title: Selenium hyperaccumulation offers protection from cell disruptor herbivores.
abstract: BACKGROUND
  Hyperaccumulation, the rare capacity of certain plant species to accumulate toxic trace elements to levels several orders of magnitude higher than other species growing on the same site, is thought to be an elemental defense mechanism against herbivores and pathogens. Previous research has shown that selenium (Se) hyperaccumulation protects plants from a variety of herbivores and pathogens. Selenium hyperaccumulating plants sequester Se in discrete locations in the leaf periphery, making them potentially more susceptible to some herbivore feeding modes than others. In this study we investigate the protective function of Se in the Se hyperaccumulators Stanleya pinnata and Astragalus bisulcatus against two cell disrupting herbivores, the western flower thrips (Frankliniella occidentalis) and the two-spotted spider mite (Tetranychus urticae).
  
  
  RESULTS
  Astragalus bisulcatus and S. pinnata with high Se concentrations (greater than 650 mg Se kg(-1)) were less subject to thrips herbivory than plants with low Se levels (less than 150 mg Se kg(-1)). Furthermore, in plants containing elevated Se levels, leaves with higher concentrations of Se suffered less herbivory than leaves with less Se. Spider mites also preferred to feed on low-Se A. bisulcatus and S. pinnata plants rather than high-Se plants. Spider mite populations on A. bisulcatus decreased after plants were given a higher concentration of Se. Interestingly, spider mites could colonize A. bisulcatus plants containing up to 200 mg Se kg(-1) dry weight, concentrations which are toxic to many other herbivores. Selenium distribution and speciation studies using micro-focused X-ray fluorescence (μXRF) mapping and Se K-edge X-ray absorption spectroscopy revealed that the spider mites accumulated primarily methylselenocysteine, the relatively non-toxic form of Se that is also the predominant form of Se in hyperaccumulators.
  
  
  CONCLUSIONS
  This is the first reported study investigating the protective effect of hyperaccumulated Se against cell-disrupting herbivores. The finding that Se protected the two hyperaccumulator species from both cell disruptors lends further support to the elemental defense hypothesis and increases the number of herbivores and feeding modes against which Se has shown a protective effect. Because western flower thrips and two-spotted spider mites are widespread and economically important herbivores, the results from this study also have potential applications in agriculture or horticulture, and implications for the management of Se-rich crops.
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80532, USA.
authors.forename: Colin F
authors.initials: CF
authors.lastname: Quinn
authors.forename: John L
authors.initials: JL
authors.lastname: Freeman
authors.forename: Ray J B
authors.initials: RJ
authors.lastname: Reynolds
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Cappa
authors.forename: Sirine C
authors.initials: SC
authors.lastname: Fakra
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Marcus
authors.forename: Stormy D
authors.initials: SD
authors.lastname: Lindblom
authors.forename: Erin K
authors.initials: EK
authors.lastname: Quinn
authors.forename: Lindsay E
authors.initials: LE
authors.lastname: Bennett
authors.forename: Elizabeth A H
authors.initials: EA
authors.lastname: Pilon-Smits
mesh_terms: D000818:Animals; D027883:Astragalus Plant / Q000378:metabolism*; D019607:Brassicaceae / Q000378:metabolism*; D003545:Cysteine / Q000031:analogs & derivatives / Q000378:metabolism / Q000633:toxicity; D005518:Food Preferences; D007313:Insecta / Q000502:physiology*; D016566:Organoselenium Compounds / Q000378:metabolism / Q000633:toxicity; D012643:Selenium / Q000378:metabolism* / Q000633:toxicity; D017279:Selenocysteine / Q000031:analogs & derivatives; D040102:Tetranychidae / Q000502:physiology*
chemical_list: D016566:Organoselenium Compounds; D017279:Selenocysteine; D012643:Selenium; D003545:Cysteine; C002979:selenomethylselenocysteine
references.citation: New Phytol. 2005 Mar;165(3):763-71
references.pmid: 15720687
references.citation: New Phytol. 2004 Jun;162(3):655-662
references.pmid: 33873760
references.citation: Oecologia. 2008 Mar;155(2):267-75
references.pmid: 18278517
references.citation: New Phytol. 2001 Jan;149(1):61-69
references.pmid: 33853233
references.citation: Plant J. 2005 Jun;42(6):785-97
references.pmid: 15941393
references.citation: Nutr Cancer. 2010;62(1):66-73
references.pmid: 20043261
references.citation: New Phytol. 2002 Nov;156(2):145-169
references.pmid: 33873279
references.citation: New Phytol. 2005 Nov;168(2):331-44
references.pmid: 16219073
references.citation: Am J Bot. 2009 Jun;96(6):1075-85
references.pmid: 21628258
references.citation: J Evol Biol. 2010 Apr;23(4):797-804
references.pmid: 20149024
references.citation: Plant Physiol. 1981 May;67(5):1051-3
references.pmid: 16661781
references.citation: Curr Biol. 2006 Nov 21;16(22):2181-92
references.pmid: 17113382
references.citation: New Phytol. 2008;177(3):715-724
references.pmid: 18028291
references.citation: JAMA. 1996 Dec 25;276(24):1957-63
references.pmid: 8971064
references.citation: Am J Bot. 2002 Dec;89(12):1925-32
references.pmid: 21665621
references.citation: Plant Physiol. 2006 Sep;142(1):124-34
references.pmid: 16920881
references.citation: J Synchrotron Radiat. 2004 May 1;11(Pt 3):239-47
references.pmid: 15103110
references.citation: New Phytol. 2003 Aug;159(2):461-469
references.pmid: 33873368
references.citation: New Phytol. 2007;173(3):517-525
references.pmid: 17244046
references.citation: Science. 1978 Oct 13;202(4364):183-91
references.pmid: 17801907
references.citation: Annu Rev Biochem. 1990;59:111-27
references.pmid: 2142875
references.citation: New Phytol. 2007;175(2):363-369
references.pmid: 17587384
references.citation: Oncol Rep. 2007 Jan;17(1):209-16
references.pmid: 17143500
references.citation: Biochim Biophys Acta. 2009 Nov;1790(11):1478-85
references.pmid: 19268692