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Histology of somatic embryogenesis in rice (Oryza sativa cv. 5272)
Rafael Vega1, 4, Nelly Vásquez2, Ana M. Espinoza3, Andrés M. Gatica1 & Marta Valdez-Melara1
1. 2. 3. 4. Escuela de Biología, Universidad de Costa Rica, 11501-2060, San Pedro, Costa Rica. Centro Tropical de Investigación y Enseñanza (CATIE), Turrialba, Costa Rica. Centro de Investigación en Biología Celular y Molecular (CIBCM), Universidad de Costa Rica, 11501-2060, San Pedro, Costa Rica. Dirección actual: Fundación para la Innovación Tecnológica Agropecuaria, El Salvador. Received 11-X-2007. Corrected 29-VIII-2009. Accepted 04-X-2009.

Abstract: Rice (Oryza sativa cv. 5272) embryogenic calli were obtained from mature zygotic embryos culture on Murashige & Skoog (1962) medium supplemented with 2.5 mg/l 2,4- dichlorophenoxyacetic acid. Histological analysis of somatic embryogenesis revealed that after two weeks of culture of explants on the callus induction medium, somatic embryo development began with a cluster of proembryogenic cells in the peripheral region of the calli. The outer cell layer of embryogenic calli consisted of small and isodiametric cells with a dense cytoplasm and a prominent nucleus and nucleolus; whereas the inner cell layer is composed of large cells with small nucleus and large vacuole. These embryogenic cells underwent a series of organized divisions and formed the proembryo with a well-defined protodermis. Rev. Biol. Trop. 57 (Suppl. 1): 141-150. Epub 2009 November 30. Key words: Oryza sativa, rice, in vitro culture, histology, somatic embryogenesis, morphogenesis, Costa Rica.

The totipotent character of plant cells allow that any differentiated cells that retains its nucleus has the ability to regenerate an entire new plant by organogenesis or somatic embryogenesis (SE) (Reynolds 1997, Fortes & Pais 2000). SE is the developmental process by which bipolar structures that resemble zygotic embryos are developed from haploid or diploid somatic cell through an orderly