Proteinase inhibitor gene families: strategies for transformation to improve plant defenses against herbivores. 
Recent evidence indicates that the presence of serine proteinase inhibitors in plant leaves can reduce predation by insects.  Plants can now be transformed with proteinase inhibitor genes with strong promoters to express the inhibitor proteins in relatively high levels at specific times.  Inhibitors having variable specificities against digestive proteinases of insects and pathogens can now be assessed for their possible role(s) in natural plant defense and for their potential usefulness in protecting crop plants against herbivores.