Sensitivity to ethylene as a major component in the germination of seeds of Stylosanthes humilis

Physiological dormancy of scarified seeds of Townsville stylo (Stylosanthes humilis H.B.K.) is broken by ethylene. When the biosynthesis of this gas was impaired by 2-aminoethoxyvinylglycine (AVG) plus Co2+, the response to ethylene at very low concentrations was appreciable in non-dormant seeds and nil in the dormant ones. Complete inhibition of germination of non-dormant seeds occurred only when they were treated with AVG plus Co2+ under an ethylene-free atmosphere, a condition in which no trace of the gas in the atmosphere of Erlenmeyer flasks could be detected. Injection of ethylene into that system triggered germination of both dormant and non-dormant seeds, demonstrating a requirement for the gas. Non-dormant seeds were at least 50-fold more sensitive to ethylene than the dormant ones. Perception of ethylene occurred within a very short time (at most 15 min), since exposure of both dormant and non-dormant seeds to the gas, at a steeply declining concentration, sufficed to cause substantial germination.