PLANT HORMONE EFFECT OF ANTIBIOTICS ON THE TRANSFORMATION EFFICIENCY OF PLANT-TISSUES BY AGROBACTERIUM-TUMEFACIENS CELLS

The inhibition of bacterial growth by carbenicillin and cefotaxime was demonstrated using three different Agrobacterium tumefaciens strains, LBA4404, C58 and EHA101. LBA4404 was the most sensitive strain to carbenicillin and cefotaxime. Significantly toxic effects were observed when tobacco leaf explants were grown on MS medium containing 250 mu g/ml carbenicillin and 1 mu g/ml 2,4-dichlorophenoxyacetic acid (2,4-D). The regeneration of tobacco shoots from tobacco leaf explants was decreased as the addition of carbenicillin increased from 250 mu g/ml to 2000 mu g/ml in MS medium containing 0.5 mu g/ml of 6-benzylaminopurine (BA). Interestingly, tobacco leaf explants grown on the MS medium containing carbenicillin alone up to 1000 mu g/ml did not show any toxic effects. Moreover, chemical structure comparisons revealed that carbenicillin contains auxin related structures like 2,4-D or alpha-naphthalenacetic acid (NAA), suggesting that the toxic effects of combinations of carbenicillin and 2,4-D may be due to high auxin activity levels. Further studies demonstrated that by adjusting the levels of carbenicillin and 2,4-D, the transformation efficiency of Arabidopsis thaliana ecotype Columbia and Landsberg was significantly improved from 20% to >90% using Agrobacterium-mediated transformation.