J Plant Ecol ›› 2013, Vol. 6 ›› Issue (2): 177-186.doi: 10.1093/jpe/rts017

• Research Articles • Previous Articles     Next Articles

Proline as a biochemical marker in relation to the ecology of two halophytic Juncus species

Monica Boscaiu1, Cristina Lull2, Josep Llinares3, Oscar Vicente4,* and Herminio Boira1   

  1. 1 Instituto Agroforestal Mediterráneo (IAM, UPV), Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain; 2 RE-FOREST, Departamento de Ingeniería Hidráulica y Medio Ambiente, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain; 3 Instituto de Investigación para la Gestión Integral de Zonas Costeras (IGIC, UPV), Universitat Politècnica de València, Calle Paranimf 1, 46730 Grau de Gandía, Valencia, Spain; 4 Instituto de Biología Molecular y Celular de Plantas (IBMCP, UPV-CSIC), Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain
  • Received:2011-11-18 Accepted:2012-05-12 Online:2012-08-20 Published:2013-03-26
  • Contact: Vicente, Oscar E-mail:ovicente@ibmcp.upv.es

Abstract: Aims Osmolytes, used for maintaining osmotic balance and as 'osmoprotectants', are synthesized in plants as a general, conserved response to abiotic stress, although their contribution to stress-tolerance mechanisms remains unclear. Proline, the most common osmolyte, accumulates in many plant species in parallel with increased external salinity and is considered a reliable biochemical marker of salt stress. We have measured proline levels in two halophytic, closely related Juncus species under laboratory and field conditions to assess the possible relevance of proline biosynthesis for salt tolerance and therefore for the ecology of these two taxa.
Methods Proline was quantified in plants treated with increasing NaCl concentrations and in plants sampled in two salt marshes located in the provinces of Valencia and Alicante, respectively, in southeast Spain. Electrical conductivity, pH, Na + and Cl ? concentrations were measured in soil samples collected in parallel with the plant material.
Important findings Treatment with NaCl inhibited growth of J. acutus plants in a concentration-dependent manner, but only under high salt conditions for J. maritimus. Salt treatments led to proline accumulation in both species, especially in the more salt-tolerant J. maritimus. The results, obtained under laboratory conditions, were confirmed in plants sampled in the field. In all the samplings, proline contents were significantly lower in J. acutus than in the more tolerant J. maritimus growing in the same area. No direct correlation between soil salinity and proline levels could be established, but seasonal variations were detected, with increased proline contents under accentuated water deficit conditions. Our results suggest that proline biosynthesis is not only an induced, general response to salt stress but also an important contributing factor in the physiological mechanisms of salt tolerance in Juncus, and that it therefore correlates with the ecology of both species.

Key words: halophytes, Juncus acutus, Juncus maritimus, osmolytes, salt stress

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