A comprehensive study of the proteins involved in salinity stress response in roots and shoots of the FL478 genotype of rice (Oryza sativa L. ssp. indica)

Rice, a major staple, is the most salt-sensitive cereal. High salinity triggers several adaptive responses in rice to cope with osmotic and ionic stress at the physiological, cellular, and molecular levels. A major QTL for salinity tolerance, named Saltol, is present on chromosome 1 of Indian landraces such as Pokkali and Nona Bokra. The early proteomic and physiological responses to salinity in roots and shoots of FL478, an inbred rice line harboring the Saltol QTL, were characterized. Plantlets were cultured in hydroponic cultures with 100 mmol L⁻¹ NaCl and evaluated at 6, 24, and 48 h. At the physiological level, root length significantly increased at 48 h, whereas shoot length was reduced. The Na⁺/K⁺ ratio was maintained at lower levels in shoots than in roots, suggesting that roots play a protective role. More than 2000 proteins were detected in both tissues. Roots showed a faster and more coordinated proteomic response than shoots, evident after only 6 h of treatment. These responses showed clear correspondence with those of proteins involved in transcription and translation. Maintenance of mitochondrial activity and amino acid metabolism in roots, and activation of stress-responsive proteins such as dehydrins and PLAT in shoots, may play a key role during the response of the plant to salinity stress. Proteomic and physiological responses showed that roots respond in a more highly adaptive manner than shoots to salinity stress, suggesting that this tissue is critical to the tolerance observed in cultivars harboring Saltol.