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

The spatial regulation of ethylene biosynthesis within carnation (Dian thus caryophyllus L. cv. White Sim) flower petals was investigated. Wh en detached petals separated into upper and basal portions were expose d to ethylene, autocatalytic ethylene production specifically in the b asal portions resulted. Ethylene-induced ethylene production in the ba sal petal tissue was associated with the accumulation of mRNAs for 1-a minocyclopropane-1-carboxylate (ACC) synthase and ACC oxidase. In cont rast, the upper petal portions did not accumulate ACC synthase mRNA no r exhibit an induction of ACC synthase activity in response to ethylen e. Upper petal tissue exhibited a transient accumulation of ACC oxidas e mRNA and increased ACC oxidase activity in response to ethylene, alt hough the levels of both were significantly lower than that exhibited by basal tissue. Both upper and basal petal tissue responded to ethyle ne with the accumulation of senescence-related mRNAs represented by th e cDNA clones pSR5 and pSR12, indicating that the lack of expression o f ACC synthase and the limited accumulation of ACC oxidase mRNA were n ot a result of overall differences in ethylene responsiveness between upper and basal petal tissue. Upper portions isolated from intact sene scing 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 tissu e. Following dissection, the upper petal tissue exhibited a decrease i n ethylene production, while the basal tissue continued to produce eth ylene at elevated rates. These results indicate ethylene production in the upper tissue is largely the result of transport of ACC and ethyle ne from the basal tissue.