Imaging Plant Imprints

Indirect desorption electrospray ionization (DESI) mass spectrometry can be used to image the distribution of secondary metabolites in soft plant tissues, such as leaves and petals, Danish scientists report (Anal. Chem., DOI: 10.1021/ac2004967). These small molecules are difficult to image because the waxy outer layer of plants hinders conventional mass spectrometric imaging. Instead of trying to obtain images directly from plant tissue, Christian Janfelt and coworkers at the University of Copenhagen collected mass spectrometric images of various metabolites in plant material imprinted on a porous Teflon surface. In St. John’s wort, for example, they imaged the distribution of hyperforin and hypericin in the plant’s leaves and petals. “The experiment preserves the simplicity of DESI imaging, and the sample preparation is a simple transfer step,” says R. Graham Cooks, a chemistry professor at Purdue University and one of the inventors of DESI. “The fact that leaf material is difficult to image because of the waxy overlayer makes this simple method very attractive.”