Restoration of fertility in cytoplasmic male sterile (CMS) Nicotiana Sylvestris by fusion with X-irradiated N. tabacum protoplasts

Comparative transcriptome analysis in Chinese cabbage (Brassica rapa ssp. pekinesis) for DEGs of Ogura-, Polima-CMS and their shared maintainer

Cytoplasmic male sterility (CMS) is maternally inherited trait, which hinders the ability to produce viable pollen in plants. It serves as a useful tool for hybrid seed production via exploiting heterosis in crops. The molecular mechanism of CMS and fertility restoration has been investigated in different crops. However, limited number of reports is available on comparison of Ogura- and Polima-CMS with their shared maintainer in Chinese cabbage. We performed transcript profiling of sterile Ogura CMS (Tyms), Polima CMS (22m2) and their shared maintainer line (231-330) with an aim to identify genes associated with male sterility. In this work, we identified 912, 7199 and 6381 DEGs (Differentially Expressed Genes) in 22m2 Vs Tyms, 231-330 VS 22m2 and 231-330 Vs Tyms, respectively. The GO (Gene Ontology) annotation and KEGG pathway analysis suggested that most of the DEGs were involved in pollen development, carbon metabolism, lipase activity, lipid binding, penta-tricopeptide repeat (PPR), citrate cycle and oxidative phosphorylation, which were down-regulated in both CMS lines. This result will provide an important resource for further understanding of functional pollen development, the CMS mechanism and to improve molecular breeding in Chinese cabbage.

Ogura-CMS in Chinese cabbage (Brassica rapa ssp. pekinensis) causes delayed expression of many nuclear genes

We investigated the mechanism regulating cytoplasmic male sterility (CMS) in Brassica rapa ssp. pekinensis using floral bud transcriptome analyses of Ogura-CMS Chinese cabbage and its maintainer line in B. rapa 300-K oligomeric probe (Br300K) microarrays. Ogura-CMS Chinese cabbage produced few and infertile pollen grains on indehiscent anthers. Compared to the maintainer line, CMS plants had shorter filaments and plant growth, and delayed flowering and pollen development. In microarray analysis, 4646 genes showed different expression, depending on floral bud size, between Ogura-CMS and its maintainer line. We found 108 and 62 genes specifically expressed in Ogura-CMS and its maintainer line, respectively. Ogura-CMS line-specific genes included stress-related, redox-related, and B. rapa novel genes. In the maintainer line, genes related to pollen coat and germination were specifically expressed in floral buds longer than 3mm, suggesting insufficient expression of these genes in Ogura-CMS is directly related to dysfunctional pollen. In addition, many nuclear genes associated with auxin response, ATP synthesis, pollen development and stress response had delayed expression in Ogura-CMS plants compared to the maintainer line, which is consistent with the delay in growth and development of Ogura-CMS plants. Delayed expression may reduce pollen grain production and/or cause sterility, implying that mitochondrial, retrograde signaling delays nuclear gene expression.

Genetic transfer in plants through interspecific protoplast fusion

Protoplasts of sexually incompatible species have been fused and in some combinations have given rise to somatic hybrid plants. Partial elimination of parental chromosomes from either species is common in such hybrids, but total chromosome loss has generally occurred only with phylogenetically unrelated pairings. Genetic function of one parent may be retained despite a complete loss of its chromosomes, suggesting that genetic introgression is possible in the absence of complete donor chromosomes. A model interspecific combination for such studies is the potato-tomato somatic hybrid for which numerous phenotypes and karyotypes are encountered at the outset, with a broader range observed in the second somatic generation.

Defective cell proliferation in the floral meristem of alloplasmic plants of Nicotiana tabacum leads to abnormal floral organ development and male sterility

