Ethylene Modification of an Auxin Pulse in Cotton Stem Sections

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Abstract
The effect of ethylene on the basipetal movement of indole-3-acetic acid-1-(14)C through cotton stem sections (Gossypium hirsutum, L. var. Stoneville 213) was studied apart from processes involved in the uptake and exit of auxin by the section. Stem sections 60 mm in length were pretreated with ethylene or placed in room air (control) and pulse labeled for 20 min with IAA-1-(14)C. In both the ethylene treated and control sections, the IAA-1-(14)C taken up moved basipetally as a peak of radioactivity. Generally, the applied pulse moved down the stem sections at an average velocity of approximately 5.8 mm per hr. In some experiments, however, ethylene slightly reduced the velocity of auxin transport. Although the peak of radioactivity became broader and more dispersed during its migration through the section, it was still distinguishable after 7 hr of transport.As the ethylene pretreatment periods were increased from 1.5 to 3.0 hr there was a progressively greater loss of activity from the pulse of applied IAA-1-(14)C during its basipetal movement. On the average, 4% more activity was lost from the applied pulse at 1.5 hr, 15% more at 2.0 hr and 26% more at 3.0 hr when compared to control stem sections.The data establish that ethylene inhibits auxin transport in vivo, and it is proposed that the effect is due possibly to increased rates of auxin immobilization.