title: Response differences between Ectocarpus siliculosus populations to copper stress involve cellular exclusion and induction of the phytochelatin biosynthetic pathway.
abstract: Some populations of brown seaweed species inhabit metal-polluted environments and can develop tolerance to metal stress, but the mechanisms by which this is accomplished are still to be elucidated. To address this, the responses of two strains of the model brown alga Ectocarpus siliculosus isolated from sites with different histories of metal contamination exposed to total copper (CuT) concentrations ranging between 0 and 2.4 μM for 10 days were investigated. The synthesis of the metal-chelator phytochelatin (PCs) and relative levels of transcripts encoding the enzymes γ-glutamylcysteine synthetase (γ-GCS), glutathione synthase (GS) and phytochelatin synthase (PCS) that participate in the PC biosynthetic pathway were measured, along with the effects on growth, and adsorption and uptake of Cu. Growth of strain LIA, from a pristine site in Scotland, was inhibited to a greater extent, and at lower concentrations, than that of Es524, isolated from a Cu-contaminated site in Chile. Concentrations of intra-cellular Cu were higher and the exchangeable fraction was lower in LIA than Es524, especially at the highest exposure levels. Total glutathione concentrations increased in both strains with Cu exposure, whereas total PCs levels were higher in Es524 than LIA; PC2 and PC3 were detected in Es524 but PC2 only was found in LIA. The greater production and levels of polymerisation of PCs in Es524 can be explained by the up-regulation of genes encoding for key enzymes involved in the synthesis of PCs. In Es524 there was an increase in the transcripts of γ-GCS, GS and PCS, particularly under high Cu exposure, whereas in LIA4 transcripts of γ-GCS1 increased only slightly, γ-GCS2 and GS decreased and PCS did not change. The consequences of higher intra-cellular concentrations of Cu, lower production of PCs, and lower expression of enzymes involved in GSH-PCs synthesis may be contributing to an induced oxidative stress condition in LIA, which explains, at least in part, the observed sensitivity of LIA to Cu. Therefore, responses to Cu exposure in E. siliculosus relate to the contamination histories of the locations from where the strains were isolated and differences in Cu exclusion and PCs production are in part responsible for the development of intra-specific resistance.
authors.affiliation: School of Marine Science and Engineering, Faculty of Science and Environment, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK.
authors.forename: Francesca
authors.initials: F
authors.lastname: Roncarati
authors.affiliation: School of Marine Science and Engineering, Faculty of Science and Environment, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK; Departamento de Biología, Facultad de Química y Biología, Universidad de Santiago de Chile, casilla 40 correo 33, Santiago, Chile; Departamento de Medio Ambiente, Facultad de Ingeniería, Universidad de Playa Ancha, Casilla 34-V, Valparaíso, Chile.
authors.forename: Claudio A
authors.initials: CA
authors.lastname: Sáez
authors.affiliation: Laboratory of Plant Cyto-Physiology, University of Calabria, Arcavata di Rende, Cosenza 87036, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Greco
authors.affiliation: Helmholtz Centre for Ocean Research, GEOMAR, Wischhofstrasse 1-3, Build. 12, D-24148 Kiel, Germany.
authors.forename: Martha
authors.initials: M
authors.lastname: Gledhill
authors.affiliation: Laboratory of Plant Cyto-Physiology, University of Calabria, Arcavata di Rende, Cosenza 87036, Italy.
authors.forename: Maria B
authors.initials: MB
authors.lastname: Bitonti
authors.affiliation: School of Marine Science and Engineering, Faculty of Science and Environment, Plymouth University, Drake Circus, Plymouth PL4 8AA, UK. Electronic address: mtbrown@plymouth.ac.uk.
authors.forename: Murray T
authors.initials: MT
authors.lastname: Brown
mesh_terms: D019881:Aminoacyltransferases / Q000235:genetics / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000187:drug effects*; D002677:Chile; D003300:Copper / Q000032:analysis / Q000633:toxicity*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D005721:Glutamate-Cysteine Ligase / Q000235:genetics / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D000459:Phaeophyceae / Q000737:chemistry / Q000187:drug effects*; D054811:Phytochelatins / Q000235:genetics* / Q000378:metabolism; D013045:Species Specificity; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical; D003300:Copper; D054811:Phytochelatins; D019881:Aminoacyltransferases; C093784:glutathione gamma-glutamylcysteinyltransferase; D005721:Glutamate-Cysteine Ligase; D005978:Glutathione
keywords: Brown algae; Copper; Ectocarpus siliculosus; Glutathione; Inter-population variation; Phytochelatins