Flowers of an alloplasmic male-sterile tobacco line, comprised of the nuclear genome of Nicotiana tabacum and the cytoplasm of Nicotiana repanda, develop short, poorly-pigmented petals and abnormal sterile stamens that often are fused with the carpel wall. The development of flower organ primordia and establishment of boundaries between the different zones in the floral meristem were investigated by performing expression analysis of the tobacco orthologs of the organ identity genes GLO, AG and DEF. These studies support the conclusion that boundary formation was impaired between the organs produced in whorls 3 and 4 resulting in partial fusions between anthers and carpels. According to the investigations cell divisions and floral meristem size in the alloplasmic line were drastically reduced in comparison with the male-fertile tobacco line. The reduction in cell divisions leads to a discrepancy between cell number and cell determination at the stage when petal and stamen primordia should be initiated. At the same stage expression of the homeotic genes was delayed in comparison with the male-fertile line. However, the abnormal organ development was not due to a failure in the spatial expression of the organ identity genes. Instead the aberrant development in the floral organs of whorls 2, 3 and 4 appears to be caused by deficient floral meristem development at an earlier stage. Furthermore, defects in cell proliferation in the floral meristem of the alloplasmic male-sterile line correlates with presence of morphologically modified mitochondria. The putative causes of reduced cell number in the floral meristem and the consequences for floral development are discussed.

Effect of(12)C (+5) ion beam irradiation on cell viability and plant regeneration in callus, protoplasts and cell suspensions ofLavateva thuringiaca

The biological effects of irradiation with(12)C(+5) ion beam on plant cells have been analyzed. Protoplasts and cell suspensions ofLavatera thuringiaca, and a somatic hybrid callus (Hibiscus rosa-sinensis +Lavatera thuringiaca), were irradiated with doses from 0.05 to 50 Gy, and the effects on cell growth, cell division, cell viability and embryogenesis rates were analyzed. Irradiation with(12)C(+5) ion beam at relatively very low doses (5.0 Gy) significantly inhibited cell division, yet the survival rate and regeneration capability of the cells through somatic embryogenesis were conserved in more than 70 and 50 %, respectively. These results indicate that cell division is the most sensitive parameter to irradiation, accounting for the inhibition of colony formation and callus growth. The potential use of the(12)C(+5) ion beam in asymmetric protoplast fusion experiments is discussed.

Cybrid production based on mutagenic innactivation of protoplasts and rescuing of mutant plastids in fusion products: Potato with a plastome fromS. bulbocastanum andS. pinnatisectum

A procedure for cybrid production, based on double treatment of donor protoplasts by physical and afterwards chemical mutagens at superlethal doses (γ-irradiation at a dose of 1000 Gy was applied for the inactivation of nuclei; 3-5 mMN-nitroso-N-methylurea was used for the efficient induction of plastome mutation) and the rescuing of mutant plastids after fusion with untreated recipient protoplasts, was developed. For identification of mutant donor-type plastids in fusion products a selection for streptomycin was performed. In two sets of experiments, in whichS. tuberosum served as the recipient of foreign cytoplasm with the wild tuber-bearing speciesS. bulbocastanum andS. pinnatisectum as donors, a total of about 40 streptomycin-resistant colonies was isolated. Eight regenerants from theS. tuberosum+S. bulbacastanum fusion combination and four fromS. tuberosum+S. pinnatisectum were further investigated using chromosome counting, analysis of esterase isoenzymes, restriction analysis of organelle DNA, and blot hybridization. All but one plant from both combinations were characterised as potato cybrids possessing exclusively foreign plastids and retaining a morphology typical of the recipient. Only in one line was rearranged mtDNA detected. The availability of potato cybrids facilitates the analysis of plastome-encoded breeding traits and the identification of the most valuable source of cytoplasm among the wild potato species. The described system for producing cybrids without genetic selectable markers in the parental material offers the possibility for the rescue of cytoplasmic mutations which are impossible to isolate by conventional approaches.

Analysis of the mitochondrial DNA of the somatic hybrids of Solanum brevidens and S. tuberosum using non-radioactive digoxigenin-labelled DNA probes

Mitochondrial (mt) DNAs of somatic hybrids obtained by electrical and chemical fusion of mesophyll protoplasts of S. brevidens and a dihaploid line of S. tuberosum PDH 40 were analysed by Southern hybridization using the digoxigenin-labelled mtDNA sequences nad5 or orf25. In the Southern analysis of the hybrid mtDNA probed with nad5, most of the 19 hybrids analyzed had an RFLP pattern similar, but not identical, to one of the parents, S. tuberosum, PDH40. Nineteen percent of the hybrids had most of the S. brevidens fragments. Five of the hybrids had an identical RFLP pattern to either one of the parents while another two hybrids had novel RFLP patterns. Similar results were obtained by Southern analysis with orf25. These results clearly show that mtDNA rearrangements had occurred at a high frequency in the somatic hybrids. There were no differences in the frequencies of rearrangements observed between the hybrids regenerated from chemical and electrical fusions.

