Analysis of nuclear and organellar DNA of somatic hybrid calli and plants between Lycopersicon spp. and Nicotiana spp.

Protoplast fusion experiments between Lycopersicon esculentum or L. peruvianum and Nicotiana tabacum or N. plumbaginifolia were performed to investigate the possibility of producing symmetric and asymmetric somatic hybrids between these genera. These fusions, which involved 1.7 × 10⁸ protoplasts, yielded 35 viable hybrid calli. Plant regeneration was successful with two calli. One of these regenerants flowered, but developed no fruits. Analysis of the nuclear DNA by means of dot blot hybridization with species-specific repetitive DNA probes combined with flow cytometry, revealed that the nuclei of most hybrid calli contained the same absolute amount of Nicotiana DNA as the Nicotiana parent or (much) less, whereas the amount of Lycopersicon DNA per nucleus was 2–5 times that of the parental genotype. Eighteen of the 34 hybrids analyzed possessed Lycopersicon chloroplast DNA (cpDNA), whereas the other 16 had DNA from Nicotiana chloroplasts. The cpDNA type was correlated with the nuclear DNA composition; hybrids with more than 2C Nicotiana nuclear DNA possessed Nicotiana chloroplasts, whereas hybrids with 2C or less Nicotiana nuclear DNA contained Lycopersicon chloroplasts. Mitochondrial DNA (mtDNA) composition was correlated with both nuclear DNA constitution and chloroplast type. Hybrids possessed only or mainly species-specific mtDNA fragments from the parent predominating in the nucleus and often providing the chloroplasts. The data are discussed in relation to somatic incompatibility which could explain the low frequency at which hybrids between Lycopersicon and Nicotiana species are obtained and the limited morphogenetic potential of such hybrids.     

Plant regeneration from protoplasts of a commercial Asian long-grain javanica rice

A reproducible plant regeneration system has been developed for protoplasts from embryogenic cell suspension cultures of the commercial Asian long-grain javanica rice, Oryza sativa cv. Azucena. Protoplasts were isolated routinely from cell suspensions with yields of 5.5–12.0 × 10⁶ g^-1 fresh weight. A membrane filter nurse-culture method was adopted and was essential to support sustained mitotic division of protoplast-derived cells, leading to cell colony formation. The protoplast plating efficiency was higher when suspension cells of Lolium multiflorum, rather than those of the japonica rice O. sativa L. cv. Taipei 309, were employed as nurse cells. A two-step shoot regeneration procedure, in which protoplast-derived calli were cultured initially on medium semi-solidified with 1% (w/v) agarose followed by culture on medium containing 0.4% (w/v) agarose, induced plant regeneration from protoplast-derived calli. Fifteen percent of protoplast-derived tissues regenerated shoots; tissues not subjected to this treatment failed to develop shoots.     

Nuclear behaviour of colonies and regenerated buds from protoplasts ofNicotiana plumbaginifolia Viviani haploids

The ploidy level variations of protoplast cultures ofNicotiana plumbaginifolla Viviani (n=10) were investigated from protoplast isolation until regenerated buds, using cytophotometric measurements of nuclear DNA content and chromosome counting. An increase in the average nuclear DNA amount has been found to occur in freshly isolated protoplasts after 15 hours of maceration. Cytological abnormalities like nuclear fragmentation, chromatin connections between interphasic nuclei and micronuclei were observed during the following days. Chromosome counting in 15, 30 and 50-day-old calli and in regenerated buds revealed that nuclei are haploid, diploid or aneuploid.Abbreviations p-cells, p-calli or p-colonies protoplast-derived cells, calli or colonies - BAP 6-benzylaminopurine - NAA 1-naphtaleneacetic acid - 2iP ²-isopentyl-aednine     

Plant regeneration from protoplasts of the monocotyledonous Haworthia magnifica v. Poelln.

Calli were initiated from flower buds, gynoecia and inflorescence segments of Haworthia magnifica v. Poelln. and subcultured on solid medium. Two liquid culture steps were necessary to prepare the calli for the isolation of protoplasts capable of sustained cell divisions. Plants were regenerated from protoplast-derived calli. The influence of both the osmolality of the culture media and exudates on the viability of protoplasts and protoplast-derived cell colonies is briefly discussed.     

