Direct shoot regeneration from Arabidopsis thaliana shoot apical meristems

In Arabidopsis thaliana in vitro culture, shoots were induced from the shoot apical meristem (SAM) of germinating seeds in the presence of 2,4-dichlorophenoxyacetic acid. Primary shoot primordia developed leaf-like structures, from which secondary shoot primordia were produced. Regenerated shoots were recovered when the material was transferred to a medium lacking auxin. Adventitious roots formed from a callusing basal region of the secondary shoots. The CUC1 transcription factor was expressed at the apex of the primary shoot primordium and at the boundary between the regenerated SAM and the developing leaf primordia. The DR5::GUS transgene was used to localize sites of maximum auxin occurrence. Auxin was firstly detected in the dividing cells beneath the SAM epidermis, which coincided with sites where primary shoot primordia were initiated. In the regenerated shoots, auxin response was not detected in the basal region of the stem, suggesting that the regenerating structures were shoots rather than somatic embryos. Direct shoot regeneration from the A. thaliana SAM requires a localized accumulation of auxin.