Localization of flavonoids in seeds by cluster time-of-flight secondary ion mass spectrometry imaging

Time-of-flight secondary ion mass spectrometry imaging has been used to map flavonoids in fresh seed sections of peas (Pisum sativum) and Arabidopsis thaliana. While for peas a very simple preparation method derived from mammalian tissue imaging could be utilized, several preparation methods had to be tested for the A. thaliana seeds before obtaining tissue sections on which the diagnostic ions were not delocalized. For such small and stiff biological material, none of the methods currently used in histology or scanning electron microscopy could be transferred to mass spectrometry imaging. Only the embedding of the fresh seeds in a polyester resin, followed by the analysis of the block after having obtained a flat surface section with a diamond blade, gave sensitive and reproducible results. Several flavonoid ions have been detected in the sections, showing increased concentrations of flavonoids in the seed coats. The method was finally applied to confirm the variations in the flavonoid content of seeds from different A. thaliana mutants.