Organelle analysis of symmetric and asymmetric hybrids between Lycopersicon peruvianum and Lycopersicon esculentum

The organelles of somatic hybrids obtained from symmetric and asymmetric fusions between the Lycopersicon species L. peruvianum and L. esculentum were analyzed by DNA hybridization methods. In the asymmetric fusions the L. peruvianum protoplasts were gamma-irradiated at a dose of 50, 300 and 1,000 Gy. The organelles were characterized using the Petunia chloroplast probe pPCY64 and the mitochondrial EcoRI-SalI fragment of the Pcf gene. In all symmetric and asymmetric hybrid plants, a total of 73 being analyzed, only one of the parental chloroplast genomes was present, except for one hybrid plant which harbored both parental chloroplast genomes. No recombination and/or rearrangement in the chloroplast genome could be identified with the pPCY64 probe. Irradiation of the L. peruvianum protoplasts did not significantly reduce the fraction of asymmetric hybrids with L. peruvianum chloroplasts. A novel mitochondrial restriction pattern was present in 5 out of 24 hybrids tested. In 9 hybrids novel combinations of chloroplasts and mitochondria were found, indicating that both organelle types sorted out independently.

Somatic hybridization by microfusion of defined protoplast pairs in Nicotiana: morphological, genetic, and molecular characterization

Somatic hybrid/cybrid plants were obtained by microfusion of defined protoplast pairs from malefertile, streptomycin-resistant Nicotiana tabacum and cytoplasmic male-sterile (cms), streptomycin-sensitive N. tabacum cms (N. bigelovii) after microculture of recovered fusants. Genetic and molecular characterization of the organelle composition of 30 somatic hybrid/cybrid plants was performed. The fate of chloroplasts was assessed by an in vivo assay for streptomycin resistance/ sensitivity using leaf explants (R0 generation and R1 seedlings). For the analysis of the mitochondrial (mt) DNA, species-specific patterns were generated by Southern hybridization of restriction endonuclease digests of total DNA and mtDNA, with three DNA probes of N. sylvestris mitochondrial origin. In addition, detailed histological and scanning electron microscopy studies on flower ontogeny were performed for representative somatic hybrids/cybrids showing interesting flower morphology. The present study demonstrates that electrofusion of individually selected pairs of protoplasts (microfusion) can be used for the controlled somatic hybridization of higher plants.

Modifications of floral development in tobacco induced by fusion of protoplasts of different male-sterile cultivars

Protoplasts derived from different cytoplasmic male-sterile cultivars of Nicotiana tabacum were fused. Nearly 200 cybrid calli were regenerated into plants and their flower morphologies were examined. Most cybrids exhibited parental-type male-sterile morphologies. Some, however, showed novel male-sterile phenotypes or phenotypes which combined traits of both male-sterile parents in a new combination. Others were restored to fertility, with stamens which produced functional pollen.

Plant regeneration from cytoplasmic hybrids of rice (Oryza sativa L.)

We obtained cybrid plants by electrofusing γ-irradiated protoplasts of a cytoplasmic male-sterile line "A-58 CMS" (Oryza sativa L.) and iodoacetamide (IOA)-treated protoplasts of the fertile (normal) rice cultivar "Fujiminori". The cybridity of the plants was confirmed by mitochondrial (mt) DNA restriction endonuclease, and plasmid-like DNA analyses, and by isozyme, cytological and morphological investigations. The chromosome number of the cybrid plants is 24.

Asymmetric hybridization between cytoplasmic male-sterile (CMS) and fertile rice (Oryza safiva L.) protoplasts

(60)Co-irradiated protoplasts of the cytoplasmic male-sterile line A-58 CMS (Oryza saliva L.) were electrofused with iodoacetamide (IOA)-treated protoplasts of the fertile (normal) rice cultivar 'Fujiminori'. Seven of the colonies that formed were identified as cytoplasmic hybrids (cybrids): they all had the peroxidase isozymes of the fertile 'Fujiminori' parent, but contained four plasmid-like DNAs (Bl, B2, B3 and B4) from the sterile A-58 CMS parent in their mitochondrial genomes. In addition, digestion of cybrid mtDNA gave a set of restriction fragments that differed from those of the parents.

