Somatic embryogenesis of Merwilla plumbea (Lindl.) Speta

Abstract

A simple and efficient system was developed for rapid somatic embryogenesis from leaf explants of Merwilla plumbea, a traditional but threatened medicinal plant in South Africa. Friable embryogenic callus (FEC) was obtained from leaf explants on embryogenic callus induction medium containing agar-solidified Murashige and Skoog (MS) salts and vitamins, 8.3 μM picloram, 2.3 μM thidiazuron (TDZ) and 20 μM glutamine. FEC was subsequently incubated in embryogenic callus proliferation medium containing 4.5 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 4.1 μM picloram for 7 days before it was transferred to liquid somatic embryo medium (SEML) containing MS medium supplemented with 0.4 μM picloram and 0.9 μM TDZ. In SEML supplemented with 150 mg L−1 haemoglobin, 5.4–35.6 somatic embryos per settled cell volume of 500 mg FEC were obtained. These embryos were at globular to cotyledonary developmental stages. Embryo maturation, germination and plant formation rate was 94.4% following transfer of SEs to half-strength MS medium supplemented with 1.4 μM gibberellic acid. Plantlets transferred into soil acclimatized in the misthouse and established successfully in the greenhouse (100%). This is the first report on induction of Merwilla plumbea somatic embryogenesis. The protocol developed offers controlled vegetative propagation by alleviating extinction threats, ensures germplasm conservation and provides a system for physiological, biochemical, molecular and cellular studies of embryo development.