Phytoglobin Expression Alters the Na+/K+ Balance and Antioxidant Responses in Soybean Plants Exposed to Na2SO4

Abstract

Soybean (<i>Glycine max</i>) is an economically important crop which is very susceptible to salt stress. Tolerance to Na₂SO₄ stress was evaluated in soybean plants overexpressing or suppressing the phytoglobin <i>GmPgb1</i>. Salt stress depressed several gas exchange parameters, including the photosynthetic rate, caused leaf damage, and reduced the water content and dry weights. Lower expression of respiratory burst oxidase homologs (<i>RBOHB</i> and <i>D</i>), as well as enhanced antioxidant activity, resulting from <i>GmPgb1</i> overexpression, limited ROS-induced damage in salt-stressed leaf tissue. The leaves also exhibited higher activities of the H₂O₂-quenching enzymes, catalase (CAT) and ascorbate peroxidase (APX), as well as enhanced levels of ascorbic acid. Relative to WT and <i>GmPgb1</i>-suppressing plants, overexpression of <i>GmPgb1</i> attenuated the accumulation of foliar Na⁺ and exhibited a lower Na⁺/K⁺ ratio. These changes were attributed to the induction of the Na⁺ efflux transporter SALT OVERLY SENSITIVE 1 (SOS1) limiting Na⁺ intake and transport and the inward rectifying K⁺ channel POTASSIUM TRANSPORTER 1 (AKT1) required for the maintenance of the Na⁺/K⁺ balance.