In this work, a complete cDNA encoding a polygalacturonase (Pd-PG1) has been identified by screening a cDNA library constructed from the ripe mesocarp of Prunus domestica L. subsp. insititia (damson plum). According to similarity in the amino-acid sequence and the absence of pro-sequence, Pd-PG1 belongs to a group of PGs that are expressed in fruit and/or abscission zones. The level of Pd-PG1 mRNA (assessed by real-time semi-quantitative PCR) was stimulated in sepals, petals, and stamens during the flower-opening process. Similarly, the expression of this gene was high during all the pistil-development phases studied, showing a decreasing trend toward flower opening and an increase in senescence. Exogenous ethylene stimulated the PG activity and Pd-PG1 expression in early fruits. In situ hybridization demonstrated that Pd-PG1 expression was higher in teguments, funiculus, endocarp and exocarp, and vascular bundles in ethylene-treated samples. The total PG activity and the presence of Pd-PG1 mRNA were spatially and temporally regulated in fruits. The exocarp has an important contribution to the PG activity and the Pd-PG1 transcription. During maturation and ripening, the levels of Pd-PG1 mRNA were the highest of all those quantified during fruit development. Notably, the seed participation in both gene expression and total PG activity was relevant in all the fruit-development phases studied. The Pd-PG1 transcription was strongly activated during seed maturation and drying. Collectively, these results support the idea that Pd-PG1 is ubiquitously expressed in the reproductive organs of damson plum. A regulation in a tissue-specific manner and the possible participation of other elements of the PG family, tightly coordinated by the developmental programme, should be taken into account.