title: Interaction of plant growth regulators and reactive oxygen species to regulate petal senescence in wallflowers (Erysimum linifolium).
abstract: BACKGROUND
  In many species floral senescence is coordinated by ethylene. Endogenous levels rise, and exogenous application accelerates senescence. Furthermore, floral senescence is often associated with increased reactive oxygen species, and is delayed by exogenously applied cytokinin. However, how these processes are linked remains largely unresolved. Erysimum linifolium (wallflower) provides an excellent model for understanding these interactions due to its easily staged flowers and close taxonomic relationship to Arabidopsis. This has facilitated microarray analysis of gene expression during petal senescence and provided gene markers for following the effects of treatments on different regulatory pathways.
  
  
  RESULTS
  In detached Erysimum linifolium (wallflower) flowers ethylene production peaks in open flowers. Furthermore senescence is delayed by treatments with the ethylene signalling inhibitor silver thiosulphate, and accelerated with ethylene released by 2-chloroethylphosphonic acid. Both treatments with exogenous cytokinin, or 6-methyl purine (which is an inhibitor of cytokinin oxidase), delay petal senescence. However, treatment with cytokinin also increases ethylene biosynthesis. Despite the similar effects on senescence, transcript abundance of gene markers is affected differentially by the treatments. A significant rise in transcript abundance of WLS73 (a putative aminocyclopropanecarboxylate oxidase) was abolished by cytokinin or 6-methyl purine treatments. In contrast, WFSAG12 transcript (a senescence marker) continued to accumulate significantly, albeit at a reduced rate. Silver thiosulphate suppressed the increase in transcript abundance both of WFSAG12 and WLS73. Activity of reactive oxygen species scavenging enzymes changed during senescence. Treatments that increased cytokinin levels, or inhibited ethylene action, reduced accumulation of hydrogen peroxide. Furthermore, although auxin levels rose with senescence, treatments that delayed early senescence did not affect transcript abundance of WPS46, an auxin-induced gene.
  
  
  CONCLUSIONS
  A model for the interaction between cytokinins, ethylene, reactive oxygen species and auxin in the regulation of floral senescence in wallflowers is proposed. The combined increase in ethylene and reduction in cytokinin triggers the initiation of senescence and these two plant growth regulators directly or indirectly result in increased reactive oxygen species levels. A fall in conjugated auxin and/or the total auxin pool eventually triggers abscission.
authors.affiliation: School of Biosciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3TL, UK.|Current address: Faculty of Biosciences and Medical Engineering, Universiti Teknologi Malaysia, 81310, Johor Bahru, Johor, Malaysia.
authors.forename: Faezah Mohd
authors.initials: FM
authors.lastname: Salleh
authors.affiliation: Department of Biology, University of Pisa, Via Ghini 5, 56126, Pisa, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Mariotti
authors.affiliation: School of Biosciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3TL, UK.
authors.forename: Natasha D
authors.initials: ND
authors.lastname: Spadafora
authors.affiliation: School of Biosciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3TL, UK.|Current address: Queen Mary University of London, Mile End Road, London, E1 4NS, UK.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Price
authors.affiliation: Department of Agriculture, Food and Environment, University of Pisa, Via del Borghetto 80, 56124, Pisa, Italy.
authors.forename: Piero
authors.initials: P
authors.lastname: Picciarelli
authors.affiliation: Department of Food and Nutritional Sciences, University of Reading, Whiteknights, PO Box 226, Reading, Berkshire, RG6 6AP, UK.
authors.forename: Carol
authors.initials: C
authors.lastname: Wagstaff
authors.affiliation: Department of Biology, University of Pisa, Via Ghini 5, 56126, Pisa, Italy.
authors.forename: Lara
authors.initials: L
authors.lastname: Lombardi
authors.affiliation: School of Biosciences, Cardiff University, Main Building, Park Place, Cardiff, CF10 3TL, UK. rogershj@cardiff.ac.uk.
authors.forename: Hilary
authors.initials: H
authors.lastname: Rogers
mesh_terms: D003583:Cytokinins / Q000378:metabolism; D032601:Erysimum / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D005030:Ethylenes / Q000378:metabolism; D035264:Flowers / Q000254:growth & development / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D007210:Indoleacetic Acids / Q000378:metabolism; D010937:Plant Growth Regulators / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors
chemical_list: D003583:Cytokinins; D005030:Ethylenes; D007210:Indoleacetic Acids; D010937:Plant Growth Regulators; D017382:Reactive Oxygen Species; C036216:ethylene
keywords: Auxin; Cytokinin; Ethylene; Floral senescence; Reactive oxygen species; Transcript abundance; Wallflowers