Role of oxygen in auxin-induced ethylene production

Ethylene production by IAA-treated mung bean hypocotyl segments under various oxygen levels in the ambient atmosphere was examined. Rate of ethylene production was dependent upon oxygen levels, and gave a sigmoidal curve against oxygen levels. Tissue segments preincubated with IAA in low oxygen levels (1–10% O2 in N2) produced ethylene without a lag period at a rate higher than that by control tissue segments preincubated in air, when they were exposed to a high oxygen level (air, 21% O2). The effect of cycloheximide on tissue segments transferred from a low oxygen level to air was not much different from that on ethylene production by control tissue segments previously incubated in air. Incorporation of U-14C-leucine into the protein fraction by tissue segments placed in nitrogen was negligible, but that in 2% oxygen was 10 to 14% of that in air. It was concluded that oxygen was an essential factor for both the induction process of the ethylene producing system and the synthesis of ethylene, and that although synthesis of ethylene is dependent upon oxygen levels, formation of the ethylene producing system proceeded even under low oxygen levels.