Hormone-independent callus growth of in vitro-cultured leaf sections of
E2Fa-DPa plants. A, Effect of hormone combinations on regeneration of callus,
roots, and shoots. Strips of mature leaves of 35S-GUS, -E2Fa, and
-E2Fa-DPa/H-F3D transgenic tobacco plants were cultured with 0.5×
Murashige and Skoog medium containing the indicated hormones at the given
concentrations for 4 weeks. B, Callus growth in the L-F3D line on hormone-free
medium. Leaf strips from 35S-GUS and -E2Fa-DPa/L-F3D plants were cultured with
0.5× Murashige and Skoog medium without hormones for 8 weeks. C,
Expression of cell cycle genes in leaf strips cultured with hormone-free
medium. Leaf strips from the indicated plants were cultured with 0.5×
Murashige and Skoog medium without hormones for 0 or 24 h. Expression of the S
phase (PCNA) and M phase (cyclin B and cyc29) genes
was semiquantified by RT-PCR analysis.