Enhanced Antioxidant Enzymes Are Associated with Reduced Hydrogen Peroxide in Barley Roots under Saline Stress

Antioxidant enzymes are related to the resistance tovarious abiotic stresses including salinity. Barley isrelatively tolerant to saline stress among crop plants, butlittle information is available on barley antioxidantenzymes under salinity stress. We investigated temporaland spatial responses of activities and isoform profiles ofsuperoxide dismutase (SOD), catalase (CAT), ascorbateperoxidase (APX), non-specific peroxidase (POX), andglutathione reductase (GR) to saline stress in barleyseedlings treated with 200 mM NaCl for 0, 1, 2, 5 days,respectively. In the control plant, hydrogen peroxidecontent was about 2-fold higher in the root than in theshoot. Under saline stress, hydrogen peroxide content wasdecreased drastically by 70% at 2 d after NaCl treatment(DAT) in the root. In the leaf, however, the content wasremained unchanged by 2 DAT and increased about 14 %at 5 DAT. In general, the activities of antioxidant enzymeswere increased in the root and shoot under saline stress.But the increase was more significant and consistent in theroot. The activities of SOD, CAT, APX, POX, and GR wereincreased significantly in the root within 1 DAT, andvarious elevated levels were maintained by 5 DAT. Amongthe antioxidant enzymes, CAT activity was increased themost drastically. The significant increase in the activities ofSOD, CAT, APX, POX, and GR in the NaCl-stressedbarley root was highly correlated with the increasedexpression of the constitutive isoforms as well as theinduced ones. The hydrogen peroxide content in the rootwas most highly correlated with the CAT activity, indicatingan increased role of CAT in hydrogen peroxidedetoxification under salinity stress. In addition, the resultssuggest the significance of temporal and spatial regulationof each antioxidant isoform in determining the competenceof the antioxidant capacity under saline stress. Keywords: