Somatic hybridization in Petunia: A male sterile cytoplasmic hybrid

Reciprocal transfer of male sterile and normal plasmons in Petunia

The goal in this experiment was to achieve direct plasmon transfer via cell fusion. Two lines were used - a normal fertile line of P. hybrida, and a cytoplasmic male sterile (cms) line with the nuclear background of P. parodii. Two plants phenotypically similar to the original male sterile line were developed from protoplasts, but instead of being cms they were male fertile. On the other hand, two plants typical of the original normal line developed from protoplasts, but they were cms instead of fertile. Chromosome counts were done and in all cases the expected diploid number (=14) was found. Genetic analysis showed that sorting out of cms and fertile segregants was evident in the first and second backcross of the cms cybrids. The fertile type cybrids were stable fertile for several generations of selfing and proper backcrossing. These results are discussed in the light of an earlier fusion experiment in which these two parental lines were involved.

Somatic hybridization between male sterile Nicotiana tabacum and N. glutinosa through protoplast fusion

Protoplasts derived from suspension cultured cells of cytoplasmic male sterile Nicotiana tabacum (N. debneyi cytoplasm) and of fertile N. glutinosa were fused with the aid of polyethylene glycol (PEG). Out of 1,089 colonies developed from PEG-treated protoplasts, 29 restored whole plants.A somatic hybrid plant was selected on the basis of isoelectrofocusing analysis of Fraction I protein in leaves of regenerated plants. A newly created hybrid contained small subunits of both parents but only a N. glutinosa type large subunit.Male sterile character was conserved in a hybrid plant while leaf morphology was intermediate between the parents. By tobacco mosaic virus infection tests, the hybrid's leaves showed resistant symptoms, hypersensitive local lesions, which were due to N. glutinosa nuclear genome expression.

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.

Somatic hybridization in Petunia : Part 2: heteroplasmic state in somatic hybrids followed by cytoplasmic segregation into male sterile and male fertile lines

Two types of cytoplasmic hybrids were obtained by protoplast fusion. These contained either one or the other original parental nucleus and heteroplasmon, a mix of plasmons inducing cytoplasmic male sterility and fertility. In subsequent generations, following selfing, stable male sterile and male fertile lines segregated from single fertile cytoplasmic hybrid plants. These data demonstrated the existence of a heteroplasmic state in the somatic hybrids and the occurrence of cytoplasmic segregation of the heteroplasmon into homoplasmons following the first and the second meiotic cycles.

Progeny analysis of the interspecific somatic hybrids: Nicotiana tabacum (CMS) + Nicotiana sylvestris with respect to nuclear and chloroplast markers

The progeny of a fusion experiment involving N. sylvestris protoplasts and X-irradiated protoplasts of the cytoplasmic male sterile 'Line 92' (N. tabacum nucleus and alien, male-sterility inducing, cytoplasm) were analyzed. Three groups of somatic hybrid plants resulted: Type A, Type B-1 and Type B-2. These as well as their androgenic progenies and the progenies resulting from their pollination with N. tabacum or N. sylvestris were followed with respect to several nuclear and cytoplasmic traits. Those controlled by the nuclear genome were plant and flower morphologies; those controlled by genetic information in the cytoplasm were tentoxin sensitivity (affecting the coupling factor of chloroplast ATPase), the large subunit of ribulose bisphosphate carboxylase and the restriction endonuclease pattern of plastid DNA. A further cytoplasmic trait investigated (exact site of genetic control not known) was male sterility. The examinations of the somatic-hybrid groups and their respective progenies indicated that: Type A plants have N. sylvestris nuclei and 'Line 92' plastids; Type B-1 plants also have 'Line 92' plastids but their genome is composed of N. sylvestris and N. tabacum nuclei; Type B-2 plants with impaired male fertility had N. sylvestris plastids and N. sylvestris nuclei.