Intergeneric asymmetric hybrids between Nicotiana plumbaginifolia and Atropa belladonna obtained by "gamma-fusion"

Asymmetric nuclear hybrids have been obtained by fusion of cells from a nitrate-reductase deficient mutant of Nicotiana plumbaginifolia (cnx20) and gamma irradiated protoplasts of Atropa belladonna (irradiation doses tested were 10, 30, 50 and 100 krad). The hybrid formation frequency following selection for genotypic complementation in the NR function was in the range of 0.7%-3.7%. Cytogenetic studies demonstrated that all hybrid plants tested possessed multiple (generally tetra- or hexaploid) sets of N. plumbaginifolia (n = 10) chromosomes along with 6-29 Atropa chromosomes (n = 36), some of which were greatly deleted. Besides the cnxA gene (the selection marker), additional material of the irradiated partner was expressed in some of the lines, as shown by analyses of multiple molecular forms of enzymes. Surprisingly, rDNA genes of both parental species were present and amplified in the majority of the hybrids. Whenever studied, the chloroplast DNA in the hybrids was derived from the Nicotiana parent. Regenerants from some lines flowered and were partially fertile. It is concluded that irradiation of cells of the donor parent before fusion can be used to produce highly asymmetric nuclear hybrid plants, although within the dose range tested, the treatment determined the direction of the elimination but not the degree of elimination of the irradiated genome.

Somatic hybridization in potato: use of γ-irradiated protoplasts of Solanum pinnatisectum in genetic reconstruction

Leaf mesophyll protoplasts of Solanum pinnatisectum (2n=24) γ-irradiated at doses of 200 Gy and consequently unable to divide were fused with untreated protoplasts of genomic chlorophyll deficient mutant IvP 841-1 (2n=24) containing the germplasms of S. tuberosum and S. phureja. Two types of plants differing in their pigmentation characteristics were selected. The regenerants of one group were identified as true somatic hybrids by using isozyme analyses of esterase and aspartate aminotransferase. The anthocyanin marker of S. pinnatisectum was phenotypically expressed in these regenerants and could be used as an additional selection trait for hybrid screening in this species combination. The regenerants of the second group were corrected for the gene controlling chlorophyll deficiency but contained species-specific isozymes of the potato cultivar only. Restriction analysis of chloroplast DNA revealed chloroplasts of the S. pinnatisectum type in all but one of the plants tested. The fusion experiments involving γ-irradiated protoplasts show that this approach in potato reconstruction has the advantage of producing a wide range of genetically novel plants.

Fusion-mediated combination of Ogura-type cytoplasmic male sterility with Brassica napus plastids using X-irradiated CMS protoplasts

X-irradiated protoplasts of a Brassica napus line carrying the Ogura Raphanus sativus male sterile cytoplasm were fused to protoplasts of male fertile B. napus cv. Olga. Plants were regenerated from six out of 34 randomly selected clones. In one clone, Bn(RS)26, a plant with male sterile flowers was obtained. Mitochondria of this plant are non-parental as revealed by DNA-DNA hybridization using a species specific probe. Its chloroplasts, however, derive from the fertile parent which results in loss of the sensitivity to low temperatures associated with R. sativus plastids in the male sterile parent. The novel cytoplasm of the Bn(RS)26 cybrid was transmitted through seed.

Identification of somatic hybrids in plant protoplast fusions with monoclonal antibodies to plasma-membrane antigens

Monoclonal antibodies generated by immunization with a plasma-membrane preparation from suspension-cultured cells of Nicotiana glutinosa L. were used in combination with fluoresceinor rhodamine-labeled goat anti-mouse immunoglobulins to identify heterokaryons in protoplast fusion procedures. Antibody labeling did not inhibit callus formation nor plantlet regeneration. The antibodies are non-invasive and surface labeling provides clear optical discrimination of true heterokaryons from unfused aggregates as well as from parental protoplasts and homokaryons. Labeling is stable throughout fusion and hence by pre-labeling parental protoplast populations the strategy is both versatile and of general applicability.

