“Afterlife Experiment” : Use of MALDI-MS and SIMS Imaging for the Study of the Nitrogen Cycle within Plants

As part of a project to demonstrate the science of decay, a series of mass spectrometry imaging experiments were performed. The aim was to demonstrate that decay and decomposition are only part of the story and to show pictorially that atoms and molecules from dead plants and animals are incorporated into new life. Radish plants (Raphanus sativus) were grown hydroponically using a nutrient system containing ¹⁵N KNO₃ (98% labeled) as the only source of nitrogen. Plants were cropped and left to ferment in water for 2 weeks to create a radish “tea”, which was used as a source of nitrogen for radish grown in a second hydroponics experiment. After 5 weeks of growth, the radish plants were harvested and cryosectioned, and sections were imaged by positive-ion MALDI and SIMS mass spectrometry imaging. The presence of labeled species in the plants grown using ¹⁵N KNO₃ as nutrient and those grown from the radish “tea” was readily discernible. The uptake of 15N into a number of identifiable metabolites has been studied by MALDI-MS and SIMS imaging.