Protoplast-derived streptomycin resistant plants of the forage legume Onobrychis viciifolia Scop. (sainfoin)

Induction of streptomycin-resistant plantlets inCapsicum annuum L. through mutagenesisin vitro

Streptomycin resistant shoots were regenerated from mutagenised (ethylemethane sulphonate treated) cotyledon explants ofCapsicum annuum Cv G4. Streptomycin resistant shoots developed from green (unbleached) sectors of the cotyledons. Reciprocal crosses betweeen streptomycin resistant and sensitive plants have shown a non-mendelian transmission. Such mutant plants should be useful in designing biochemical selection schemes to recover somatic hybrids and cybrids ofC. annuum.

Mutations conferring lincomycin, spectinomycin, and streptomycin resistance in Solanum nigrum are located in three different chloroplast genes

A number of Solanum nigrum mutants resistant to the antibiotics spectinomycin, streptomycin and lincomycin have been isolated from regenerating leaf strips after mutagenesis with nitroso-methylurea. Selection of streptomycin- and spectinomycin-resistant mutants has been described earlier. Lincomycin-resistant mutants show resistance to higher levels of the antibiotic than used in the initial selection, and in the most resistant mutant (L17A1) maternal inheritance of the trait was demonstrated. The lincomycin-resistant mutant L17A1 and a streptomycin plus spectinomycin resistant double mutant (StSp1) were chosen for detailed molecular characterisation. Regions of the plastid DNA, within the genes encoding 16S and 23S rRNA and rps12 (3') were sequenced. For spectinomycin and lincomycin resistance, base changes identical to those in similar Nicotiana mutants were identified. Streptomycin resistance is associated with an A-->C change at codon 87 of rps12 (converting a lysine into a glutamine), three codons upstream from a mutation earlier reported for Nicotiana. This site has not previously been implicated in streptomycin resistance mutations of higher plants, but has been found in Escherichia coli. The value of these mutants for studies on plastid genetics is discussed.

EMS-induced streptomycin resistance in Solanum melongena

Streptomycin-resistant mutations were induced in Solanum melongena by exposing seeds to ethyl methane sulphonate (EMS). Seed mutagenesis resulted in a high frequency of chlorophyll-deficient mutations and a low frequency of resistant shoots, both of which retained their resistance on subsequent testing. Reciprocal crosses between streptomycin-resistant and -sensitive plants showed a non-Mendelian transmission of the resistance trait. Streptomycin resistance is the first selectable and maternally inherited organelle marker described in brinjal.

Influence of ploidy on plastome mutagenesis in Nicotiana

A clear influence of ploidy was observed on the frequency of both spontaneous and nitroso-methylurea (NMU) induced, streptomycin-resistant, adventitious shoots developing on leaf explants of Nicotiana tabacum and N. plumbaginifolia. At nearly all NMU levels employed a significantly higher yield of resistant shoots was obtained from haploid compared with diploid leaf strips. At 1 mM NMU the differences were not significant and were absent when a high (1000 mg/l) selective concentration of streptomycin sulphate was used. The influence of ploidy is discussed in relation to the possible effect of plastome copy number on mutagenesis and sorting out of resistant plastids.

Isolation and characterization of streptomycin-resistant mutants in Nicotiana plumbaginifolia

Streptomycin-resistant colonies were isolated from protoplast cultures of haploid Nicotiana plumbaginifolia based on their ability to green in medium containing 1 mg/ml streptomycin sulfate. The frequency of resistant colonies was 0.9×10(-5) in nonmutagenized culture, and increased ten-fold following treatment of culture with 10 μg/ml N-methyl-N'-nitro-N-nitrosoguanidine. Of a total of 52 resistant clones isolated, 2 gave rise to haploid, 15 to diploid, and 3 to tetraploid plants upon transfer of calli to differentiation medium. Leaf-segment and protoplast assays showed that all diploid regenerates were resistant to streptomycin but sensitive to chloramphenicol, kanamycin, lincomycin, neomycin, and spectinomycin. Plants in most diploid clones were fertile and able to set seeds when self-fertilized and crossed reciprocally to wild-type plants. Inheritance of streptomycin resistance was studied in the diploid clones and, without exception, the resistance was transmitted maternally. Comparative studies of the ultrastructure of organelles and protein synthesis in isolated chloroplasts between wild-type and resistant clones in the presence of streptomycin suggest that streptomycin resistance is controlled by chloroplasts.