Penicillin derivatives induce chemical structure-dependent root development, and application for plant transformation

We investigated five penicillin derivatives that are popularly used for transformation experiments with Agrobacterium rhizogenes—penicillin G, carbenicillin, ampicillin, amoxicillin and cephalexin—for their effects on the growth and morphology of Beta vulgaris, Capsicum annuum and Glehnia littoralis roots. Attention was given to the relationship between their chemical structures and functions. Ampicillin was found to stimulate root elongation but inhibit root branching, whereas carbenicillin inhibited root elongation but promoted root branching. Root cultures were also exposed to hydrolyzed products of these antibiotics—i.e. phenylmalonic acid (PM), phenylglycine and 6-aminopenicillanic acid (6-APA): PM inhibited root elongation the most, while root elongation was supported best by 6-APA. These results indicate that both the side chains and the major component of penicillin derivatives affect root development and that the nature of the side chains is responsible for the responses. Ampicillin but not carbenicillin was used in subsequent experiments described herein to eliminate bacteria and to support root growth of transformants of the recalcitrant plants.