3 DIFFERENT POLYGALACTURONASES ARE EXPRESSED IN TOMATO LEAF AND FLOWER ABSCISSION, EACH WITH A DIFFERENT TEMPORAL EXPRESSION PATTERN

Abscission, or organ separation, is accompanied by a marked increase i n hydrolases, which are responsible for the degradation of the middle lamella and the loosening of the primary cell wall surrounding cells i n the separation layer. We recently reported on the cloning of a tomat o (Lycopersicon esculentum) polygalacturonase (PG) cDNA, TAPG1, expres sed during leaf and flower abscission. In addition to TAPG1, we have c loned two more PG cDNAs (TAPG2 and TAPG4) that are also expressed duri ng leaf and flower abscission. The peptide sequences for the three abs cission PGs are relatively similar (76-93% identity) yet different fro m the those of tomato fruit PG (38-41% identity). None of the three ab scission PG mRNAs are expressed in fruit, stems, petioles, or anthers of fully open flowers. An RNase protection assay revealed that all thr ee PGs are expressed in leaf and flower abscission zones and in pistil s of fully open flowers. TAPG4 mRNA is detected much earlier than TAPG 1 and TAPG2 mRNA during both leaf and flower abscission.