Research in Plant Biology, 3(5): 21-27, 2013 ISSN : 2231-5101 www.resplantbiol.com Received: 20.6.2013; Revised: 18.9.2013; Accepted: 20.9.2013 Regular Article Morphological and Histological Observation of Embryogenic Calli Derived from Immature Embryo of BRRI Dhan28 (Oryza sativa L.) Variety Md. Mahmudul Islam, Md. Enamul Haque, Shah Md. Mahbub Alam, Md. Asadul Islam, Md. Khalekuzzaman, Biswanath Sikdar* Department of Genetic Engineering and Biotechnology, Faculty of Life and Earth Science, University of Rajshahi, Rajshahi-6205, Bangladesh *Corresponding author Email: bsikdar2004@yahoo.com Somatic embryogenesis is the most common method for regeneration in rice. In vitro studies of indica rice (Oryza sativa L.) variety BRRI dhan28 was used for obtaining embryogenic calli from immature embryo culture on Murashige & Skoog medium supplemented with 2.5 mg/l dichlorophenoxyacetic acid (2,4-D) and 0.5 mg/l naphthaleneacetic acid (NAA) showed the highest percentage (91%) of callus induction. In this combination 80% embryogenic calli were formed uneven with a crisp texture, loose structure and salient multicellular structures on the surface while non embryogenic calli were compact with a smooth surface. Under microscopic observation, embryogenic cells were smaller, globular and abundant in cytoplasm with one or two big nuclei. Non embryogenic cells were little cytoplasm and few large vacuoles with no or only a small nucleus and wide intercellular spaces. Non embryogenic cells had a very low cell division capability while embryogenic cells had a high capability for cell division and continued to divide and produced somatic pro-embryos with a well–defined protodermis which could develop further through the typical globular, heart, torpedo and cotyledonary stages. Only 80% of embryogenic cells were induced high differentiation rate and developed 65 globular, 52 heart-shape, 43 torpedo and 37 cotyledonary embryos of embryogenic cells after 30 to 45 days of induction. Key words: Rice, callus, embryogenesis, morphology, histology Rice is the most important primary food source for more than a third of the world's population. Indica and japonica rice are the two major subspecies. Indica rice varieties calculate for 80% of the cultivated rice. Somatic embryogenesis is the most common method for regeneration in rice. Somatic embryogenesis is two types: one is direct somatic embryogenesis and another indirect somatic embryogenesis. Direct somatic embryogenesis is produced by induction of somatic embryos directly from pro-embryogenic cells from leaves, stem, microspores, protoplast without the proliferation of calli where as in indirect somatic embryos are produced from friable embryogenic calli.