NaCl treatment markedly enhances H2O2-scavenging system in leaves of halophyte Suaeda salsa

The C-3 halophyte Suaeda salsa L. grown under the high concentration of NaCl (200 mM) was used to investigate the role of the hydrogen peroxide (H2O2)-scavenging system [catalase, ascorbate peroxidase, glutathione reductase (GR), ascorbic acid, and glutathione (GSH)] in removal of reactive oxygen species. The activity of catalase (CAT, EC 1.11.1.6), ascorbate peroxidase (APX, EC 1.11.1.11), and GR (EC 1.6.4.2) increased significantly after 7 days of NaCl treatment. The isoform patterns of CAT and GR were not affected, but the staining intensities were significantly increased by NaCl treatment. Activities of both the thylakoid-bound APX or GR and stromal APX (S-APX) or GR in the chloroplasts were markedly enhanced under high salinity. Fifty percent of APX in the chloroplasts is thylakoid-bound APX. S-APX and GR activity represented about 74-78 and 64-71% of the total soluble leaf APX and GR activity, respectively. Salt treatment increased the contents of ascorbic acid and GSH. By contrast, a decreased content of H2O2 was found in the leaves of NaCl-treated S. salsa. The level of membrane lipid peroxidation decreased slightly after NaCl treatment. The plants grew well with high rate of net photosynthesis under high salinity. These data suggest that upregulation of the H2O2-scavenging system in plant cells, especially in the chloroplasts, is at least one component of the tolerance adaptations of halophytes to high salinity.