Discriminating the effects of anionic components of salt stress in rice (Oryza sativa L.) : comparison between NaCl and Na2SO4 toxicities by Willy Irakoze

Salinity is a major abiotic stress limiting crop production and rice (Oryza sativa L.) is extremely salt-sensitive. As NaCl represents the major soluble salt causing soil salinity in the world, most studies dealing with plant responses to salt focus on NaCl. An excess of sulfate salts, however, may also affect some areas and this is especially the case of Rusizi plain (the most rice-producing area in Burundi) which is deeply affected by Na2SO4 salinity. Rice responses to Na2SO4 salinity only received minor attention and the global aim of our study was to compare the NaCl and Na2SO4 effects on rice physiological, biochemical and molecular parameters under controlled conditions as well as in field environment. Three rice cultivars were used throughout our study: Pokkali (salt-tolerant), I Kong Paô and V14 (salt-sensitive). At same Na+concentrations, NaCl was more toxic than Na2SO4 at all developmental phases. Higher accumulation of sodium was recorded in NaCl- than in Na2SO4-treated plants and Cl- accumulation in NaCl-treated plants was higher than S6+ accumulation in Na2SO4-exposed ones. Both salt stresses hampered to different extent plant growth, photosynthesis, water status and ion nutrition as well as oxidative status, leading to a decrease in yield-related parameters recorded in greenhouse and field conditions. Rice responses to NaCl and Na2SO4 salinities partly relied on specific gene expression as revealed by a holistic transcriptomic approach. Expression of genes coding for Na+ transport only partly explained the different behavior exhibited by plants exposed to NaCl and to Na2SO4. Sodium sulfate was shown to induce or increase the expression of a large number of stress-related genes while NaCl had mainly an inhibitory effect on gene expression. It is concluded that rice response to Na2SO4 involve specific targets and this study could be useful for rice crop improvement programs aiming to recover lost areas in Rusizi plain.

Willy Irakoze is a bioengineer, trained in plant pathology (2014, UCLouvain). In 2015, he began his PhD training in plant physiology at UCLouvain. He is a lecturer and researcher at the University of Burundi.