Maturation of Yellow-Poplar Somatic Embryos

Abstract

Since somatic embryogenesis in yellow-poplar (Liriodendron tulipifera) was first reported, a major problem with the system has been the very low conversion frequencies of somatic embryos. Although large numbers of embryos could be produced in liquid medium, conversion percentages were even lower than for those differentiated on solid medium, where conversion averaged less than 1 percent. Proembryogenic masses (PEMs) removed from auxin-supplemented medium and placed in hormone-free medium generally produced malformed and clustered somatic embryos that were asynchronous in their development and that failed to mature properly, retaining fused or malformed cotyledons, even though radicles would elongate. To promote production of somatic embryos capable of conversion to plantlets, we tested physical and chemical treatments on embryogenic suspension cultures. Production of synchronous, mature, well-formed embryos was promoted by fractionating embryogenic suspensions on sieves and culturing in medium supplemented with abscisic acid (ABA). High levels of sucrose in the medium could substitute for ABA to a certain extent in aiding embryo maturation. However, conversion of the embryos was inhibited once they were transferred to solid medium. A modification of this technique, in which PEMs were plated on physical supports on solid medium immediately following fractionation, raised average conversion frequencies for mature embryos to over 70 percent.