Systemin

Systemin is a recently discovered plant hormone involved in wound response. It is unique from other plant hormones in that it is a peptide.

Systemin was first identified in tomato leaves. It was found to be an 18-amino acid peptide processed from the C-terminus of a 200-amino acid precursor, which is called prosystemin.

Genes that presumably code for systemins (or prosystemins) also occur in potato, pepper, and black nightshade. But so far, systemin-like hormones have not been identified in species outside the Solanaceae family.