Somatic hybrids produced by protoplast fusion between S. tuberosum and S. brevidens: phenotypic variation under field conditions

Summary Phenotypic and flowering characteristics of hybrid plants generated by protoplast fusion between a tetraploid S. tuberosum line and diploid S. brevidens were assessed under field conditions. Hybrids were compared to both clonal parental material and protoplast-derived plants of each parent. Almost all of the hybrids were hexaploid. A wide range of variation in morphological characters was observed for hybrids and protoclones. Flowering was markedly reduced in protoclones. The majority of hybrids flowered, had viable pollen and set tubers. Tuber and pollen characteristics of hybrids produced from individual fusion calli also varied. The potential usefulness of fusion hybrids in potato improvement is discussed.     

Asymmetric protoplast fusion aimed at intraspecific transfer of cytoplasmic male sterility (CMS) in Lolium perenne L.

Summary Techniques have been developed for the production of cybrids in Lolium perenne (perennial ryegrass). Gamma-irradiated protoplasts of a cytoplasmically male-sterile breeding line of perennial ryegrass (B200) were fused with iodoacetamide-treated protoplasts of a fertile breeding line (Jon 401). After fusion 25 putative cybrid calli were characterized to determine mitochondrion type and composition of the nuclear genome. Analysis of phosphoglucoisomerase isozyme profiles and determination of the ploidy level by flow cytometry indicated that all of the calli tested essentially contained the nuclear DNA of the fertile line. However, the presence of parts of the nuclear DNA from the sterile line could not be excluded. Southern blotting of total DNA isolated from the parental lines and putative cybrids combined with hybridizations using the mitochondrial probes cox1 and atp6 revealed that the mitochondria of the calli originated from the fertile line (5 calli), the sterile line (5 calli) or from both parental lines (15 calli). The hybridization patterns of the mtDNA from the cybrid calli showed extensive quantitative and qualitative variation, suggesting that fusion-induced inter- or intramolecular mitochondrial recombination had taken place.     

Detection of protoplast-derived DNA tetraploid Lisianthus (Eustoma grandiflorum) plants by leaf and flower characteristics and by flow cytometry

Plants of lisianthus (Eustoma grandiflorum (Griesbach)Schinners=Lisianthus russellianus Hook.) were regenerated from protoplasts and grown in pots until flowering. Vegetative and floral characteristics were measured and compared with parent plants. Larger leaves and petals and longer guard cells, sepals and filaments were recorded from protoplast-derived plants suggestive of polyploidy. The nuclear DNA contents of protoplast-derived and parental plants were determined by flow cytometry. Protoplast-derived plants were confirmed as DNA tetraploid by flow cytometry with a DNA index of 1.95. Their nuclear DNA content was measured as 6.33±0.04 pg DNA per 2C nucleus compared with 3.26±0.10 pg DNA per 2C nucleus from parental plants. Polyploidisation induced during protoplast regeneration offers an alternative to that of colchicine treatment.     

Somatic embryogenesis and fertile green plant regeneration from suspension cell-derived protoplasts of rye (<Emphasis Type="Italic">Secale cereale</Emphasis> L.)

A method for somatic embryogenesis and fertile green plant regeneration from suspension cell-derived protoplasts of rye (Secale cereale L. cv. Auvinen) was developed. Fast-growing and friable embryogenic calli with a high regeneration capacity were induced from immature rye inflorescences using modified MS medium. These friable embryogenic calli were used for suspension culture initiation in liquid AA medium. A high yield of protoplasts was obtained from suspension cell clumps after 3–5 days of subculture. Isolated protoplasts were cultured in KM8p medium. The frequency of protoplast cell divisions and colony formations in liquid culture medium were similar to those on agarose-solidified medium. Compact embryogenic calli were developed from protoplast-derived microcalli in growth medium mMS. Approximately 7% of the transferred embryogenic calli produced green shoots on N₆ regeneration medium. Of 33 green plants, 28 were fertile with normal flowering and seed set. The ratio of green and albino plantlets was 1:4. Rye protoplast-derived green plants showed normal diploid characters as determined by flow cytometer analysis and chromosome counting.Abbreviations 2,4-D 2,4-Dichorophenoxyacetic acid - FDA Fluorescein diacetate - FW Fresh weight - GA₃ Gibberellic acid - Kinetin 6-Furfurylaminopurine - IAA Indole-3-acetic acid - NAA -Naphthaleneacetic acid     

