Tissue culture and Agrobacterium-mediated transformation of watercress

Adventitious shoot regeneration could be obtained from more than 80% of the calluses initiated from stem explants of watercress (Rorippa nasturtium-aquaticum) by using an induction medium and a shoot regeneration medium. The induction medium contained 1.15 μM 2,4-dichlorophenoxyacetic acid and 5 μM thidiazuron; the shoot regeneration medium was composed of 0.5 μM thidiazuron and 2.25 μM 6-benzylaminopurine. This regeneration procedure was incorporated into an Agrobacterium-mediated transformation procedure for gene transfer into watercress. Factors affecting transformation included preculture, selection agents, use of tobacco nurse cells, and the length of coculture. A transgenic line of watercress transformed with a wild-type Bacillus thuringiensis insecticidal gene, cryIIa3, was not toxic to larvae of the diamondback moth (Plutella xylostella), presumably due to premature polyadenylation of the transcript encoded by this gene in the plant.