title: ToF-SIMS imaging of capsaicinoids in Scotch Bonnet peppers (Capsicum chinense).
abstract: Peppers (Capsicum spp.) are well known for their ability to cause an intense burning sensation when eaten. This organoleptic response is triggered by capsaicin and its analogs, collectively called capsaicinoids. In addition to the global popularity of peppers as a spice, there is a growing interest in the use of capsaicinoids to treat a variety of human ailments, including arthritis, chronic pain, digestive problems, and cancer. The cellular localization of capsaicinoid biosynthesis and accumulation has previously been studied by fluorescence microscopy and electron microscopy, both of which require immunostaining. In this work, ToF-SIMS has been used to image the distribution of capsaicinoids in the interlocular septum and placenta of Capsicum chinense (Scotch Bonnet peppers). A unique cryo-ToF-SIMS instrument has been used to prepare and analyze the samples with minimal sample preparation. Samples were frozen in liquid propane, cryosectioned in vacuum, and analyzed without exposure to ambient pressure. ToF-SIMS imaging was performed at -110 °C using a Bi3 (+) primary ion beam. Molecular ions for capsaicin and four other capsaicinoids were identified in both the positive and negative ToF-SIMS spectra. The capsaicinoids were observed concentrated in pockets between the outer walls of the palisade cells and the cuticle of the septum, as well as in the intercellular spaces in both the placenta and interlocular septum. This is the first report of label-free direct imaging of capsaicinoids at the cellular level in Capsicum spp. These images were obtained without the need for labeling or elaborate sample preparation. The study demonstrates the usefulness of ToF-SIMS imaging for studying the distribution of important metabolites in plant tissues.
authors.affiliation: Physikalisches Institut, Universität Münster, 48149 Münster, Germany and Department of Chemical Engineering, The University of the West Indies, St. Augustine, Trinidad and Tobago.
authors.forename: Bonnie J
authors.initials: BJ
authors.lastname: Tyler
authors.affiliation: Physikalisches Institut, Universität Münster, 48149 Münster, Germany.
authors.forename: Richard E
authors.initials: RE
authors.lastname: Peterson
authors.affiliation: Department of Chemical Engineering, The University of the West Indies, St. Augustine, Trinidad and Tobago.
authors.forename: Therese G
authors.initials: TG
authors.lastname: Lee
authors.affiliation: Physikalisches Institut, Universität Münster, 48149 Münster, Germany.
authors.forename: Felix
authors.initials: F
authors.lastname: Draude
authors.affiliation: Physikalisches Institut, Universität Münster, 48149 Münster, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Pelster
authors.affiliation: Physikalisches Institut, Universität Münster, 48149 Münster, Germany.
authors.forename: Heinrich F
authors.initials: HF
authors.lastname: Arlinghaus
mesh_terms: D002211:Capsaicin / Q000031:analogs & derivatives* / Q000032:analysis*; D002212:Capsicum / Q000737:chemistry*; D006801:Humans; D061848:Optical Imaging / Q000379:methods*; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods*
chemical_list: D002211:Capsaicin