| Petal abscission in Pelargonium xhortorum occurs in response to pollination. Pollination of florets at the pollination receptive stage induces an increase in ethylene production by the pistil which precedes petal abscission. The purpose of this study was to define the regulation of post-pollination ethylene production and its role in petal abscission. The experiments focused on the effect of pollination on the levels of 1-aminocyclopropane-1-carboxylic acid (ACC), malonyl-ACC (MACC), ACC synthase transcripts, and the activity of ACC synthase and ACC oxidase in floral tissues. Furthermore, the effects of inhibitors of ACC synthase activity (aminoethoxyvinylglycine) and of protein synthesis (cycloheximide), were evaluated on post-pollination responses. The elevated ethylene production in the stigma+style after pollination was accompanied by increased ACC and MACC levels. The latter was the result of increased ACC synthase in these tissues. Nevertheless, in the basal part of the petals of pollinated flowers, ACC levels and ACC synthase activity were increased but not ACC oxidase activity. These results suggest that there is a post-translational control of ACC synthase activity in pollinated geranium flowers.;To study the role of cellulases in petal abscission, the expression of three cellulase genes, PCX10, PCX59 and PCX102, was examined after pollination or ethylene treatment. Pollination decreased the mRNA levels of these two genes initially, but they increased at 2 hours after pollination. Exogenous ethylene slightly increased the levels of PCX59 and PCX102 in pistils. Ethylene decreased the mRNA levels of PCX102 in the upper pistil of abscising flowers. In nonabscising flowers, expression of PCX59 and PCX102 was detected in the upper pistil while only PCX102 mRNA was detected in the lower pistil, including the petal abscission zone and in the upper part of petal. The expression of PCX102 in the tissues of the abscission zone may be associated with its possible involvement in the abscission of petals. |
