Submitted to: Scientific Horticulture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2008
Publication Date: 6/2/2008
Citation: Charron, C.S., Britz, S.J., Mirecki, R.M., Harrison, D.J., Clevidence, B.A., Novotny, J. 2008. Isotopic labeling of red cabbage anthocyanins with atmospheric 13-CO2. J. Amer. Soc. Hort. Sci. 133(3):351-359. Interpretive Summary: Isotopes are forms of chemical elements found in nature which differ in the number of neutrons in their nuclei. Some isotopes have unstable nuclei that release radiation, while others are completely stable and release no radiation, thus posing no health risk. Because isotopes can be used to tag molecules, isotopic tagging of plants is a powerful strategy for studying metabolic processes. In plant science, isotopic labeling has been used to study carbohydrate biosynthesis, nitrogen metabolism, and photosynthate partitioning. Isotopic labeling of plants consumed as foods has also provided unique opportunities for understanding human nutrient metabolism. We have developed a method to label carbon-based compounds (such as vitamins or flavonoids) in leafy vegetables with a stable (safe) isotope(carbon-13) by cultivation in a controlled enviromnent containing atmospheric carbon-13 dioxide and to identify labeled compounds by high performance liquid chromatography/tandem mass spectrometry. We have chosen red cabbage as our crop for labeling due to our particular interest in anthocyanins and demonstrated success with these red pigments. Therefore, plant scientists, who need to tag plant compounds for research purposes, will use these results.
Technical Abstract: Isotopic labeling of plants provides a unique opportunity for understanding metabolic processes. A significant challenge of isotopic labeling during plant growth is that isotopes must be administered without disrupting plant development and at sufficient levels for mass spectral analysis. We describe a system for isotopic labeling of leafy vegetables with carbon-13 and demonstrate successful incorporation of carbon-13 into anthocyanins of preheading red cabbage (Brassica oleracea L. var. capitata). 'Super Red' red cabbage seedlings were grown for 34 days in an airtight acrylic labeling chamber supplied with carbon-13 dioxide to maintain 400 ppm. Nutrient solution was delivered hydroponically without allowing infusion of natural carbon dioxide into the labeling chamber. Plants were initially grown at 22 degrees C in constant light. Upon canopy closure, anthocyanin development was promoted by reducing nutrient solution concentration and reducing temperature to 10.5 degrees C. Total shoot fresh weight (FW) was 1565 g and root FW was 491 g at harvest. Analysis of red cabbage shoot tissue by high performance liquid chromatography/tandem mass spectrometry (HPLC-MS/MS) indicated the presence of thirty-six anthocyanins, of which eleven are reported here for the first time. Mass shifts representing carbon-13 incorporation into anthocyanins were evident in mass spectra of anthocyanins from labeled tissue and demonstrate successful isotopic labeling.