Factors regulating ethylene biosynthesis in etiolated Arabidopsis thaliana seedlings

while the other interactions tested were essentially additive. We examined the effect on etiolated Arabidopsis thaliana seedlings of a wide variety of factors that are known to induce Auxin and cytokinin have been shown to act synergistically to elevate ethylene biosynthesis in many other plant tissues. We ethylene in other plant tissues. Auxin, cytokinin, brassinosteroid and cupric ion were found to highly elevate ethylene show that the synergism between cytokinin and auxin in production in these seedlings, but several other signaling comArabidopsis is due to an enhancement of the effects of auxin, pounds, as well as wounding and mechanical stimulation, had but not by increased elevation of ACS4 mRNA levels. These little or no effect. A mutant that disrupts the ACS5 gene results suggest that cytokinin acts post-transcriptionally to (cin5) was partially defective in the induction of ethylene in increase ACS4 function, which, coupled with the observation that auxin elevates ACS4 mRNA levels, accounts for the the presence of brassinosteroids, suggesting a role for this synergistic interaction. isoform in mediating this response. Cytokinin displayed a synergistic interaction with both brassinosteroid and auxin,