Thidiazuron-induced shoot-bud formation on root segments of Albizzia julibrissin is an apex-controlled, light-independent and calcium-mediated response

Root segments or entire roots of Albizziajulibrissin formed shoot-buds; the former were more responsive thanthe latter. The regeneration capacity of root segments increased with anincreasing distance from the meristem. Shoot regeneration on N₆mineral formulation required either a cytokinin (BAP) or thidiazuron (TDZ); thelatter was more effective than the former, inducing a higher number of shoots ata low concentration (0.1 M) in the light as well as in thedark. The frequency of shoot formation was reduced when the auxin inhibitorsmaleic hydrazide (MH) or triiodobenzoic acid (TIBA) were included, indicating anindirect role of auxin in shoot morphogenesis. Inhibitors of calcium uptake(lanthanum) and calmodulin, trifluoperazine (TFP) or chlorpromazine (CPZ) atvery low levels, resulted in inhibition to reduction in frequency of shootmorphogenesis. This indicates that TDZ-induced shoot formation may be acalcium-mediated response. Increasing the level of calcium in the medium did notpromote shoot formation in the presence of TDZ (0.1 M). At areduced level of calcium, which was ineffective in the presence of low TDZ (0.1M), shoot-buds appeared when the concentration of TDZ wasraised to 1.0 M. This provides indirect evidence that TDZmodulates the tissue level of calcium needed for shoot formation.