EFFECT OF POLLINATION ON ACCUMULATION OF ACC SYNTHASE AND ACC OXIDASETRANSCRIPTS, ETHYLENE PRODUCTION AND FLOWER PETAL ABSCISSION IN GERANIUM (PELARGONIUM-X-HORTORUM BAILEY,L.H.)

Self-pollination of diploid zonal geranium (Pelargonium x hortorum L.H . Bailey) florets leads to a dramatic rise in ethylene production. fol lowed by abscission within 4 h. Neither wounding of the stigma, pollin ation with tetraploid pollen, nor heat-killed self pollen could elicit as much ethylene production and petal abscission as self-pollination. A cDNA sharing sequence identity with ACC synthase (GACS2) and three different cDNAs sharing sequence identity with ACC oxidase (GACO1, GAC O2, GACO3) were isolated from geranium pistils. Transcripts hybridizin g with these probes increased slightly in response to self-pollination , but the degree of accumulation in response to various treatments did not correlate with ethylene production. When calculated on a per-plan t-part basis, transcripts hybridizing with GACS2 were equally distribu ted among the stigma+style, sterile ovary, and ovary tissues, but tran scripts hybridizing with the three ACC oxidase clones were differentia lly distributed. All transcripts were differentially expressed among t he other tissues of the plant, with GACO1 being the most widely distri buted. Ethylene production in geranium pistils was not autocatalytic. Propylene failed to induce ethylene production and ethylene did not in duce the accumulation of ACC synthase or ACC oxidase transcripts. ACC accumulated in the stigma and style, and to a smaller extent in the st erile ovary, after pollination. These data support a model of pollinat ion-induced ethylene production by post-transcriptional regulation of ethylene biosynthetic gene expression.