Factors affecting shoot regeneration from zygotic embryo and seedling explants of Cycas revoluta thunb

Summary Adventitious shoot induction from zygotic embryo and seedling explants of Cycas revoluta was studied, with reference to both nitrogen formulation of the medium and light. The presence of nitrate as a sole source of nitrogen in Klimaszewska and Keller (KK) medium did not promote shoot induction; on the other hand, shoot induction was promoted by the use of ammonium-containing media, i.e., Schenk and Hildebrandt (SH) and Murashige and Skoog (MS). In the case of zygotic embryos, the percentage of responding explants and the number of regenerated shoots were significantly higher on SH medium than on MS medium. With seedling explants, shoot induction was not affected by the use of SH medium versus MS medium. Photoperiod also influenced bud formation and development. The absence of light during shoot induction stimulated callus formation and very few differentiated shoots. Shoot induction from zygotic embryos was positively affected by the application of 4- and 8-wk photoperiod exposures, the combination SH medium/8-wk photoperiod exposure giving the best results in terms of shoot induction and development. Rooting of shoots was improved by their culture in medium containing NAA.