Analysis of mitochondrial genomes amongCitrus plants produced by the interspecific somatic fusion of ‘Seminole’ tangelo with rough lemon

Interspecific somatic fusion was performed between Seminole tangelo (Citrus reticulata Blanco xC. paradisi Macf.) protoplasts isolated from embryogenic callus and rough lemon (C. jambhiri Lush.) mesophyll protoplasts. Eight plants out of ten randomly selected regenerants had 18 chromosomes and the same nuclear rDNA fragment patterns as that of the mesophyll parent. The remaining two plants showed rDNA fragment patterns from both parents and had 36 chromosomes. For the analysis of mitochondrial DNA (mtDNA),rrn26 derived from pea was used to probeBamHI digests of the regenerants. All plants showed mtDNA band patterns identical to that of the callus parent, suggesting that eight plants were cybrids and the remaining two plants were somatic hybrids. In addition to the callus parent band patterns, additional fragments from the mesophyll parent and/or a novel band fragment were revealed in some of the putative cybrids by peaatpA probe after digestion withDraI andPstI. These results suggest the occurrence of mtDNA recombination/rearrangement inCitrus cybrids produced by somatic fusion in this interspecific combination.Abbreviations mtDNA Mitochondrial DNA     

Rapid chloroplast segregation and recombination of mitochondrial DNA in Brassica cybrids

Summary Brassica cybrids were obtained after fusing protoplasts of fertile and cytoplasmic male sterile (CMS) B. napus lines carrying the original b. napus, and the Ogura Raphanus sativus cytoplasms, respectively. Iodoacetate treatment of the fertile line and X-irradiation of the CMS line prevented colony formation from the parental protoplasts. Colony formation, however, was obtained after protoplast fusion. Hybrid cytoplasm formation was studied in 0.5 g to 5.0 g calli grown from a fused protoplast after an estimated 19 to 22 cell divisions. Chloroplasts and mitochondria were identified in the calli by hybridizing appropriate DNA probes to total cellular DNA. Out of the 42 clones studied 37 were confirmed as cybrids. Chloroplast segregation was complete at the time of the study. Chloroplasts in all of the cybrid clones were found to derive from the fertile parent. Mitochondrial DNA (mtDNA) segregation was complete in some but not all of the clones. In the cybrids, mtDNA was different from the parental plants. Physical mapping revealed recombination in a region which is not normally involved in the formation of subgenomic mtDNA circles. The role of treatments used to facilitate the recovery of cybrids, and of organelle compatibility in hybrid cytoplasm formation is discussed.     

Plant regeneration from the protoplasts of Solanum tuberosum, S. nigrum and S. bulbocastanum

The mesophyll protoplasts were isolated from the Solanum tuberosum (S. tbr) clones of different ploidy level (4x Bzura cv., 2x H-8105, and 2x ZEL-1136) as well as from the wild species: S. bulbocastanum (S. blb, 2x) and two accessions of S. nigrum (S. ngr, 6x). Additionally, the protoplasts were isolated from the cell suspensions of Bzura cv. and H-8105 clone. The conditions of protoplast isolation as well as the media for their culturing and regeneration, were selected and optimized for the studied genotypes. For mesophyll protoplasts, the shooting calli were produced by all the cultured protoclones except that of S. bulbocastanum. The shoots excised from the protoplast-derived calli developed into whole plants in all the studied potato clones but only in one accession of S. nigrum, i.e. S. ngr var. gigantea. As for suspension-cell-derived protoplasts, only H-8105 clone produced the regenerative type of calli, though normal shoots could not be obtained. The regenerative capacity of the protoplasts isolated from leaves and cell suspensions is compared and discussed. We regret to report the death of M. Sc. Maria Borkowska after the completion of this work.     

