Modulation of shoot formation in tobacco callus by tissue transfer between permissive and inhibitory media

Summary In an attempt to understand events involved in the cellular regulation of in vitro plant organogenesis, experiments were performed in which tobacco (Nicotiana tabacum L.) callus was transferred at different days in culture from a shoot-forming medium to a non-shoot-forming medium and vice versa. The transfers were made at key histologic stages of the shoot-forming process and known biochemical and biophysical correlates were examined. The changes in starch accumulation and disappearance supported the previously assigned functions, and could be correlated with the histologic changes that occurred in the callus after transfer at the different culture times. In contrast, the changes in respiration could not be correlated with these events. The changes in osmotic and turgor potentials after transfer showed that osmotic adjustment preceded both shoot initiation and development. This suggests that osmotic adjustment might play an important role in in vitro organogenesis. This research was supported by the Natural Sciences and Engineering Research Council of Canada grant A-6467 to T. A. T.