Regeneration of Tomato (Lycopersicon esculentum Mill.): Somatic Embryogenesis and Shoot Organogenesis from Hypocotyl Explaints Induced with 6-Benzyladenine

In vitro regeneration of plants was achieved in four cultivars of tomato (Lycopersicon esculentum Mill.). The explants were 10-mm hypocotyl sections, excised from 2-wk-old seedlings grown on Murashige and Skoog (MS) medium supplemented with or without 6-benzyladenine (BA). The hypocotyl explants were subcultured on MS medium without growth regulators or on MS media supplemented with 5, 10, 20, or 40 μM BA. Regeneration through somatic embryogenesis and shoot organogenesis occurred in explants of all treatments, even on hypocotyls from seedlings grown on basal medium and subcultured to medium without growth regulators. Explants from seedlings grown on BA-supplemented medium produced the highest frequency of regenerants when subcultured to media containing BA. In contrast, BA had an inhibitory effect on explants obtained from seedlings grown on media lacking BA. Light microscopic observations confirmed that regeneration occurred via both somatic embryogenesis and shoot organogenesis from the subepidermal cortical tissue. Developing somatic embryos were encased in a distinct protoderm, had a suspensor-like structure, and were loosely attached to the hypocotyl tissue. Somatic embryos and shoots developed into complete plants on a medium lacking growth regulators.