LEAVES OF TRANSGENIC TOMATO PLANTS OVEREXPRESSING PROSYSTEMIN ACCUMULATE HIGH-LEVELS OF CYSTATIN

A systemin-inducible cystatin (cysteine proteinase inhibitor) from tom ato (Lycopersicon esculentum) leaves was isolated to homogeneity by a combination of differential precipitation with (NH4)(2)SO4 and affinit y chromatography using immobilized papain. SDS-PAGE analyses revealed that the inhibitor had a M-r of about 87 kDa. Partial amino acid seque nce from CNBr fragments of the purified protein showed a high degree o f homology with various plant cystatins. The tomato cystatin strongly inhibited papain, with a K-l of 4.7 nM. Antibodies raised against cowp ea cystatin cross-reacted with tomato cystatin, in Western blot analys es, indicating that the inhibitors from cowpea and tomato leaves are c losely related. The inducibility of this protease inhibitor suggests t hat it has an important role for plant defense against herbivore preda tors. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.