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Auxin-induced ethylene production by mung bean (Phaseolus mungo L.) hypocotyl segments was markedly inhibited by 2,4-dinitrophenol regardless of whether or not kinetin was present. Uptake of indoleacetic acid-2-(14)C was also inhibited in the presence of 2,4-dinitrophenol. Segments treated only with indoleacetic acid rapidly converted indoleacetic acid into indole-3-acetylaspartic acid with time whereas kinetin suppressed indoleacetic acid conjugation. Formation of indole-3-acetylaspartic acid was significantly reduced when 2,4-dinitrophenol was present. The suppression of indoleacetic acid conjugation by kinetin and 2,4-dinitrophenol appeared to be additive, and the free indoleacetic acid level in segments treated with 2,4-dinitrophenol in the presence of indoleacetic acid or indoleacetic acid plus kinetin was remarkably higher than in corresponding segments which received no 2,4-dinitrophenol.In the absence of 2,4-dinitrophenol, indoleacetic acid-induced ethylene parallels the free indoleacetic acid level within the tissue. However, in the presence of 2,4-dinitrophenol the rate of ethylene production did not correlate with the free indoleacetic acid level. These results indicate that both indoleacetic acid-induced ethylene production and indoleacetic acid conjugation require a continuous supply of ATP, the formation of which was inhibited by 2,4-dinitrophenol.