Chemical and genetic characterization of calli derived from somatic hybridization between tansy (Tanacetum vulgare L.) and pyrethrum (Tanacetum cinerariifolium (Trevir.) Schultz-Bip.)

 Pyrethrum (Tanacetum cinerariifolium (Trevir.) Schultz-Bip.) produces environmentally benign pesticides, the pyrethrins, and tansy (Tanacetum vulgare L.) lower terpenes of variable biological effectiveness. As an approach to improve the oil content and composition of tansy for enhanced biological activity, a somatic hybridization technique between tansy and pyrethrum was established. About 1×10⁶ of leaf-mesophyll protoplasts of both species were mixed and fused with a solution containing 15% polyethylene glycol. Light-green and yellowish calli developed from the fusion experiments. The fusion-derived calli grew vigorously on MS medium supplemented with 6.4 mg l^-1 of BAP, 0.8 mg l^-1 of NAA, and 30–40 g l^-1 of glucose. Nuclear DNA content, RAPD patterns, and volatile compounds were analyzed to determine the hybridity of the calli. The nuclear DNA content of the tansy and pyrethrum genotypes, and the protoplast-derived calli of tansy were 6.41, 7.39, 13.84, and 8.11 pg, respectively. The nuclear DNA content of individual calli derived from the protoplast fusion between tansy +tansy ranged from 8.84 (F43A) to 19.59 pg (F43C) while those of the tansy+pyrethrum fusions were 10.66 (F46A) and 31.87 pg (F46B). Using four 10-mer primers a total of 56 RAPD-PCR fragments were produced. The distance matrices of fragments were calculated by average linkage cluster analysis. Two visually separated clusters were observed. One cluster consisted of the two tansy genotypes and the fusion-derived callus F43A; the other consisted of pyrethrum and fusion-derived calli F46B and F46C. Volatile compounds, such as decadienal, artedouglasia oxide, heptadecane, syringaldehyde and coniferyl alcohol, analyzed by gas chromatography mass spectrometry, were found only in the protoplast fusion-derived calli F43A and F46B. Several less volatile compounds were also detected only in fusion calli. Hexadecanoic and linoleic acids were common to fusion-derived calli and tansy, and one unknown compound to fusion-derived calli and pyrethrum. Pyrethrins I and II were detected from pyrethrum, but not from the fusion-derived calli. The additive nuclear DNA content of protoplast fusion-derived calli and the results of the RAPDs suggest that interspecific fusions had occurred. The small number of volatile compounds detected from both the fusion calli and from the donor species indicates that the unorganized callus tissue is unable to produce tissue-specific volatile compounds. Received: 4 August 1998 / Accepted: 30 September 1998     

线粒体DNA U4b单倍群:中国塔吉克族高原原发性高血压的遗传易感因素

目的:探讨线粒体DNA变异与中国塔吉克族高原原发性高血压的关系.方法:在中国塔吉克族人群中,收集了 53例高原原发性高血压病例和46例正常对照.通过PCR扩增线粒体DNA片段,经测序拼接获得线粒体全基因组,与剑桥序列比对以筛选线粒体DNA变异,分析在病例组与对照组中的分布差异,采用生物信息学工具预测阳性相关变异的功能....     

The mutagenic effect of gamma rays on leaf protoplasts of haploid and dihaploid Nicotiana plumbaginifolia,estimated by valine resistance mutation frequencies

Summary Leaf protoplasts isolated from haploid and dihaploid Nicotiana plumbaginifolia plantlets were treated with different doses of gamma-rays and their survival was determined by scoring for plating efficiency at each irradiation dose. A fixed number of surviving protoplast-derived colonies was then plated in the presence of inhibitory concentrations of L-valine and incubated until growing resistant calli could be scored and mutation rates calculated. Though haploid protoplasts were found to be a little more sensitive than dihaploids to the lethal effect of radiation, the two dose-response curves of gamma-rays that induced mutagenesis were very similar. The irradiation dose capable of causing a ten-fold increase of spontaneous mutation frequencies was about 500 rads with both haploid and dihaploid protoplasts.Contribution No. 2173 of the Biology Radiation Protection and Medical Research Programme, Directorate General XII of the Commission of the European Communities     

Analysis of nuclear and organellar DNA of somatic hybrid calli and plants between Lycopersicon spp. and Nicotiana spp.

