Role of Ethylene in Fruit Ripening

Abstract

There have arisen two schools of thought concern- ing the role of ethylene in fruit maturation: the classic view of Kidd and West (26) and Hansen (22) that ethylene is a ripening hormone, and a recent interpre- tation by Biale et al. (7, 3, 4) that it is a by-product of the ripening process.The original presentation of the by-product theory in this journal (7) was temper- ed with the reminder that 0.1 ppm ethylene may stimulate ripening, so that "in the absence of any information correlating the internal ethylene content with the rate of ethylene production, one can advance the argument that small quantities sufficient to in- duce ripening are produced prior to the rise of respiration, but measurable amounts are detected only after the onset of the climacteric."The development of highly sensitive gas chromatographic instruments makes it feasible to appraise critically those instances in whiclh fruits have been reported to produce ethylene not at all or only after the climacteric has started, and also to determine the content of ethylene witllin a fruit at the onset of the rise in respiration.Results of such experiments are reported in this communica- tion, and they have a direct bearing on the problem of whetlher or not ethylene is a natural ripening hor- mone. Materials.Mangoes (Magiiifera indica L., cv.Kent & Haden) were harvested in local orchards.The fruits used for each experiment were picked from the same tree on the same day and were all of about equal size and apparent maturity.Bananas (Miusa acuiiniata cv.Gros Mfichel) harvested at 34 fullness were ship- ped from Ecuador.Pineapples [Ananas comnosus (L.) AMerr.] at various stages of maturity were flown from Honduras; they arrived in very satisfactory condition w%ithin a day of picking.The Citrus Ex- periment Station at Tampa, Fla. provided oranges [Citrl(s sinensis (L.) Osbeck] and passion fruits (Passiflora eddlis,Sims); other fruits were purchased in local markets.'