Inhibitors of Ethylene Synthesis and Action: A Comparison of Their Activities in a Lettuce Root Growth Model System

The activity of purported inhibitors of ethylene synthesis and ethylene action was tested in a lettuce ( Lactuca sativa L. ‘Grand Rapids’) root growth model system. Ethylene production by lettuce seedlings was inhibited by three purported inhibitors of ACC-synthase: AOA, l -canaline (CAN), and AVG. However, except for AVG, these compounds did not increase root growth, suggesting that the endogenous basal rate of ethylene production did not play a role in controlling the growth of these seedling roots. The promotive effective of AVG on root growth was not due to an inhibition of ethylene production, since it retained its effect in the presence of externally supplied ethylene. Of the five purported inhibitors of ethylene action studied, only NBA and silver thiosulfate (STS) demonstrated anti-ethylene action without toxic side effects. Three other compounds reported to block ethylene action—CO 2 , DIHB, and MCEB—inhibited growth by themselves and failed to provide clear evidence that they blocked ethylene action in the lettuce root growth assay system. Chemical names used: 1-aminocyclopropane-1-carboxylic acid (ACC); (aminooxy)acetic acid (AOA); [ S -( E )]-2-amino-4-(2-aminoethoxy)-3-butanoic acid (AVG); 2,5-norbornadiene (NBA); 3,5-diiodo-4-hydroxybenzoic acid (DIHB); and 5-methyl-7-chloro-4-ethoxycarbonylmethoxy-2,1,3-benzothiadiazole (MCEB).