Protoplast fusion experiments between Lycopersicon esculentum or L. peruvianum and Nicotiana tabacum or N. plumbaginifolia were performed to investigate the possibility of producing symmetric and asymmetric somatic hybrids between these genera. These fusions, which involved 1.7 × 10⁸ protoplasts, yielded 35 viable hybrid calli. Plant regeneration was successful with two calli. One of these regenerants flowered, but developed no fruits. Analysis of the nuclear DNA by means of dot blot hybridization with species-specific repetitive DNA probes combined with flow cytometry, revealed that the nuclei of most hybrid calli contained the same absolute amount of Nicotiana DNA as the Nicotiana parent or (much) less, whereas the amount of Lycopersicon DNA per nucleus was 2–5 times that of the parental genotype. Eighteen of the 34 hybrids analyzed possessed Lycopersicon chloroplast DNA (cpDNA), whereas the other 16 had DNA from Nicotiana chloroplasts. The cpDNA type was correlated with the nuclear DNA composition; hybrids with more than 2C Nicotiana nuclear DNA possessed Nicotiana chloroplasts, whereas hybrids with 2C or less Nicotiana nuclear DNA contained Lycopersicon chloroplasts. Mitochondrial DNA (mtDNA) composition was correlated with both nuclear DNA constitution and chloroplast type. Hybrids possessed only or mainly species-specific mtDNA fragments from the parent predominating in the nucleus and often providing the chloroplasts. The data are discussed in relation to somatic incompatibility which could explain the low frequency at which hybrids between Lycopersicon and Nicotiana species are obtained and the limited morphogenetic potential of such hybrids.     

The organization of genes in yeast mitochondrial DNA

Summary We have fractionated fragments of yeast mtDNA, obtained with restriction endonucleases, on poly(U)-Sephadex columns using the procedure of Flavell and Van den Berg (FEBS Letters (1975) 58, 90–93). The poly(U) forms a triple helix with (dA·dT) clusters in duplex DNA and fractionates DNA fragments on the basis of the length and number of clusters contained in them.mtDNA fragments obtained with endonucleases PstI, BamHI, HindII, HindII+III, EcoRI, HapII and HhaI were separated by poly(U)-Sephadex in three groups: fragments not retained by the column in 2M LiCl, fragments partially retained and fragments (nearly) completely bound in 2 M LiCl and only eluted by 0.1 M LiCl. The separation obtained is adequate for analytical fractionation of fragments and it can be used for the preparative isolation of firmly-bound fragments.In mtDNA digests made with endonuclease HapII, which gives about 70 separable fragments under our conditions, only about 10% of the fragments were firmly bound to poly(U)-Sephadex. This shows that the number of (dA·dT) clusters long enough to result in binding is limited in yeast mtDNA and its suggests that large fragments are bound by only one or a few clusters.Corresponding segments of the physical map of the mtDNAs from Saccharomyces carlsbergensis and Saccharomyces cerevisiae strains JS1-3D and KL14-4A were bound to the column, showing that the (dA·dT) clusters responsible for binding are conserved in the evolution of mtDNA. However, one 3,000 bp insert, only present on KL14-4A mtDNA, causes the loss of a binding site, another long insert introduces a new binding site.Fragments firmly bound to the columns are clustered in one quadrant of the physical map of these three mtDNAs. This quadrant also contains the large insertions present in KL14-4A mtDNA and absent from S. carlsbergensis mtDNA. The possible relation between (dA·dT) clusters and insertions is discussed.Abbreviation bp base pairs     

