title: Selenoglucosinolates and their metabolites produced in Brassica spp. fertilised with sodium selenate.
abstract: Glucosinolates are sulphur-containing glycosides found in many Brassica spp. that are important because their aglycone hydrolysis products protect the plant from herbivores and exhibit anti-cancer properties in humans. Recently, synthetically produced selenium analogues have been shown to be more effective at suppressing cancers than their sulphur counterparts. Although selenium is incorporated into a number of Brassica amino acids and peptides, firm evidence has yet to be presented for the presence of selenium in the glucosinolates and their aglycones in planta. In this study broccoli and cauliflower florets, and roots of forage rape, all obtained from plants treated with sodium selenate, were analysed for the presence of organoselenides. GC-MS analysis of pentane/ether extracts identified six organoselenium compounds including selenium analogues of known myrosinase-derived Brassica volatiles: 4-(methylseleno)butanenitrile, 5-(methylseleno)pentanenitrile, 3-(methylseleno)propylisothiocyanate, 4-(methylseleno)butylisothiocyanate, and 5-(methylseleno)pentylisothiocyanate. LC-MS analysis of ethanolic extracts identified three selenoglucosinolates: 3-(methylseleno)propylglucosinolate (glucoselenoiberverin), 4-(methylseleno)butylglucosinolate (glucoselenoerucin), and 5-(methylseleno)pentylglucosinolate (glucoselenoberteroin). LC-MS/MS analysis was used to locate the position of the selenium atom in the selenoglucosinolate and indicates preferential incorporation of selenium via selenomethionine into the methylselenyl moiety rather than into the sulphate or β-thioglucose groups. In forage rape, selenoglucosinolates and their aglycones (mainly isothiocyanates), occurred at concentrations up to 10% and 70%, respectively, of their sulphur analogues. In broccoli, concentrations of the selenoglucosinolates and their aglycones (mainly nitriles) were up to 60% and 1300%, respectively of their sulphur analogues. These findings indicate the potential for the incorporation of high levels of selenium into Brassica glucosinolates.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited (Plant & Food Research), Private Bag 11600, Palmerston North 4442, New Zealand. adam.matich@plantandfood.co.nz
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Matich
authors.forename: Marian J
authors.initials: MJ
authors.lastname: McKenzie
authors.forename: Ross E
authors.initials: RE
authors.lastname: Lill
authors.forename: David A
authors.initials: DA
authors.lastname: Brummell
authors.forename: Tony K
authors.initials: TK
authors.lastname: McGhie
authors.forename: Ronan K-Y
authors.initials: RK
authors.lastname: Chen
authors.forename: Daryl D
authors.initials: DD
authors.lastname: Rowan
mesh_terms: D001937:Brassica / Q000737:chemistry* / Q000378:metabolism; D002853:Chromatography, Liquid; D008401:Gas Chromatography-Mass Spectrometry; D005961:Glucosinolates / Q000032:analysis* / Q000378:metabolism; D015394:Molecular Structure; D016566:Organoselenium Compounds / Q000032:analysis* / Q000378:metabolism; D064586:Selenic Acid; D018036:Selenium Compounds / Q000737:chemistry*
chemical_list: D005961:Glucosinolates; D016566:Organoselenium Compounds; D018036:Selenium Compounds; D064586:Selenic Acid