Characterization of glucosinolate--myrosinase system in developing salt cress Thellungiella halophila

Glucosinolates are specialized plant metabolites derived from amino acids. They can be hydrolyzed by myrosinases into different degradation products, which have a variety of biological activities. In this study, the compositions and contents of glucosinolates in salt cress (Thellungiella halophila) at different developmental stages were analyzed by high performance liquid chromatography and mass spectrometry (HPLC-MS). Myrosinase activities were also measured. Seven glucosinolates were identified in T. halophila throughout its life cycle. The glucosinolate profiles varied significantly among different tissues. The roots at stage 4 contained the highest concentrations of total, aromatic and indole glucosinolates among all tissues. Whereas roots, flowers and siliques contained all seven glucosinolates, seeds contained only four aliphatic glucosinolates. During development, the concentrations also displayed significant changes. From seeds to cotyledons and from stage 4 roots to stage 5 roots, there were dramatic declines of glucosinolates, which correlated well with changes in myrosinase activities. In other tissues, myrosinase activity alone could not explain the glucosinolate concentration changes. Certain tissues of T. halophila contained Arabidopsis myrosinase TGG1 and TGG2 orthologs. The molecular basis and functional significance of our findings are discussed here.