A cell line of Nicotiana sylvestris with resistance to kanamycin and streptomycin

Lincomycin resistance, a new type of maternally inherited mutation in Nicotiana plumbaginifolia

Lincomycin resistant cell lines were screened in monoploid (X = 10 chromosomes) protoplast cultures of Nicotiana plumbaginifolia. Lincomycin is an inhibitor of protein synthesis on plastid ribosomes and normally inhibits greening of cultured cells on RMOP medium. The LR400 line was isolated by its ability to form a green callus on selective medium (RMOP medium containing 1,000 µg ml(-1) lincomycin hydrochloride). Diploid plants regenerated from this line inherited the resistance maternally. The LR400 line is cross-resistant to cleocin (clindamycin), but is sensitive to streptomycin.

Prevention of pink-pigmented methylotrophic bacteria (Methylohacterium mesophilicum) contamination of plant tissue cultures

Pink-pigmented facultative methylotrophic bacteria (PPFMs) have been found on the surfaces of leaves of most plants tested. We found PPFMs on the leaf surfaces of all 40 plants (38 species) tested and on soybean pods by pressing onto AMS medium with methanol as the sole carbon source. The abundance ranged from 0.5 colony forming unit (cfu) /cm(2) to 69.4 cfu/cm(2) on the leaf surfaces. PPFMs were found in homogenized leaf tissues of only 4 of the species after surface disinfestation with 1.05% sodium hypochlorite and were rarely found in cultures initiated from surface disinfested Datura innoxia leaves or inside surface disinfested soybean pods. Of 20 antibiotics tested for PPFM growth inhibition, rifampicin was the most effective and of seven others which also inhibited PPFM growth, cefotaxime should be the most useful due to the expected low plant cell toxicity. These antibiotics could be used in concert with common surface sterilization procedures to prevent the introduction or to eliminate PPFM bacteria in tissue cultures. Thus, while PPFMs are present on the surfaces of most plant tissues, surface disinfestation alone can effectively remove them so that uncontaminated tissue cultures can be initiated in most cases.

The toxicity of antibiotics to plant cell cultures

We have examined the toxicity of over twenty antibiotics to protoplast-derived cells of Nicotiana plumbaginifolia. The least toxic antibiotics are the betalactams: ampicillin, carbenicillin and the cephalosporins can be used to provide broad spectrum antimicrobial activity without significant toxicity to plant cells. Similar broad spectrum activity can also be obtained by combining rifampicin and trimethoprim. Other antibiotics which may be useful are erythromycin and colistin. The aminoglycosides are not recommended.

Isolation of somatic hybrids by cloning Nicotiana heterokaryons in nurse cultures

Fusion of Nicotiana knightiana Goodsp. and kanamycin resistant Nicotiana sylvestris Speg. et Com. protoplasts was induced by polyethylene glycol treatment. Heterokaryons were isolated by micropipette and transferred to nurse cultures of albino cells. Colonies originating from the heterokaryons could subsequently be distinguished by their green colour. The somatic hybrid nature of four such colonies was confirmed by isoenzyme pattern, kanamycin resistance and restored morphogenic potential. An additional kanamycin resistant line with characteristic Nicotiana knightiana isoenzymes was also found indicating that the drug resistance in the kanamycin resistant parent is under cytoplasmic control.