title: Is salt stress tolerance in Casuarina glauca Sieb. ex Spreng. associated with its nitrogen-fixing root-nodule symbiosis? An analysis at the photosynthetic level.
abstract: Casuarina glauca is an actinorhizal tree which establishes root-nodule symbiosis with N2-fixing Frankia bacteria. This plant is commonly found in saline zones and is widely used to remediate marginal soils and prevent desertification. The nature of its ability to survive in extreme environments and the extent of Frankia contribution to stress tolerance remain unknown. Thus, we evaluated the ability of C. glauca to cope with salt stress and the influence of the symbiosis on this trait. To this end, we analysed the impact of salt on plant growth, mineral contents, water relations, photosynthetic-related parameters and non-structural sugars in nodulated vs. non-nodulated plants. Although the effects on photosynthesis and stomatal conductance started to become measurable in the presence of 200 mM NaCl, photochemical (e.g., photosynthetic electron flow) and biochemical (e.g., activity of photosynthetic enzymes) parameters were only strongly impaired when NaCl levels reached 600 mM. These results indicate the maintenance of high tissue hydration under salt stress, probably associated with enhanced osmotic potential. Furthermore, the maintenance of photosynthetic assimilation potential (A(max)), together with the increase in the quantum yield of down-regulated energy dissipation of PSII (Y(NPQ)), suggested a down-regulation of photosynthesis instead of photo-damaging effects. A comparison of the impact of increasing NaCl levels on the activities of photosynthetic (RubisCO and ribulose-5 phosphate kinase) and respiratory (pyruvate kinase and NADH-dependent malate dehydrogenase) enzymes vs. photosynthetic electron flow and fluorescence parameters, revealed that biochemical impairments are more limiting than photochemical damage. Altogether, these results indicate that, under controlled conditions, C. glauca tolerates high NaCl levels and that this capacity is linked to photosynthetic adjustments.
authors.affiliation: Grupo Interações Planta-Ambiente & Biodiversidade (PlantStress&Biodiversity), Instituto de Investigação Científica Tropical, Universidade de Lisboa, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal. Electronic address: pbbsantos@iict.pt.
authors.forename: Paula
authors.initials: P
authors.lastname: Batista-Santos
authors.affiliation: Grupo Interações Planta-Ambiente & Biodiversidade (PlantStress&Biodiversity), Instituto de Investigação Científica Tropical, Universidade de Lisboa, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal; Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. República, Quinta do Marquês, 2780-157, Oeiras, Portugal. Electronic address: nuno.duro@itqb.unl.pt.
authors.forename: Nuno
authors.initials: N
authors.lastname: Duro
authors.affiliation: Centro de Estudos Florestais, Instituto Superior de Agronomia, Universidade de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal. Electronic address: anadr@isa.ulisboa.pt.
authors.forename: Ana P
authors.initials: AP
authors.lastname: Rodrigues
authors.affiliation: Unidade Estratégica de Investigação e Serviços de Biotecnologia e Recursos Genéticos, Instituto Nacional de Investigação Agrária e Veterinária, I.P. (INIAV), Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal. Electronic address: jose.semedo@iniav.pt.
authors.forename: José N
authors.initials: JN
authors.lastname: Semedo
authors.affiliation: Grupo Interações Planta-Ambiente & Biodiversidade (PlantStress&Biodiversity), Instituto de Investigação Científica Tropical, Universidade de Lisboa, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal. Electronic address: palves66@hotmail.com.
authors.forename: Paula
authors.initials: P
authors.lastname: Alves
authors.affiliation: Grupo Interações Planta-Ambiente & Biodiversidade (PlantStress&Biodiversity), Instituto de Investigação Científica Tropical, Universidade de Lisboa, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal; Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. República, Quinta do Marquês, 2780-157, Oeiras, Portugal. Electronic address: mario.costa@itqb.unl.pt.
authors.forename: Mário
authors.initials: M
authors.lastname: da Costa
authors.affiliation: Grupo Interações Planta-Ambiente & Biodiversidade (PlantStress&Biodiversity), Instituto de Investigação Científica Tropical, Universidade de Lisboa, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal. Electronic address: ines.graca@iict.pt.
authors.forename: Inês
authors.initials: I
authors.lastname: Graça
authors.affiliation: Unidade Estratégica de Investigação e Serviços de Biotecnologia e Recursos Genéticos, Instituto Nacional de Investigação Agrária e Veterinária, I.P. (INIAV), Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal. Electronic address: isabel.pais@iniav.pt.
authors.forename: Isabel P
authors.initials: IP
authors.lastname: Pais
authors.affiliation: Unidade Estratégica de Investigação e Serviços de Biotecnologia e Recursos Genéticos, Instituto Nacional de Investigação Agrária e Veterinária, I.P. (INIAV), Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal. Electronic address: paula.scotti.afonso@hotmail.com.
authors.forename: Paula
authors.initials: P
authors.lastname: Scotti-Campos
authors.affiliation: GeoBioTec, Departamento Ciências da Terra, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Monte de Caparica, Portugal. Electronic address: fjl@fct.unl.pt.
authors.forename: Fernando C
authors.initials: FC
authors.lastname: Lidon
authors.affiliation: Grupo Interações Planta-Ambiente & Biodiversidade (PlantStress&Biodiversity), Instituto de Investigação Científica Tropical, Universidade de Lisboa, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal; GeoBioTec, Departamento Ciências da Terra, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Monte de Caparica, Portugal. Electronic address: antonio.leitao@iict.pt.
authors.forename: António E
authors.initials: AE
authors.lastname: Leitão
authors.affiliation: Department of Ecology, Environment and Plant Sciences, Stockholm University, 106 91 Stockholm, Sweden. Electronic address: Katharina.Pawlowski@botan.su.se.
authors.forename: Katharina
authors.initials: K
authors.lastname: Pawlowski
authors.affiliation: Grupo Interações Planta-Ambiente & Biodiversidade (PlantStress&Biodiversity), Instituto de Investigação Científica Tropical, Universidade de Lisboa, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal; Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. República, Quinta do Marquês, 2780-157, Oeiras, Portugal. Electronic address: aribeiro@itqb.unl.pt.
authors.forename: Ana I
authors.initials: AI
authors.lastname: Ribeiro-Barros
authors.affiliation: Grupo Interações Planta-Ambiente & Biodiversidade (PlantStress&Biodiversity), Instituto de Investigação Científica Tropical, Universidade de Lisboa, Av. República, Quinta do Marquês, 2784-505 Oeiras, Portugal; GeoBioTec, Departamento Ciências da Terra, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, Campus da Caparica, 2829-516 Monte de Caparica, Portugal. Electronic address: cochichor@mail.telepac.pt.
authors.forename: José C
authors.initials: JC
authors.lastname: Ramalho
mesh_terms: D004579:Electron Transport; D019684:Magnoliopsida / Q000502:physiology*; D009586:Nitrogen Fixation; D010788:Photosynthesis; D018517:Plant Roots / Q000502:physiology*; D012492:Salts; D013312:Stress, Physiological; D013559:Symbiosis; D020524:Thylakoids / Q000378:metabolism
chemical_list: D012492:Salts
keywords: Actinorhizal nodules; Casuarina glauca; Frankia; Photosynthesis; Salt stress