Shoot organogenesis and plantlet regeneration from hypocotyl-derived cell suspensions of a tree legume, Dalbergia sissoo Roxb.

A complete and efficient protocol is presented for plant regeneration from cell-suspension cultures of Dalbergia sissoo Roxb., an economically importa nt leguminous tree. Factors influencing callus initiation, establishment of cell-suspension culture, callus formation from embedded microcolonies, and shoot organogenesis from suspension-derived callus were identified. Of the two different auxins tested, callus induction was better on a medium conta ining naphthalene acetic acid (NAA). The percentage of callus induction inc reased considerably when NAA at 2.0 mg l(-1) (10.8 muM) was added in conjun ction with 0.5 mg l(-1) (2.2 muM) N-6-benzyladenine (BA). Of the three diff erent explants evaluated for callus induction, hypocotyl segments were most responsive. Friable hypocotyl-derived callus from the second subculture pa ssage was used to initiate the cell-suspension culture. Optimum growth of t he cell-suspension was observed in MS medium supplemented with the same gro wth regulators as described above for callus induction, with an initial ino culum cell density of 1%. The plating efficiency of the microcolonies was g reatly influenced by harvesting time and the gelling agent used for plating . Efficiency was highest (93%) with cells harvested at their exponential gr owth phase and plated in 1.2 g l(-1) Phytagel. Shoot organogenesis from cal lus cultures was higher on a medium supplemented with a combination of BA a nd NAA than on BA alone. Seventy-one per cent of cultures exhibited shoot-b ud differentiation on a medium containing 3.0 mg l(-1) (13.3 muM) BA and 0. 5 mg l(-1) (2.7 muM) NAA. Regenerated shoots: were rooted on half-strength MS medium containing 1 mg l(-1) each of indole-3-acetic acid (5.7 muM), ind ole-3-butyric acid (4.9 muM) and indole-3-propionic acid (5.3 muM). Plantle ts were acclimated and established in soil.