Plant regeneration through somatic embryogenesis from suspension cultures of gherkin (Cucumis anguria L.).

Gherkin (Cucumis anguria L.) is an important highly nutrient vegetable and traditional medicinal plant. An efficient protocol for plantlet regeneration from cell suspension cultures of gherkin (Cucumis anguria L.) through somatic embryogenesis is reported here. Leaf-derived embryogenic calli were cultured on Murashige and Skoog medium augmented with 4.0 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 1.0 μM kinetin (KIN). The maximum frequency of somatic embryos (33.5%) was observed on MS medium supplemented with 2.0 μM 2,4-D for three weeks of culture. Ontogenic studies of somatic embryos revealed that the cells destined to become somatic embryos divided into spherical proembryos and then progressed to globular, heart and further differentiated properly into torpedo and cotyledonary stages within 5 weeks. Embryo development was asynchronous and strongly influenced by the 2,4-D concentration. The MS liquid medium augmented with 2.0 μM 2,4-D and 0.5 μM L-glutamine was effective to achieve high frequency of somatic embryo induction (44.5%). The cotyledonary-stage somatic embryos were transferred to MS liquid medium with no plant growth regulators to achieve complete maturation within 7 days. Lack of 2,4-D in suspensions increased somatic embryo maturation with decreased abnormalities. Sucrose was found to be the best carbon source for callus induction, embryo maturation and embryo germination. Relatively, only few numbers of embryos developed into root/shoot when transferred to 1/10 MS solid medium containing 0.5 μM abscisic acid (ABA), 2% (w/v) sucrose and 0.2% (w/v) gelrite. About 15% of somatic embryos germinated into morphologically normal fertile plants within 2 weeks. Regenerated plantlets were successfully hardened, with a survival rate of approximately 80%, and established in the field. This regeneration protocol assured successful embryo induction, maturation and plantlet conversion.