Origin of Adventitious Shoots Regenerated from Cultured Tobacco Leaf Tissue

Leaf discs from Nicotiana tabacum L., N. glauca Grahm., and a series of interspecific periclinal chimeras were cultured on Murashige and Skoog (MS) medium containing either 2.5 mg/1 6-benzylaminopurine(BA) or 3.0 mg/16-furfurylaminopurine (kinetin). Most shoots regenerated from chimeral leaf discs were non-chimeral but 51 of 658 shoots were chimeral. The histogenic composition of plants regenerated from leaf discs of periclinal chimeras indicated that any cell layer in a leaf can be the ultimate source of shoots, and that shoots can be multicellular in origin. Certain periclinal arrangements were recovered more frequently and their chimeral nature was more stable during subsequent shoot growth. While N. tabacum leaf discs regenerated shoots on MS medium supplemented with either BA or with kinetin, N. glauca leaf discs did not form shoots on the medium containing kinetin. However, chimeras which possessed cells of both species arose on medium containing BA or kinetin, indicating that the morphogenetically competent (i.e., able to produce shoots in culture), N. tabacum cells either interacted with N. glauca cells leading to their competence or incorporated non-competent N. glauca cells into nascent shoot apical meristems.