POLYGALACTURONASE EXPRESSION DURING LEAF ABSCISSION OF NORMAL AND TRANSGENIC TOMATO PLANTS

Polygalacturonase (PG, EC 3.2.1.15), an enzyme commonly found in ripening fruit, has also been shown to be associated with abscission. A zone-specific rise in PG activity accompanies the abscission of both leaves and flowers of tomato (Lycopersicon esculentum Mill.) plants. Studies of transgenic plants expressing an antisense RNA for fruit PG indicate that although the enzyme activity in transgenic fruit is < 1% of that in untransformed fruit, the PG activity in the leaf abscission zone increases during separation to a similar value to that in untransformed plants. The timing and rate of leaf abscission in transgenic plants are unaffected by the introduction of the antisense gene. A polyclonal antibody raised against tomato fruit PG does not recognise the leaf abscission protein. Furthermore a complementary DNA (cDNA) clone (pTOM6), which has been demonstrated to code for fruit PG, does not hybridise to mRNA isolated from the abscission-zone region of tomato leaves. These results indicate that the PG protein in abscission zones of tomato is different from that in the fruit, and that the gene coding for this protein may also be different.