Role of glucosinolates in insect-plant relationships and multitrophic interactions

Glucosinolates present classical examples of plant compounds affecting insect-plant interactions. They are found mainly in the family Brassicaceae, which includes several important crops. More than 120 different glucosinolates are known. The enzyme myrosinase, which is stored in specialized plant cells, converts glucosinolates to the toxic isothiocyanates. Insect herbivores may reduce the toxicity of glucosinolates and their products by excretion, detoxification, or behavioral adaptations. Glucosinolates also affect higher trophic levels, via reduced host or prey quality or because specialist herbivores may sequester glucosinolates for their own defense. There is substantial quantitative and qualitative variation between plant genotypes, tissues, and ontogenetic stages, which poses specific challenges to insect herbivores. Even though glucosinolates are constitutive defenses, their levels are influenced by abiotic and biotic factors including insect damage. Plant breeders may use knowledge on glucosinolates to increase insect resistance in Brassica crops. State-of-the-art techniques, such as mutant analysis and metabolomics, are necessary to identify the exact role of glucosinolates. Acronyms and Definitions Constitutive defense: defense characteristics that are always expressed in the plant Induced defense: induced responses that reduce the negative fitness consequences of an attack by a pest or pathogen Induced response: change in chemical compound levels after damage by herbivores Multitrophic interactions: interactions that involve more than two trophic levels in a food web Sequestration: the active accumulation of material as a means of protection against organisms from a higher trophic level Synomone: an allelochemical that elicits a response from which both the originator and receiver benefit Token (or sign) stimulus: a stimulus by which an animal distinguishes an important object