Somatic embryogenesis in Phlox paniculata — histological analysis

Abstract

In vitro regeneration and histological analysis of somatic embryogenesis derived from in vitro leaves were assessed in Phlox paniculata L. The explants were incubated on Murashige and Skoog medium containing 2.26–4.52 μM 2,4-dichlorophenoxyacetic acid (2,4-D) with or without 0.89 μM benzyladenine supplemented with 3% or 9% sucrose and vitamins. The intact leaf blades were cultured in the dark at temperature 22 ± 2◦C. Two Phlox cultivars showed significantly higher regeneration capacity in the in vitro conditions when the cultivation media have been supplemented with 2,4-D at concentrations of 4.52 μM and 3% sucrose. The effect of 2,4-D on somatic embryo induction has been enhanced in presence of cytokinin benzyladenine. In cultivars, the embryogenic structures have been created on calluses derived from leaf sections within 6–9 weeks in culture. Meristematic zones with forming embryogenic structures were mostly localized adjacent to de novo forming tracheal elements in calluses in our experiments. In the absence of tracheal elements, the embryogenic structures have been surrounded by several layers of isodiametric cells. The embryo proper and the suspensor part could be clearly distinguished on the embryogenic structures. The embryogenic potential of cultures has been very high, so that even secondary and tertiary somatic embryos were formed. Within 6–9 weeks in culture, well differentiated embryogenic structures up to torpedo stages were developed. Cultivar ‘Fuji’ exhibited slightly higher embryogenic response in culture than cultivar ‘Starfire’. The cultures maintained their embryogenic potential for about 18 months. Embryogenic structures have been able to convert to complete plants within 3 months.