Ethylene Binding Receptors — Is There More Than One?

Abstract

In the late 1970s, ethylene binding was reported in tobacco leaves [13, 20]. About the same time a report on compartmentation of ethylene in Phaseolus vulgarus cotyledons appeared [10]. Here, too, ethylene appears to be binding. Since then binding has been reported in a large number of plant tissues, and a report has appeared on non-physiological binding [1]. The usual parameters of binding have been determined in attempts to relate ethylene binding with physiological activity. Various criteria have been made for considering an isolated receptor as physiologically important. Trewavas and Jones [24] have presented the following: (1) it should show reversible, specific and saturable binding; (2) its binding dissociation constants should be at or lower than the biologically active concentrations; (3) the number of binding sites should be small; and (4) chemical modification of substrates should lead to equivalent modification in binding affinity and biological activity. For the most part, the data collected to date meet these criteria, and much of the data would suggest a single binding site. Ethylene is the only plant hormone for which binding can be measured in vivo, which adds another dimension to studies by allowing another parameter (diffusion from the site) to be measured.