruginosa is a single, circular chromosome of 5 842 795base pairs (bp) in length, with an average GC content of 42.3%.The chromosome comprises 6312 putative protein-encoding genes,two sets of rRNA genes, 42 tRNA genes representing 41 tRNA species,and genes for tmRNA, the B subunit of RNase P, SRP RNA, and6Sa RNA. Forty-five percent of the putative protein-encodingsequences showed sequence similarity to genes of known function,32% were similar to hypothetical genes, and the remaining 23%had no apparent similarity to reported genes. A total of 688kb of the genome, equivalent to 11.8% of the entire genome,were composed of both insertion sequences and miniature inverted-repeattransposable elements. This is indicative of a plasticity ofthe M. aeruginosa genome, through a mechanism that involveshomologous recombination mediated by repetitive DNA elements.In addition to known gene clusters related to the synthesisof microcystin and cyanopeptolin, novel gene clusters that maybe involved in the synthesis and modification of toxic smallpolypeptides were identified. Compared with other cyanobacteria,a relatively small number of genes for two component systemsand a large number of genes for restriction-modification systemswere notable characteristics of the M. aeruginosa genome.     

Chromosome Number and Morphology in Vacuolaria virescens (Chloromonadophyceae)

Vacuolaria virescens Cienk. has a chromosome number of 97±2.At metaphase these range in size between small dot-like chromosomes1 um in diameter to rod-shaped structures 12 µm long.Centromeres and less densely stained regions of chromosomesare recognizable.     

Comparative mapping of HKT genes in wheat, barley, and rice, key determinants of Na+ transport, and salt tolerance

Salt tolerance of plants depends on HKT transporters (High-affinityK⁺ Transporter), which mediate Na⁺-specific transport or Na⁺-K⁺co-transport. Gene sequences closely related to rice HKT geneswere isolated from hexaploid bread wheat (Triticum aestivum)or barley (Hordeum vulgare) for genomic DNA southern hybridizationanalysis. HKT gene sequences were mapped on chromosomal armsof wheat and barley using wheat chromosome substitution linesand barley–wheat chromosome addition lines. In addition,HKT gene members in the wild diploid wheat ancestors, T. monococcum(A^m genome), T. urartu (A^u genome), and Ae. tauschii (D^t genome)were investigated. Variation in copy number for individual HKTgene members was observed between the barley, wheat, and ricegenomes, and between the different wheat genomes. HKT2;1/2-like,HKT2;3/4-like, HKT1;1/2-like, HKT1;3-like, HKT1;4-like, andHKT1;5-like genes were mapped to the wheat–barley chromosomegroups 7, 7, 2, 6, 2, and 4, respectively. Chromosomal regionscontaining HKT genes were syntenic between wheat and rice exceptfor the chromosome regions containing the HKT1;5-like gene.Potential roles of HKT genes in Na⁺ transport in rice, wheat,and barley are discussed. Determination of the chromosome locationsof HKT genes provides a framework for future physiological andgenetic studies investigating the relationships between HKTgenes and salt tolerance in wheat and barley. Key words: Barley, comparative mapping, HKT, rice, salt tolerance, sodium transport, wheat