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

Salinity resistance of the African rice species (Oryza glaberrima) is poorly documented and the specific 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, fluorescence 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 efficiency. Most recorded physiological parameters were affected by both Na+ and Cl−. The pattern of modification induced by both types of toxicities was similar in the two studied cultivars which thus mainly differ 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 effect. The two considered cultivars mainly differ 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.