Phytoglobin Expression Alters the Na + /K + Balance and Antioxidant Responses in Soybean Plants Exposed to Na 2 SO 4 .

Soybean ( Glycine max ) is an economically important crop which is very susceptible to salt stress. Tolerance to Na 2 SO 4 stress was evaluated in soybean plants overexpressing or suppressing the phytoglobin GmPgb1 . 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 ( RBOHB and D ), as well as enhanced antioxidant activity, resulting from GmPgb1 overexpression, limited ROS-induced damage in salt-stressed leaf tissue. The leaves also exhibited higher activities of the H 2 O 2 -quenching enzymes, catalase (CAT) and ascorbate peroxidase (APX), as well as enhanced levels of ascorbic acid. Relative to WT and GmPgb1 -suppressing plants, overexpression of GmPgb1 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.