Somatic Embryogenesis in Catharanthus Roseus: Proteomics of Embryogenic and Non-embryogenic Tissues; and Genome Size Analysis of Regenerated Plant

Abstract

AbstractThe asexual, non-zygotic (somatic) embryogenesis was reported over 60 years ago. It is a unique process in which somatic cell transforms into embryo in cultured condition affirming cellular totipotency. Since its first report, somatic embryogenesis has been noted in different plant genera of a dicot, monocot, and lower fern groups. In the present chapter, an attempt has been made in describing somatic embryogenesis and its current status in periwinkle, Catharanthus roseus—an immensely important medicinal plant. The plant has anticancerous properties, the yield of alkaloids specific to this disease is however low and needs enrichment. The early embryogenic cells could serve as an important tissue for generating new cell lines with improved yield and related traits. Here, the influence of explants, the involvement of plant growth regulators, and the role of other regulating factors in establishing Catharanthus embryogenic tissues are discussed. The somatic embryo development, structure, progress, i.e., maturation, germination of embryo are also discussed with the help of Scanning Electron Microscopic method. The secondary somatic embryogenesis cycle, the embryo irregularities, and the role of protoplast culture in somatic hybridization is briefly deliberated taking Catharanthus as an example. Liquid overlaying at varying levels are described of which 0.50 ml overlaying on solid medium improved embryogenic growth and embryo number significantly. Successful artificial seed production, storage at low temperature, and plant regeneration are discussed by optimizing sodium alginate (2.5%) and calcium chloride (100 mM) solution. The proteomic approach has recently been exploited to investigate non-embryogenic, embryogenic tissues, embryo development, and other events at molecular level. In Catharanthus, over 1000 new proteins were identified from embryogenic callus, which was absent in non-embryogenic tissues. Some important proteins identified at various stages of embryogenesis are catalase, glutathione S transferase, superoxide dismutase, heat shock protein 70 (HSP70), HSP 90, and cytochrome C. Conservation of embryogenic tissues is important as it produces embryos and plantlets continuously. The cryopreservation protocol of Catharanthus is discussed by mentioning the role of osmotica, various cryoprotective agents, and the exposure of dehydration. Somatic embryo regenerated plants are true to type when developed directly on explant, but various types of variations are noted in plants developed from callus, suspension, and similar other differentiated tissues. In Catharanthus, the genome size or the 2C DNA of somatic embryo regenerated plant was noted to be 1.516 pg, which is similar to field grown plant DNA. No alteration in genome size was noted although the plants were produced through callusing. All this accumulated information on Catharanthus will be very valuable in practical and basic applications as it broadens the knowledge of cellular differentiation and dedifferentiation processes; at the same time, the methodology will augur fast multiplication of raw materials for the synthesis and enrichment of alkaloids.KeywordsCryopreservationGenome sizePlant growth regulatorsProteomicsProtoplastSignalingSomatic embryoSynthetic seed