1994 Volume 63 Issue 3 Pages 663-673
Outer tissue (OT) excised from protocorm-like bodies (PLB) of Cymbidium×Thanksgiving, cultivar 'Nativity' produced PLB on hormone-free Murashige and Skoog (MS) medium and MS media supplemented with hormones. The PLB initiation from OT was earlier on hormone supplemented media compared to hormone-free MS medium. Explants showed the highest PLB formation abilitiy on the medium supplemented with 0.1 mg • liter-1 α- naphthaleneacetic acid (NAA) and 0.5 mg • liter-1 benzyl adenine (BA). On the medium of this combination, rate of cell division was high and the cell division occurred from surface to deeper tissue in the protuberance (an initial structure of PLB formed on OT explants) after 14 days of culture. OT explants turned light brown after 7 days of culture and a gray transparent protuberance was observed on the outer surface of the ex- plant after 14 days of culture. The protuberance gradually increased in size and turned into a green globular PLB after 21 days of culture. This pattern of PLB formation was similar in both hormone supplemented MS media and hormone-free MS medium. Thus it suggests that exogenous hormones have no fundamental effects on PLB formation. OT-de- rived PLB formed 100% shoot on the medium supplemented with 0.1 mg • liter-1 NAA and 1.0 mg • liter-1 BA within 8 weeks, but shoot formation was markedly suppressed on the media supplemented with NAA alone.
Histological study showed that OT segments consisted of epidermal and sub-epidermal cells, which were parenchymatous, large and vacuolated. After one week culture, all the cells of epidermis were ruptured. A small group of cells with dense cytoplasm and deeply stained nuclei was observed just below the ruptured epidermis. These cells developed into a PLB. This result showed that OT of Cymbidium PLB has ability to produce PLB directly from explants through organogenesis.