Restoration of male fertileNicotiana by fusion of protoplasts derived from two different cytoplasmic male-sterile cybrids

Using the 'donor-recipient' protoplast-fusion technique, we have recently constructed several alloplasmic-like lines ofNicotiana in which the original cytoplasms (or part of them) of eitherN. tabacum orN. sylvestris were replaced respectively, either byN. undulata or byN. bigelovii cytoplasms. These cybridizations resulted in two kinds of cytoplasmic male-sterile (CMS) cybrid plants:N. tabacum withN. undulata-like cytoplasm andN. sylvestris withN. bigelovii-like cytoplasm. Fusion of protoplasts, derived from the above two CMS types, by the 'donor-recipient' technique, lead to the recovery of 21 cybrid calli. One of these regenerated a cybrid with fertile pollen but having shortened filaments and slighly tappered anthers. Self pollination of the latter cybrid resulted in a second generation progeny having almost normal filaments and anthers. Further selfings produced a third generation in which numerous plants had normal stamens and fertile pollen. Mitochondrial DNA (mtDNA) analysis of second and third generation progenies revealed a novel pattern which differed from each of the parental CMS cybrids and also from the mtDNA of normal, male-fertileNicotiana species. The results suggest that mtDNA recombination between different types of CMS can lead to restoration of male-fertility.

A light sensitive recipient for the effective transfer of chloroplast and mitochondrial traits by protoplast fusion in Nicotiana

A light sensitive mutant was used as a recipient in the transfer of chloroplasts from a wildtype donor. Gamma irradiated (lethal dose) mesophyll protoplasts of Nicotiana gossei were fused with mesophyll protoplasts of a N. plumbaginifolia line carrying light sensitive plastids from a N. tabacum mutant. After fusion, colonies containing wild-type plastids from the cytoplasm donor were selected by their green colour. Most of the regenerated plants had N. plumbaginifolia morphology, but were a normal green in colour. The presence of donor-type plastids was confirmed by the restriction pattern of chloroplast DNA in each plant analysed. These cybrids were fully male sterile with an altered flower morphology typical of certain types of alloplasmic male sterility in Nicotiana. The use of the cytoplasmic light sensitive recipient proved to be suitable for effective interspecific transfer of wild-type chloroplasts. The recombinant-type mitochondrial DNA restriction patterns and the male sterility of the cybrids indicated the co-transfer of chloroplast and mitochondrial traits.

Transmission genetics of the somatic hybridization process in Nicotiana : 1. Hybrids and cybrids among the regenerates from cloned protoplast fusion products

Callus protoplasts of a Nicotiana tabacum chlorophyll-deficient mutant were fused with mesophyll protoplasts from one of following five sources: 4 cmsanalogs of tobacco bearing the cytoplasms of N. plumbaginifolia, N. suaveolens, N. repanda, and N. undulata, respectively, as well as wild species N. glauca. In another series of experiments, callus protoplasts from the chlorophyll-deficient genome Su/Su mutant of tobacco were fused with mesophyll protoplasts of the wild species N. glauca and those of a plastome chlorophyll-deficient tobacco mutant. The screening of hybrids consisted of visual identification followed by mechanical isolation and cloning of heteroplasmic fusion products in microdroplets of nutrient medium. Studies of regenerated plants included the analyses of gross morphology of plants, leaf and flower morphology, analysis of chromosome size and morphology and chromosome numbers, studies of multiple molecular forms of esterase and amylase, analysis of chloroplast DNA restriction patterns and analyses of chlorophyll-deficiency controlled by Su and P (-) genes. The study of progeny of 41 clones representing all species' combinations demonstrated that regenarants of most (63%) clones from intraspecific (for nuclear genes) combinations were cybrid forms, whereas in the case of the fusion N. tabacum + N. glauca, the true nuclear hybrids prevailed and the proportion of cybrids did not exceed 26%. Clones regenerating both hybrid and cybrid plants from the same fusion product were also found.

Intersectional cytoplasmic hybrids in Nicotiana : Identification of plastomes and chondriomes in N. sylvestris + N. rustica cybrids having N. sylvestris nuclear genomes

Cybrid plants having the nuclear genomes of one species and either or both plastomes and chondriomes of another species were obtained by fusing protoplasts of Nicotiana sylvestris, as "recipients", with X-irradiated protoplasts of N. rustica as "donors" of chloroplasts and mitochondria. Forty-nine flowering plants, derived from 28 calli, were analysed. As expected, they all had N. sylvestris (i.e. "recipients") morphology. Chloroplast DNA restriction patterns indicated that 8 and 41 plants had N. rustica and N. sylvestris plastomes, respectively. Some of the plants with either type of plastomes produced sterile pollen but none showed anther malformation typical to alloplasmic male sterility. Chondriome identification by mitochondrial DNA restriction analysis of cybrid plants revealed only restriction patterns which were either similar or identical to those of N. sylvestris while no cybrids with N. rustica restriction patterns were detected.

