EXPRESSION OF ETHYLENE BIOSYNTHETIC-PATHWAY MESSENGER-RNAS IS SPATIALLY REGULATED WITHIN CARNATION FLOWER PETALS

The spatial regulation of ethylene biosynthesis within carnation (Dianthus caryophyllus L. cv. White Sim) flower petals was investigated. When detached petals separated into upper and basal portions were exposed to ethylene, autocatalytic ethylene production specifically in the basal portions resulted. Ethylene-induced ethylene production in the basal petal tissue was associated with the accumulation of mRNAs for 1-aminocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase. In contrast, the upper petal portions did not accumulate ACC synthase mRNA nor exhibit an induction of ACC synthase activity in response to ethylene. Upper petal tissue exhibited a transient accumulation of ACC oxidase mRNA and increased ACC oxidase activity in response to ethylene, although the levels of both were significantly lower than that exhibited by basal tissue. Both upper and basal petal tissue responded to ethylene with the accumulation of senescence-related mRNAs represented by the cDNA clones pSR5 and pSR12, indicating that the lack of expression of ACC synthase and the limited accumulation of ACC oxidase mRNA were not a result of overall differences in ethylene responsiveness between upper and basal petal tissue. Upper portions isolated from intact senescing petals produced elevated levels of ethylene at approximately 25 % the rate of basal tissue and contained lower, but detectable levels of ACC synthase and ACC oxidase mRNAs as compared to basal petal tissue. Following dissection, the upper petal tissue exhibited a decrease in ethylene production, while the basal tissue continued to produce ethylene at elevated rates. These results indicate ethylene production in the upper tissue is largely the result of transport of ACC and ethylene from the basal tissue.