Unravelling impact of Na+, Cl- and their respective transporter in detrimental effects 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 specific responses of the plant to Na+ and Cl- toxic ions remain unknown. Moreover, the roles of Na+/H+ antiport and cation-chloride-cotransporter in salt stresses still remain unclear. In 1st experiment, two distinct 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 and fluorescence related parameters; carbon (∆13C) and nitrogen (δ15N) isotope discrimination were analyzed. TOG5307 exhibited a higher level of resistance than TOG5949 in terms of growth and photosynthesis maintenance and control of Cl- and Na+ accumulation. NaCl was the most detrimental treatment, followed by Na+ -dominant treatment while Cl- -treatment had the lowest effect. Impact of Na+ and Cl- on considered parameters are additive. In 2nd experiment, the two contrasted cultivars (TOG5307 and TOG5949) were exposed during 3 days in nutrient solutions to 75 mM NaCl containing 100 µM amiloride (inhibitor of Na+-H+ antiporters) or 200 µM bumetanide (inhibitor cation-chloride-cotransporters). Amiloride increased Na+ accumulation in roots and leaves to a higher extent in salt-resistant TOG5307 than in salt-sensitive TOG5949. Bumetanide reduced Cl- accumulation in both cultivars as well as K+ accumulation in TOG5307 and Na+ accumulation in TOG5949. Cultivars exhibiting contrasting levels of salinity resistance are available in Oryza glaberrima and salt-tolerant genotypes may constitute a valuable source of gene for classical rice improvement