Is salt stress tolerance in Casuarina glauca Sieb. ex Spreng. associated with its nitrogen-fixing root-nodule symbiosis? An analysis at the photosynthetic level

Paula Batista-Santos, Nuno Duro, Ana P. Rodrigues, José N. Semedo, Paula Alves, Mário da Costa, Inês Graça, Isabel P. Pais, Paula Scotti-Campos, Fernando José Cebola Lidon, António E. Leitão, Katharina Pawlowski, Ana I. Ribeiro-Barros, José C. Ramalho

Research output: Contribution to journalArticle

17 Citations (Scopus)

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 200mM NaCl, photochemical (e.g., photosynthetic electron flow) and biochemical (e.g., activity of photosynthetic enzymes) parameters were only strongly impaired when NaCl levels reached 600mM. 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 (Amax), together with the increase in the quantum yield of down-regulated energy dissipation of PSII (YNPQ), 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.

Original languageEnglish
Pages (from-to)97-109
Number of pages13
JournalPlant Physiology And Biochemistry
Volume96
DOIs
Publication statusPublished - 1 Nov 2015

Keywords

  • Actinorhizal nodules
  • Casuarina glauca
  • Frankia
  • Photosynthesis
  • Salt stress

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