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Some antibiotics mimic plant hormones on cell growth and plant regeneration. Cefotaxime and carbenicillin were tested in American elm for induction of embryogenesis from cotyledonary explants, which normally show organogenesis. Cotyledons from 1-week-old in vitro germinated seedlings were placed on a shoot regeneration medium (a modified MS medium containing 15 μ M BA, B5 vitamins and 0.3% gelrite) with various levels of cefotaxime and carbenicillin. One hundred percent of explants showed embryogenesis in the medium supplemented with 125 μg/ml cefotaxime; 75% explants regenerated somatic embryos in medium with 500 μg/mg carbenicillin; and only 50% explants produced somatic embryos in the medium with both of these antibiotics. In control medium without antibiotics, 100% explants regenerated shoots, instead of somatic embryos. Further studies are necessary to determine the nature of these antibiotics on shifting developmental pathways and their stimulatory effect on embryogenesis from American elm cotyledons.
Leaf discs of Salpiglossis sinuata L. were infected with disarmed Agrobacterium tumefaciens strain LBA 4404 carrying β-glucuronidase (GUS) gene and kanamycin resistance. Plantlets were regenerated from the leaf discs cultured on Murashige and Skoog (MS) medium supplemented with 10 μM kinetin and 1 μM naphthaleneacetic acid (NAA) plus 300 mg/liter kanamycin. The plantlets were then rooted on the MS medium containing the same concentration of kanamycin plus 2 μM NAA without kinetin. The histochemical assay showed that the regenerated plants were GUS positive. A Southern blot test is underway to determine the stability of the transferred genes in the regenerated plants.