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Production and Action of Ethylene in Senescing Leaf Discs

Effect of Indoleacetic Acid, Kinetin, Silver Ion, and Carbon Dioxide ¹

^a Post Harvest Plant Physiology Laboratory, Beltsville Agricultural Research Center, United States Department of Agriculture, Beltsville, Maryland 20705

Supraoptimal concentrations of indoleacetic acid (IAA) stimulated ethylene production, which in turn appeared to oppose the senescence-retarding effect of IAA in tobacco leaf discs. Kinetin acted synergistically with IAA in stimulating ethylene production, but it inhibited senescence. Silver ion and CO₂, which are believed to block ethylene binding to its receptor sites, delayed senescence in terms of chlorophyll loss and stimulated ethylene production. Both effects of Ag⁺ were considerably greater than those of CO₂. IAA, kinetin, CO₂, and Ag⁺, combined, acted to increase ethylene production further. Although this combination increased ethylene production about 160-fold over that of the control, it inhibited senescence. Treatment with 25 µl/l of ethylene in the presence of IAA enhanced chlorophyll loss in leaf discs and inhibited by about 90% the conversion of L-[3,4-¹⁴C] methionine to ¹⁴C₂H₄ suggesting autoinhibition of ethylene production.

The results suggest that ethylene biosynthesis in leaves is controlled by hormones, especially auxin, and possibly the rate of ethylene production depends, via a feedback control system, on the rates of ethylene binding at its receptor sites.

¹ This work was supported by the United States Department of Agriculture, Science and Education Administration, Agricultural Research, and the University of Maryland in Cooperative Agreement No. 12-14-1001-1201.

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