Discriminating the impact of Na+ and Cl− in the deleterious efects of salt stress on the African rice species (Oryza glaberrima Steud.)

Abstract

Salinity resistance of the African rice species (Oryza glaberrima) is poorly documented and the specifc responses of the plant to Na+ and Cl− toxic ions remain unknown. Cultivars TOG5307 and TOG5949 were maintained for 15 days on iso-osmotic nutrient solutions containing 50 mM NaCl, or a combination of Cl− salts (Cl−-dominant) or Na+ salts (Na+-dominant). Plant water status, ion accumulation, gas exchange, fuorescence related parameters, carbon (δ13C) and nitrogen (δ15N) isotope ratios were analyzed. TOG5307 accumulated lower amounts of Na+ and Cl− in the shoot (1.63 and 1.49 µmol g−1 DW, respectively) than TOG 5949 (2.5 and 2.2 µmol g−1 DW). At 50 mM NaCl, TOG5307 also exhibited a higher net carbon assimilation rate (2.51 µmol CO2 m−2 s −1) than TOG5949 (1.51 µmol m−2 s −1) and a higher water use efciency. Most recorded physiological parameters were afected by both Na+ and Cl−. The pattern of modifcation induced by both types of toxicities was similar in the two studied cultivars which thus mainly difer for the quantitative aspects of the response rather than for the qualitative nature of the response. NaCl was the most detrimental treatment, followed by Na+-dominant treatment while Cl−-treatment had the lowest efect. The two considered cultivars mainly difer for their response to the ionic component of salt stress but not for their osmotic behaviour. The impact of Na+ and Cl− on considered parameters are additive, except for mineral nutrition where synergistic interactions were recorded for Na+ and S accumulation.