Cybrids containing mixed and sorted-out chloroplasts following interspecific somatic fusions in Nicotiana

Streptomycin resistance was transferred by "donor-recipient" protoplast fusion from Nicotiana tabacum (SR-1) protoplasts into Nicotiana tabacum (cytoplasmic male sterile - Line 92) protoplasts in one case and into Nicotiana sylvestris protoplasts in another. It is demonstrated that streptomycin resistance (SR-1) is a chloroplast marker which segregates independently from a mitochondrial marker.In the fusion experiment where Nicotiana tabacum (Line 92) was the recipient, microcalli were plated in the presence of streptomycin. In this case, chloroplast sorting out occurred at a stage preceeding plant regeneration, producing stable streptomycin resistant cybrids. In the fusion whre Nicotiana sylvestris was the recipient, no direct selection for streptomycin resistance was performed. In this case chloroplast sorting out was incomplete, thus producing cybrid plants with a mixed chloroplast population. In some plants, sorting out of streptomycin resistant and sensitive chloroplasts was still apparent in the second generation progeny.

Somatic hybridization in Nicotiana: behavior of organelles after fusion of protoplasts from male-fertile and male-sterile cultivars

Protoplasts from a nitrate reductase-deficient mutant of Nicotiana tabacum (cnx-68) were fused with protoplasts of 3 different cytoplasmically male-sterile cultivars of tobacco. Two cultivars had no stamens in the mature flowers and the third had petaloid structures in place of the stamens. Plants were regenerated from the fused protoplasts and characterized with respect to stamen development, chromosome number, and two chloroplast-coded traits. Nearly all hybrid plants displayed the chloroplast traits of only one parent, indicating that chloroplast segregation had occurred. The frequency of appearance of each chloroplast type differed according to the species origin of the chloroplasts. Chloroplasts from N. undulata competed much better than those from N. tabacum; N. suaveolens somewhat better than N. tabacum; and N. glauca about equally with N. tabacum. These results are compatible with an interpretation that equal frequency of appearance of chloroplast type among the regenerated plants occurs if the chloroplast DNAs of the parents are similar, whereas a bias of chloroplast type appears among the regenerated plants when the chloroplast DNAs are different. The appearance of aberrations in stamen development resembling the cytoplasmic male-sterile parental types was infrequent among the hybrid plants in all three crosses. Thus sterility factors were generally overcome by fertility factors following somatic hybridization.

Valine resistant plants derived from mutated haploid and diploid protoplasts of Nicotiana sylvestris and N. tabacum

Protoplasts were derived from haploid and diploid Nicotiana sylvestris and N. tabacum. Exposure of the protoplasts to mutagenic doses of ultraviolet (U.V.) radiation prior to two selection rounds in the presence of 4 mM (or 5 mM) and 8 mM of valine, respectively, was required to obtain cell lines with persistent valine resistance. Such lines were obtained from haploid and diploid N. sylvestris protoplasts as well as from haploid protoplasts of N. tabacum but not from (1.8 × 10(7)) diploid N. tabacum protoplasts. The ratio between number of verified valine-resistant cell lines and the initial number of U.V. exposed protoplasts enabled the estimation of the following order of mutation frequency: haploid N. sylvestris > haploid N. tabacum > diploid N. sylvestris. Plants which retained the valine resistance and transmitted it to their sexual progeny were derived from the resistant cell lines.

