Relationship of Salinity Tolerance to Na + Exclusion, Proline Accumulation, and Antioxidant Enzyme Activity in Rice Seedlings

Rice is a staple crop for over 50% of the world’s population, but its sensitivity to salinity poses a threat to meeting the worldwide demand. This study investigated the correlation of salinity tolerance to Na + exclusion, proline accumulation, and the activity of antioxidant enzymes in some rice cultivars originating from Egypt. Giza 182 was shown to be the most tolerant of the five cultivars, as judged by visual symptoms of salt injury, growth parameters, and patterns of Na + accumulation, while Sakha 105 appeared to be highly susceptible. In detail, Giza 182 accumulated the lowest Na + concentration and maintained a much lower Na + /K + ratio in all plant organs in comparison to Sakha 105. The salinity-tolerant varieties had higher accumulation of proline than the salinity-susceptible cultivars. The salinity-tolerant Giza 182 accumulated a higher concentration of proline, but the lipid peroxidation (MDA) level was significantly reduced compared to in the salinity-susceptible Sakha 105. In addition, Giza 182 had stronger activity of both catalase (CAT) and ascorbate peroxidase (APX) compared to Sakha 105. The findings of this study reveal that the salinity tolerance in rice is primarily attributable to Na + exclusion, the accumulation of proline in rice organs, a low Na + /K + ratio, and a low level of lipid peroxidation. The levels of the antioxidant enzymes CAT and APX and the accumulation of proline may play important roles in salinity tolerance in rice. However, the comparative involvement of individual antioxidant enzymes in salinity stress in rice should be further investigated. Giza 182 has the potential to be cultivated in salinity-affected areas, although the effects of salinity stress on its grain yield and quality should be evaluated during the full crop cycle.