This invention seeks to provide means by which transgenic plants harbour within their genome a chimaeric gene which when expressed produces a protein having a cytotoxic effect. Cytotoxicity is achieved by way of a protein or part thereof capable of blocking cellular protein synthesis, such as a maize ribosome inactivating protein or part thereof. The chimaeric gene may comprise a promoter operably linked to a sequence encoding a protein capable of blocking cellular protein synthesis such that the promoter is inducible at and/or adjacent to a target site.