Histological studies on somatic embryogenesis in rice (Oryza sativ L.)

Rice (Oryza sativa) embryogenic calli were obtained from mature zygotic embryos culture using two varieties of rice, Sakha 101 and Sakha104 on Murashige and Skoog (1962 ) medium supplemented with 1mg/l, 2mg/l and 3mg/l 2,4- dichlorophenoxy acetic acid. The results indicated that the best medium was that containing 3mg/l. 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, each with a dense cytoplasm and a prominent nucleus and nucleolus, whereas the inner cell layer is composed of large cells with small nuclei and large vacuoles. These embryogenic cells underwent a series of organized divisions and formed the proembryo with a well-defined protodermis. At 20 days after initiation of culture, these proembryos continued a series of organized divisions and gave rise to globular somatic embryos which are delimited by a well-defined layer of epidermal cells with conspicuous nuclei. These somatic embryos had no apparent vascular connection with the mother tissue and had a suspensor. After ten days of culture on regeneration medium, globular somatic embryos developed into heart-shaped somatic embryos, which consisted of cells with prominent nuclei and dense cytoplasm. After 15 days of culture on regeneration medium torpedo-shaped somatic embryos were observed. Then, after 25 to30 days, it turned into a monocotyledon form.