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

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Abstract
Phytochelatins (PCs, also known as class III metallothioneins), a family of sulfhydryl‐rich peptides with the formula (γ‐GluCys)nGly(Pcn, 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 PC3, PC4 and PC5. 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. Copyright © 1999 John Wiley & Sons, Ltd.