Cytoplasmic hybridization in Nicotiana: mitochondrial DNA analysis in progenies resulting from fusion between protoplasts having different organelle constitutions

Our previous studies indicated that fusion products with one functional nucleus but organelles of the two fusion partners (i.e. heteroplastomic cybrids) could be obtained by fusing X-irradiated (cytoplasmic donor) with non-irradiated (recipient) Nicotiana protoplasts. The present report deals with the analysis of mitochondria in cybrid populations resulting from the fusion of donor Nicotiana tabacum protoplasts with recipient protoplasts having a N. Sylvestris nucleus but chloroplasts of an alien Nicotiana species, and exhibiting cytoplasmic male sterility. The two fusion parents showed significant differences in restriction patterns of their chloroplast and mitochondrial DNA. Four groups of cybrid plants were obtained by this fusion. All had N. sylvestris nuclei but contained either donor or recipient chloroplasts and had either sterile or fertile anthers. There was no correlation between anther fertility and chloroplast type. The mitochondrial DNA restriction patterns of sterile cybrids were similar to the respective patterns of the sterile fusion partner while the mitochondrial DNA restriction patterns of the fertile cybrids were similar to the respective patterns of the fertile fusion partner. The results indicate an independent assortment of chloroplasts and mitochondria from the heteroplastomic fusion products.

Somatic hybridization in Nicotiana: Segregation of organellar traits among hybrid and cybrid plants

Protoplasts from a nitrate reductase-deficient mutant of Nicotiana tabacum L. were fused with protoplasts from a stamen-less, cytoplasmically malesterile cultivar of tobacco containing the cytoplasm from N. suaveolens Lehm. Plants were regenerated from the fused protoplasts and characterized with respect to stamen development, chromosome number, and chloroplast composition. Of 29 regenerated plants, stamen production was restored in 26 plants and pollen production in 22. One plant was male sterile and two plants have never flowered. Analysis of the electrophoretic mobility of ribulose-1,5-bisphosphate carboxylase (RuBPcase) showed that 19 of the plants contained RuBPcase of the N. suaveolens type, six plants contained enzyme of the N. tabacum type, and four plants contained both types. Analysis of resistance to tentoxin in seedlings from 20 of the plants demonstrated that 14 had N. suaveolens-type chloroplasts, three had N. tabacum type, and three contained both types. Many of the plants which produced stamens and pollen still contained chloroplasts of the N. suaveolens type. Thus, the trait of cytoplasmic male sterility in tobacco is not an expression of the type of chloroplast genetic material.

Chloroplast transfer in Nicotiana based on metabolic complementation between irradiated and iodoacetate treated protoplasts

Protoplasts of a light sensitive plastome mutant of Nicotiana tabacum (2 n=48) were irradiated and fused with iodoacetate-treated Nicotiana plumbaginifolia (2 n=20) protoplasts. Treated parental protoplasts were unable to divide. Metabolic complementation, however, helped the recovery of interspecific fusion products which survived and formed calli. Altogether 40 clones were investigated. N. plumbaginifolia plants were obtained in 15 clones (38%), somatic hybrids in 23 clones, and both types of regenerates were found in 2 clones. Irradiation therefore significantly increased the frequency of segregant formation with the non-irradiated N. plumbaginifolia nuclei (the frequency was 1.4% in the absence of irradiation). Regenerated plants in most cases (31 out of 34) contained chloroplasts from the irradiated parent. In 6 clones plants were obtained with both types of chloroplast. Thus, irradiated N. tabacum chloroplasts had an improved chance of dominating the heterokaryonderived cells, many of which contained N. plumbaginifolia nucleus. The system described should be generally applicable for the transfer of chloroplasts without the use of selectable genetic markers.

Streptomycin resistant and sensitive somatic hybrids of Nicotiana tabacum + Nicotiana knightiana: correlation of resistance to N. tabacum plastids

Protoplasts of Nicotiana tabacum SRI (streptomycin resistant) and of Nicotiana knightiana (streptomycin sensitive) were fused using polyethylene glycol treatment. From three heterokaryons 500 clones were obtained. From the 43 which were further investigated, 6 resistant, 3 sensitive, and 34 chimeric (consisting of resistant and sensitive sectors) calli were found. From eight clones, a total of 39 plants were regenerated and identified as somatic hybrids. Chloroplast type (N. tabacum = NT or N. knightiana = NK) in the plants was determined on the basis of the species specific EcoRI restriction pattern of the chloroplast DNA. Regenerates contained NT (13 plants) or NK (15 plants) plastids but only the plants with the NT chloroplasts were resistant to streptomycin. This finding and our earlier data on uniparental inheritance points to the chloroplasts as the carriers of the streptomycin resistance factor.