Adventitious shoot regeneration from vegetative shoot apices in pear and putative role of cytokinin accumulation in the morphogenic process

Adventitious shoot regeneration was obtained from callus produced from main vegetative apices of pear of in vitrogrown shoots of Italian cultivars Spadona and Precoce di Fiorano and wild pear genotypes ISF54 and ISF61. The highest morphogenetic response was obtained on a medium containing 8.8 μM 6-benzyladenine, 1.0 μM α-naphthaleneacetic acid and 250 mg l−1cefotaxime. The explants were maintained for 30 days in darkness and then transferred to an auxin-free medium and to the light. Histological studies revealed that the new vegetative buds originated from callus that completely altered the morphology of the explant tissues by the 30th day of culture. The in situ localisation of cytokinins, performed using antibodies with marked specificity against zeatin (Z) and isopentenyladenine, revealed an accumulation of Z in the cambiform cells of the leaf primordia and in the shell zone of the new forming buds showing a primary role of this cytokinin in cell differentiation of in vitro pear organogenesis.