Potentiating Effect of Pure Oxygen on the Enhancement of Respiration by Ethylene in Plant Storage Organs: A Comparative Study

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Abstract
Fruits and bulky storage organs [Solanum tuberosum cv. Russet, Persea americana cv. Hass, Musa covendishii cv. Valery, Ipomoea batatas, Pastinacea sativa, Daucus carota, Brassica napus, B. rapa, Helianthus tuberosus, Beta vulgaris, Pachyrhizus erosus, Rhaphanus sativus, Armoracia rusticana and Kigelia pinnata] were studied with respect to the effect of pure O2 on the extent and time-course of the respiratory rise induced by ethylene. In 1 group, of which potato (S. tuberosum cv. Russet) and carrot (D. carota) are examples, the response to ethylene in O2 is much greater than in air. In a 2nd group, of which avocado (P. americana Mill. cv. Hass) and banana (M. cavendishii Lambert cv. Valery) are examples, air and O2 are usually effective. When O2-responsive organs are peeled, air and O2 synergize the ethylene response to the same extent in parsnip (P. sativa), whereas O2 is more stimulatory than air in carrots. In the latter instance, carrot flesh apparently contributes significantly to diffusion resistance. The release of CO2, an ethylene antagonist, is recognized as another element in the response to peeling. The potentiating effect of O2 is considered to be primarily on ethylene action in the development of the respiratory rise rather than on the respiration process per se. On the assumption that diffusion controls O2 movement into bulky organs and the peel represents the major diffusion barrier, simple calculations indicate that the O2 concentration in untreated organs in air readily sustains respiration. In ethylene-treated organs in pure O2, the internal O2 concentration is more than enough to maintain the high respiration rates. Skin conductivity to O2 is the fundamental parameter differentiating O2-responsive from O2-nonresponsive fruits and bulky storage organs. The magnitude of the ethylene-induced respiratory rise is controlled by permeability characteristics of the peel.