ETHYLENE RESPONSIVENESS CHANGES IN PELARGONIUM X DOMESTICUM FLORETS

Florets of Pelargonium x domesticum L. H. Bailey respond to ethylene with rapid petal abscission. Florets become increasingly responsive to ethylene with age, with the greatest change in responsiveness occurring between the day of anthesis and 2 days later. The ethylene responsiveness coefficient (the ratio of the concentrations of ethylene giving 90% and 10% abscission) declined from 21 in 1-day-old florets to slightly greater than 1 in older florets; therefore abscission was ultraresponsive (responsiveness coefficient < 81) even in 1-day old florets. Younger florets required a higher concentration of ethylene and longer duration of ethylene exposure to induce the abscission response. Even florets aged 2-3 days after anthesis required at least 40 min of exposure to ethylene for the abscission response to occur, irrespective of the concentration.