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Ethylene controls multiple physiological processes in plants, including cell elongation. Consequently, ethylene synthesis is regulated by internal and external signals. We show that a light-entrained circadian clock regulates ethylene release from unstressed, wild-type Arabidopsis (Arabidopsis thaliana) seedlings, with a peak in the mid-subjective day. The circadian clock drives the expression of multiple ACC SYNTHASE genes, resulting in peak RNA levels at the phase of maximal ethylene synthesis. Ethylene production levels are tightly correlated with ACC SYNTHASE 8 steady-state transcript levels. The expression of this gene is controlled by light, by the circadian clock, and by negative feedback regulation through ethylene signaling. In addition, ethylene production is controlled by the TIMING OF CAB EXPRESSION 1 and CIRCADIAN CLOCK ASSOCIATED 1 genes, which are critical for all circadian rhythms yet tested in Arabidopsis. Mutation of ethylene signaling pathways did not alter the phase or period of circadian rhythms. Mutants with altered ethylene production or signaling also retained normal rhythmicity of leaf movement. We conclude that circadian rhythms of ethylene production are not critical for rhythmic growth.

The ethylene production rate of cut sweet pea flower buds increased 37-fold during the first 48 h of their vase life. This increase in ethylene production was accompanied by petal wilting at 72 h and abscission of the buds 24 h later. Exposure of the cut spikes to the ethylene action inhibitor diazocyclopentadiene (DACP, 170 μI 1 -1) for 18 h under fluorescent lights delayed subsequent wilting and abscission and promoted bud opening. Silver thiosulphate (0·2 mM) was more effective than DACP, delaying wilting for longer and preventing abscission entirely.