Acetabularia mediterranea and ethylene production in relation with development, circadian rhythm in emission and response to external application

Whole Acetabularia cells evolved ethylene with a decreasing rate in the progression of development, the ultimate stage being cap formation. The algae retained endogenous ethylene in a similar manner. The younger the algae, the higher their capacity to convert exogenously supplied ACC to ethylene. There was a circadian rhythm of ethylene production, peaking in the middle of the light period. Anucleated algae also produced ethylene although at a lower rate, but with the same general circadian pattern. Acetabularia extracts contained ACC and a conjugated form of it, with higher levels at younger stages. Ethephon (10−4 M) had no effect on algal growth but influenced cap formation when applied either continuously (the treatment beginning at defined time points in the 24 h cycle) or in pulses; the efficiency of both types of treatments greatly depended on the circadian time of application.