Efficient callus induction and plant regeneration of Lemna gibba strain 5503

In spite of the fact that Lemna gibba has an excellent potential in genetic transformation, only one strain has been transformed because of the limitation of available strains that have been optimized to regenerate efficiently in tissue culture. An axenic clone of the new strain of L. gibba was obtained from an industrial waste water lake in Egypt. The international ID 5503 was given to this new strain. 2,4-dichlorophenoxyacetic acid (2,4-D) concentration, light and frond orientation on media were examined to induce callus. Dorsal side up of the fronds was essential for callus induction. Low concentrations of 2,4-D (1-2 mg L-1) did not induce any visible callus while high concentrations (6-8 mg L-1) produced high frequency of callus induction (61-70% for light treatments and 50-65% for dark treatments). Light incubation treatments were generally superior in the frequency of callus induction especially with higher concentrations of 2,4-D (5-8 mg L-1). MS medium without cytokinins or supplemented with benzyladenine (BA) (1 mg L-1) or zeatin riboside (1 and 2 mg L-1) were examined to regenerate fronds from callus. Callus of light incubation treatments was superior to that of dark incubation treatments in regeneration with MS medium without cytokinin. Callus of dark incubation treatments was superior in regeneration with MS medium supplemented with cytokinins. One mg L-1 BA with the dark-derived treatment 6 mg L-1 2,4-D and 1 mg L-1 zeatin riboside with the dark-derived treatment 8 mg L-1 2,4-D determined highest regeneration frequency (80% each). Efficient callus induction (up to 80%) and regeneration (up to 90%) protocols were developed for the first time with the new L. gibba strain 5503. This new strain is the third L. gibba genotype that has been tested for callus induction and plant regeneration.