Reversal of Induced Dormancy in Lettuce by Ethylene, Kinetin, and Gibberellic Acid

The germination of lettuce seeds (Lactuca sativa L., cv. Premier Great Lakes) was significantly inhibited by high temperature (32 C), 0.1 mM abscisic acid or 0.4 M mannitol. Ethylene (16 mul/1 of air) partially reversed the dormancy induced by all three inhibitors but only in the presence of 1 mM gibberellic acid (GA) or light. Neither ethylene plus GA nor ethylene plus light were able to promote germination when thermal inhibition was imposed at 36 C. Addition of 0.01 mM kinetin to the ethylene plus GA or light reversed thermodormancy at 36 C. The dormancy imposed by abscisic acid was also reversed by kinetin. Kinetin was unable to reverse the osmotic dormancy imposed by mannitol. The reversal of osmotic dormancy by ethylene or ethylene plus GA was actually inhibited by kinetin but only in the light. Kinetin apparently stimulates cotyledonary growth in the presence of light, and this growth may compete for certain metabolites critical to radicle growth and subsequent germination. Kinetin and ethylene, as demonstrated primarily in the thermodormancy at 36 C and in osmotic dormancy, appear to regulate a common event(s) leading to germination but through mechanisms unique to each respective growth regulator. The regulation of germination by ethylene is absolutely dependent upon an interaction with GA and/or light.