Polygalacturonase (PG, EC 3.2.1.15) is one of the cell wall hydrolases involved in the cell separation processes which occur during ripening of some fleshy fruits (FISHER and BENNETT 1991), as well as during abscission of leaves and fruits (HUBERMANN and GOREN 1979; RASC~O et al. 1985; TAYLOR et al. 1990; BONGHI et al. 1992; TAYLOR et al. 1993). In particular, endopolygalacturonase of tomato fruit is the most widely known form of this enzyme, having been characterized at molecular and biochemical level (see literature in ZHENG et al. 1992). Endopolygalacturonase activity has also been found in peach during both abscission and development of fruits, while no such activity could be detected during leaf abscission (BONGHI et al. 1992; ZANCHIN et al. 1993). A few years ago it was observed that polyclonal antibodies raised against a tomato fruit PG (i.e., PGZA) recognized, in soft ripe fruits of peach, a polypeptide with molecular mass similar to that of PG2A. Furthermore, using as a probe a cDNA coding for tomato fruit endopolygalacturonase, the same researchers were able to clone and characterize a 3.5 kb fragment of peach genomic DNA (LEE et al. 1990). On the basis of sequence analysis it was concluded that, besides an unidentified sequence, it contained about the 3' half of a gene which showed, in the coding regions, extensive homology with the tomato PG gene. According to the same researchers, such homology could explain the observed cross-reaction between the antibody to tomato fruit PG and a peach polypeptide, which was therefore suggested to be a peach endopolygalacturonase and the product of the partly characterized gene (LEE et al. 1990). In tomato the gene encoding the fruit endopolygalacturonase seems to be expressed during the fruit ripening, but not during the leaf abscission. In fact, despite a significative rise in PG activity, an antibody to fruit PG did not recognize any leaf abscission protein. Moreover, a cDNA encoding a tomato fruit PG gave no hybridization to mRNA obtained from activated abscission zones of tomato leaves (TAYLOR et al. 1990). In peach it has recently been shown that a cDNA coding for tomato fruit PG hybridized to mRNA obtained from fruit abscission zones but not from leaf ones where, in any case, no PG activity had been detected (BONGHI et al. 1992). In peach, cell separation events which show an involvement of endopolygalacturonase, are not restricted to fruit softening and abscission. Recently, it has been found that PG activity can also be detected throughout the fruit growth ( ZANCHIN et al. in press). On the basis of the above findings we considered it of some interest to see whether the endopolygalacturonase activity, observed in the course of different cell separation events in peach, is due to expression of the partly known PG gene (LEE et al. 1990) or, as already observed in tomato (TAYLOR et al. 1990), only some of that activity can be ascribed to expression of that gene
