Critical ethylene exposure for Hibiscus rosa-sinensis is dependent on an interaction between ethylene concentration and duration

Experiments were designed to test the effects of ethylene on Hibiscus rosa-sinensis, and to define the critical level of ethylene exposure to elicit a response. Plants were exposed to 72 h of darkness at 18 degrees and 19 degrees C in two experiments respectively, and exposed to 0.05, 0.1, 1.0 and 5.0 mu l l(-1) ethylene for 6, 12, 24 and 72 h during the dark period. Following exposure to ethylene, the plants were placed in a postproduction evaluation room. The abscission of buds and leaves in response to ethylene was dependent on duration of exposure and concentration of the hormone. The buds showing colour were the most ethylene-sensitive parts of the plant, followed by the green buds and finally the leaves. At low ethylene exposures, the abscission response was delayed. Hibiscus rosa-sinensis was found to be very sensitive to ethylene, e.g. there was an extensive abscission of buds after ethylene exposures of 0.05 mu l l(-1) for 24 h. In addition to the ethylene response, extensive bud abscission was caused by darkness or low light levels.