Relative Rates of Nucleotide Substitution in Frogs

Accurate estimation of relative mutation rates of mitochondrial DNA (mtDNA) and single-copy nuclear DNA (scnDNA) within lineages contributes to a general understanding of molecular evolutionary processes and facilitates making demographic inferences from population genetic data. The rate of divergence at synonymous sites (K_s) may be used as a surrogate for mutation rate. Such data are available for few organisms and no amphibians. Relative to mammals and birds, amphibian mtDNA is thought to evolve slowly, and the K_s ratio of mtDNA to scnDNA would be expected to be low as well. Relative K_s was estimated from a mitochondrial gene, ND2, and a nuclear gene, c-myc, using both approximate and likelihood methods. Three lineages of congeneric frogs were studied and this ratio was found to be approximately 16, the highest of previously reported ratios. No evidence of a low K_s in the nuclear gene was found: c-myc codon usage was not biased, the K_s was double the intron divergence rate, and the absolute K_s was similar to estimates obtained here for other genes from other frog species. A high K_s in mitochondrial vs. nuclear genes was unexpected in light of previous reports of a slow rate of mtDNA evolution in amphibians. These results highlight the need for further investigation of the effects of life history on mutation rates. Current address (Andrew J. Crawford): Smithsonian Tropical Research Institute, Apartado 2072, Balboa, Ancon, Republic of Panama     

Somatic hybridization between Lycopersicon esculentum and Lycopersicon pennellii

Summary Selection and screening methods were devised which resulted in the identification of a number of somatic hybrid callus clones following fusion of Lycopersicon esculentum protoplasts and L. pennellii suspension culture protoplasts. Visual selection for callus morphology combined with a high fusion frequency and irradiation of one parental protoplast type (¹³⁷Cs source, 1.5 Krads) resulted in selection of a callus clone population containing a high proportion of somatic hybrids. Analysis of a dimeric isozyme for the presence of a heterodimeric form was found to be satisfactory for distinguishing parental-type calli, somatic hybrid calli, and mixed calli derived from both types of unfused parental cells. No somatic hybrid calli produced shoots, although the sexual hybrid between L. esculentum and L. pennellii regenerated well under the culture conditions employed. This result suggests that the non-regenerable growth habit of the L. pennellii suspension culture was dominant in the somatic hybrid. The culture conditions described here are suitable for obtaining regenerated plants from L. esculentum mesophyll protoplasts. L. esculentum protoplast calli from fusion cultures gave rise to shoots with L. esculentum phenotype at higher frequency than calli from control unfused L. esculentum mesophyll protoplast cultures. The use of probes for species-specific organelle DNA fragments allowed identification of organelle DNA restriction fragments in digests of total DNA from small samples of individual callus clones. The callus clones analyzed either carried predominantly one parental plastid DNA type or mixtures of both types. Use of a mitochondrial DNA (mtDNA) probe which distinguishes two parental mtDNA fragments revealed that the L. pennellii-specific fragment was present in all clones examined, but the L. esculentum fragment was absent or in low proportion.     

Variation of the Mitochondral Genome in the Evolution of Drosophila

The evidence on mitochondrial genome variation and its role in evolution of the genus Drosophila are reviewed. The mitochondrial genome is represented by a circular double-stranded DNA molecule 16 to 19 kb in length. Mitochondrial genes lack introns and recombination. The entire mitochondrial genome can be arbitrarily divided into three parts: (1) protein-coding genes; (2) genes encoding rRNA and tRNA; and (3) the noncoding regulatory region (A + T region). The selective importance of mutations within different mtDNA regions is therefore unequal. In Drosophila, the content of the A + T pairs in mtDNA is extremely high and a pattern of nucleotide substitution is characterized by a low transition/transversion ratio (and a low threshold of mutation saturation). The deletions and duplications are of common occurrence in the mitochondrial genome. However, this genome lacks such characteristic for the nuclear genome aberrations as inversions and transpositions. The phenomena of introgression and heteroplasmy provide an opportunity to study the adaptive role of the mitochondrial genome and its role in speciation. Analysis of evidence concerning mtDNA variation in different species of the genus Drosophilamade it possible to ascertain data on phylogenetic relationships among species obtained by studying nuclear genome variation. In some species, mtDNA variation may serve as a reliable marker for population differentiation within a species, although evidence on the population dynamics of the mtDNA variation is very scarce.