Use of a laser-driven photoacoustic detection system for measurement of ethylene production in cymbidium flowers

A laser-based photoacoustic method was used for determination of ethylene (C₂H₄) production of emasculated orchid (Cymbidium) flowers in a flow-through system. The laser photoacoustic equipment consisted of a line-tuneable CO₂ laser in conjunction with a single-pass resonant acoustic cell. The minimum detection limit of the system for C₂H₄ in air was 0.03 nanoliter per liter. C₂H₄ production of intact Cymbidium (cv Mary Pinchess `Del Rey') flowers was very low (0.015 nanoliter per gram per hour) and showed an increase within 3 hours following emasculation (removal of pollinia plus anthercap). Production peaked (0.14 nanoliter per gram per hour) 8 hours after emasculation and decreased thereafter. Production again increased 45 hours after emasculation. Coloration of the labellum appeared shortly after the first peak; wilting of the petals and sepals appeared during the second rise in ethylene production. The use of the laser photoacoustic technique in plant physiological studies is discussed.