ABSCISIC-ACID CONTROLS DORMANCY DEVELOPMENT AND BULB FORMATION IN LILY PLANTLETS REGENERATED IN-VITRO

Plantlets of lily regenerated in vitro from scale explants consist of scales and leaves from which the base of the petiole has swollen to a scale. Fluridone, an inhibitor of ABA-synthesis, applied during cultur e in vitro, inhibited the swelling of the petioles and promoted leaf f ormation. At high fluridone concentrations (10 or 13 muM), swelling wa s completely blocked, and plantlets consisted of leaves only. Addition of ABA during the regeneration in vitro had the opposite effect and r esulted in plantlets with scales only. When applied simultaneously wit h fluridone, ABA nullified the effect of fluridone. This demonstrates that bulb formation in lily is under the control of ABA. Lily plantlet s regenerated in vitro on scale explants at 20 or 25-degrees-C were ha rvested after 11 weeks, and the leaves were removed from the bulblets. The bulblets were dormant and required a cold treatment to achieve ra pid emergence after planting in soil. Fluridone added during the cultu re in vitro prevented the development of dormancy, and the bulblets di d not require a cold treatment. The effect of fluridone was nullified by simultaneous addition of ABA. Bulblets harvested after 6 weeks of c ulture at 20-degrees-C had not yet developed dormancy. Bulblets regene rated at 15-degrees-C were only slightly dormant. In both types of bul blets, it is unlikely that the lack of dormancy was due to low ABA-lev els since addition of ABA did not affect the dormancy status. These da ta indicate that the level of endogenous ABA and an unknown additional factor play major roles in the development of dormancy.