L-Canavanine: a higher plant insecticidal allelochemical

L-Canavanine, L-2-amino-4-(guanidinooxy)butyric acid, is a potentially toxi c nonprotein amino acid of certain leguminous plants. Many species are prol ific canavanine producers; they divert enormous nitrogen resource to the st orage of this single natural product. Canavanine, a highly effective protec tive allelochemical, provides a formidable chemical barrier to predation an d disease. The accumulated experimental evidence leaves little doubt that the key elem ent in the ability of canavanine to function as an effective protective all elochemical is its subtle structural mimicry of arginine which makes it an effective substrate for amino acid activation and aminoacylation, and its m arked diminution in basicity relative to arginine which mediates the produc tion of structural aberrant, dysfunctional canavanyl proteins. The biological burdens of canavanyl protein formation by canavanine-treated Manduca sexta larvae were carried throughout their remaining life cycle. P rotein-based sequestration of canavanine prevented turnover and clearance o f the free amino acid, and undoubtedly contributed significantly to the ant imetabolic character of this protective allelochemical.