Benzoxazinoids: Reactivity and Modes of Action of a Versatile Class of Plant Chemical Defenses

In order to protect themselves from biotic stresses, including enemies and competitors, many plants recruit defensive secondary metabolites. Compounds containing a 2-hydroxy-2H-1,4benzoxazin-3(4H)-one skeleton and their derivatives, collectively known as benzoxazinoids, are common secondary metabolites in many grasses, including important cereal crops such as maize, wheat, and rye, as well as several dicot species. This diverse class of compounds is known for its broad range of antifeedant, insecticidal, antimicrobial, and allelopathic activities. However, the mechanisms underlying such biological activities are not yet completely understood. The present review aims to summarize the current knowledge on the chemical reactivity of benzoxazinoids in biological systems and associate it to their proposed modes of action. Structure-activity relationships for a wide spectrum of biological effects are critically discussed and directions for future research are addressed.