THIDIAZURON-INDUCED IN-VITRO SHOOT FORMATION FROM ROOTS OF INTACT SEEDLINGS OF ALBIZZIA JULIBRISSIN

Seedlings of silktree (Albizzia julibrissin Durrazz.) were grown in vi tro on MS-media containing B5 vitamins, 3% sucrose, 0.25% phytagel and various concentrations (0.1-10 mu M) of thidiazuron (TDZ). Addition o f TDZ to the culture medium greatly reduced shoot and root elongation but did not influence shoot production from the cotyledonary node or a pex. Within 8-10 days the seedling roots split open, formed large mass es of callus, and developed green patches which eventually grew into n ormal shoots while still within the culture medium containing TDZ at 0 .1-1.0 mu M. Such callus and shoot formation did not occur in control cultures lacking TDZ. At higher TDZ concentrations (2.5-10 mu M), the green patches formed in the callus did not further develop into shoots . Addition of other cytokinins (kinetin, benzylaminopurine, zeatin) to the culture medium also induced some shoot formation from the roots, but higher concentrations than TDZ were required to induce regeneratio n. Isopentenyladenine failed to induced shoot formation. Following exc ision and transfer to MS media with or without 4.9 mu M IBA, the shoot s induced by kinetin or benzylaminopurine rooted 4-7 days earlier than those induced by TDZ, but all excised shoots developed into normal ro oted plantlets within 3 weeks.