Somatic embryogenesis in Stackhousia tryonii Bailey (Stackhousiaceae) : a rare and nickel-hyperaccumulating species of Central Queensland (Australia)

Stackhousia tryonii Bailey is a rare, serpentine-endemic herb that has potential for use in phytoremediation and/or phytomining, both requiring large numbers of plants to be viable. S. tryonii is difficult to propagate through seed. There is hardly any information available on its vegetative propagation. This study was undertaken to develop mature and hardened embryos which can be succussfully encapsulated and transformed into artificial seeds for storage or direct cultivation in conservation programs. Nodal segments from micropropagated plants were inoculated onto callus induction media consisting of Murashige and Skoog (MS) basal medium supplemented with auxins (2.4-D, dicamba or picloran at 0.1 0r 5 uM), cytokinins (zeatin or kinetin at 0, 0.1 or 1.0 uM) or combinations of both. After 4 weeks, cultures were transferred onto fresh MS medium containing no plant growth regulators. Callus induction occurred only when 2.4-D was used along with cytokinins. Most explants including those in control treatment produced shots. However, somatic embryogenesis occurred only when a low concentration of picloram (1 uM) was used with cytokinins. Somatic embryos failed to develop further, when maintained on plant growth regulator-free medium. Most somatic embryos (90%) germinated, producing roots but only a few produced both shoots and roots. Histological studies confirmed the induction of somatic embryos.