Effects of Ethylene on Potato Tuber Respiration

Abstract

Treatment of potato tubers (Solanum tuberosum L.) with ethylene gas causes a rapid rise in their respiration rate, reaching 5 to 10 times the rate of untreated tubers over 30 hours of treatment and then falling slowly. The response shows a lag of 8 hours, and more than 24 hours of exposure is required for maximum effect; the temperature optimum is near 25 C. In sensitivity to low concentrations and dependence on temperature, the phenomenon is similar to the effect of ethylene on the respiration of climacteric and nonclimacteric fruits. Treated potato tubers returned to air recover their sensitivity to ethylene more slowly than do nonclimacteric fruits (e.g., mature green oranges). It is proposed that the respiratory rise characteristic of ripening in climacteric fruits and of the wound response in plant tissues is induced by a rise in endogenous tissue ethylene.Ethylene is a plant hormone having diverse effects on a wide range of plant tissues. In spite of its apparent importance as a regulator of plant growth, the site and mechanisms of its actions have not yet been elucidated (10, 12). We recently described the remarkable effect of this substance on the respiration of intact potato tubers (14) and suggested the possible value of the phenomenon as a simple system for the study of the mode of action of ethylene. We report here a more detailed study of the respiratory response of potato tubers to ethylene gas and discuss the mechanisms that may be involved. MATERIALS AND METHODSMature (100 day) potato tubers (Solanum tuberosum L., cv. White Rose) were dug from the field, washed, and stored at 20 C until needed; all experiments except the temperature trial were conducted at this temperature. Commercially obtained tubers were found to be unsatisfactory because previous cold storage and careless handling may have had pronounced effects on their physiology. Mature green sweet oranges (Citrus sinensis Osbeck, seedling) were obtained from a local garden.Respiration measurements were made by placing individual specimens in 500-ml jars ventilated with a stream of air flowing at about 1.5 liter per hr and measuring the CO, content of the effluent air by gas chromatography. Ethylene was in-'This work was supported in part by research grant FD-00071 from the United States Public Health Service.2 On leave from Plant Diseases Division, D.S.I.R., Auckland, New Zealand. troduced into gas streams from a pressure cylinder through a reduction valve and appropriate capillary flowmeters, and the final concentration was verified with a gas chromatograph.When it was necessary to measure respiration in a static system, individual specimens were placed in 9-liter jars, and ethylene in appropriate amounts was added through a rubber septum. Samples of the jar atmosphere were taken through the septum for determination of the CO2 content. Changes in concentration resulting from sample removal were insignificant, and the jar volume was such that the concentration of CO2 seldom rose above 0.5%. RESULTS Effect of Ethylene Treatment on ...

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