Abstract
In order to clarify the roles of auxins (IAA, NAA, and 2, 4-D), cytokinin (BA), gibberellin (GA), and abscisic acid (ABA) in organogenesis and development of excised shoot apices in vitro as related to their dimension, shoot apices of Cymbidium × Sazanami‘Haru-no-umi’were cultured on solid medium of Murashige and Skoog (1962).
Auxins caused the shoot apex explants to produce many new adventitious roots, but inhibited shoot formation. Marked increase in fresh weight of explants was caused by high concentrations of 2, 4-D, but the adventitious roots were abnormal. One tenth ppm 2, 4-D and 1.0ppm NAA enabled the explants with 6 leaf primordia to develop into single whole plants. Cytokinin caused production of many new protocorm-like bodies and shoots, but inhibited production of new adventitious roots at higher concentrations. Neither GA nor ABA was observed to influence organogenesis or development of the explants advantageously. The explants with 3 or more leaf primordia required no exogenous growth regulators for chlorophyll synthesis and organogenesis. Preferably, higher concentrations of NAA and ABA inhibited chlorophyll synthesis in the explants with 6 leaf primordia. The sources of these growth regulators in the shoot apices were discussed and located in the second pair of leaf primordia.
