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In order to clarify the process of protocorm-like bodies(PLB) formation and development of shoot apex explant with two leaf primordia in vitro as related to auxin(NAA) and cytokinin(BA), shoot apex explants were morphologically and hislochemically observed under light microscope and microspectrophotometer, respectively. Shoot apices of Cymbidium × Saxanami `Harunoumi´ were cultured for 35 days on solid medium of Murashige and Skoog(1962). In the activities of explant height, leaf elongation, leaf differentiation, and PLB formation, 0.1ppm BA was enhanced, but 0.5ppm NAA was inhibited. In course of time, size of shoot apical dome of explant was smalled and activity of cell division in shoot apical meristem of explant was unactivated. In region of definite PLB formation, activity of cell division was highest in epidermal cell of axillary. Epidermal cells of axillary were divided anticlinally and other corpus cells were divided anticlinally and periclinally at the same time. Nuclear DNA contents in epidermal cells of axillary without exogenous growth regulators were 2C to 4C.
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