Ethylene binding in epicotyls of Pisum sativum L. cv. Alaska

Using in-vivo assays at least two classes of ethylene-binding site are shown to exist in pea epicotyls. These classes appear to have identical affinities for ethylene with a KD of 6 · 10(-11)-8 · 10(-11) M; the fast associating class has high and appropriate affinities for physiologically active analogues of ethylene, and CO2 is without effect upon bfinding. Experiments involving suppression of endogenous ethylene production demonstrate that previous work may have underestimated both the amount of binding sites present and the affinity of such sites for ethylene. The apparent inhibition of binding by silver appears to be the consequence of a stimulation of endogenous ethylene production. The possible role of the sites as ethylene receptors is discussed.