| In this study, the relationship of pollination, ethylene, and flower petal abscission of zonal geranium (Pelargonium Xhortorum L. H. Bailey) was examined. In order to isolate and characterize ethylene-responsive geranium pistil genes, a cDNA library was constructed from poly (A+) mRNA isolated from ethylene-treated geranium pistils and screened using two approaches. Differential screening of the library with cDNA probes synthesized from ethylene-treated and untreated mRNAs led to the isolation of two putative cDNA clones which encode glycine-rich RNA binding proteins. Further experiments revealed that transcripts for these genes are regulated by an endogenous circadian rhythm, but not by ethylene or pollination. Subsequently, it was concluded that these genes have no involvement in petal abscission in response to pollination or exogenous ethylene.;Screening of the cDNA library with heterologous probes encoding ACC synthase and ACC oxidase isolated from carnation flower petals led to the isolation of putative cDNA clones encoding the geranium versions of these enzymes. Further experiments revealed that transcripts for these clones are transcriptionally regulated by self pollination, but not by exogenous ethylene. Accumulation of mRNAs for ACC synthase and ACC oxidase corresponded to an increase in pollination-induced ethylene production and subsequent petal abscission. After pollination, ACC accumulates specifically in the stigma, suggesting that induction of ACC synthase and ethylene production is specific to the stigma. Pollen tube germination and growth in the stigma may be required for pollination-induced ethylene production and petal abscission. This initial physiological and molecular characterization of the flower petal abscission response, combined with future studies pertaining specifically to the petal abscission zone, will allow for the elucidation of the signal transduction pathway involved in the flower petal abscission response. With this knowledge, better methods can be developed to alleviate the problems associated with abscission of many important horticultural commodities. |
