Analysis of phytochelatin-cadmium complexes from plant tissue culture using nano-electrospray ionization tandem mass spectrometry and capillary liquid chromatography/electrospray ionization tandem mass spectrometry.

Phytochelatins (PCs, also known as class III metallothioneins), a family of sulfhydryl-rich peptides with the formula (gamma-GluCys)(n)Gly(Pc(n), n = 2-11), are induced in plants, yeast and fungi exposed to heavy metals, and are thought to detoxify metals by forming PC- metal complexes. Although PCs have been detected, PC- metal complexes have not been well characterized. In this work, nano-electrospray ionization tandem mass spectrometry (nano-ESI-MS/MS) and capillary liquid chromatography/electrospray ionization tandem mass spectrometry (capillary LC/ESI-MS/MS) methods were used to analyze PC - Cd complexes isolated from Datura innoxia, also known as Jimsonweed, cell culture exposed to Cd. With nano-ESI-MS/MS and capillary LC/ESI-MS/MS we could simultaneously detect the presence of PCs and PC - Cd complexes from plant cell extracts, unambiguously identify these species and elucidate the nature of individual PC - Cd complexes. Phytochelatins with n = 3-6 were detected, as were PC - Cd complexes with PC(3), PC(4) and PC(5). This is the first study to report the size and nature of native PC - Cd complexes from plant tissue samples. These results demonstrate that the direct analysis of plant extracts using nano-ESI-MS/MS and capillary LC/ESI-MS/MS methods is simple and sensitive to the range of PCs and PC - Cd complexes in plants. Hence these methods open up new opportunities for further quantitative analysis of PCs and PC - metal complexes in cell culture and plant systems to understand the relationship between the biosynthesis of these compounds and metal tolerance.