Influence of petiole and lamina on adventitious shoot initiation from leaf explants of Paulownia fortunei.

Adventitious shoot bud differentiation occurred preferentially from the petiolar cut ends of leaf explants of Paulownia fortunei cultured on Murashige and Skoog medium supplemented with 4 μMα-naphthaleneacetic acid and 20 μM benzyladenine. The details of plantlet regeneration and successful transplantation to soil have been reported earlier. We now show that besides medium supplementation with auxin and cytokinin, the presence of lamina and petiole in the explant influence shoot bud induction. Explants with the basal half of the lamina and the entire petiole were much more responsive than those with whole lamina and petiole. A dual-culture-medium technique which permitted incubation of the two ends of excised petioles under two different phytohormone regimes was devised. Our data suggest that some of the diffusible factors from the lamina may be phytohormones, and that the establishment of an endogenous phytohormone gradient in the explants may affect shoot bud differentiation in this culture system.