Roles of enzymes in anti-oxidative response system on three species of chenopodiaceous halophytes under NaCl-stress condition

Salinity is a major agricultural problem in the world. Reportedly, the scavenging of reactive oxygen species (ROS) plays a pivotal role for tolerance to salinity stress. While sodium chloride (NaCl) is very toxic for most plant species, some chenopodiaceous halophytes show a dependence on sodium (Na) for growth stimulation. This suggests that chenopodiaceous halophytes have an effective anti-oxidative response system (ARS). In this study, we aimed to research the contribution that anti-oxidative enzymes, super oxide dismutase (SOD), catalase (CAT), ascorbic acid peroxidase (APX), and glutathione reductase (GR) have on the growth stimulation of chenopodiaceous halophytes. We cultivated three species of chenopodiaceous halophytes, Suaeda salsa (L.) Pall., Kochia scoparia (L.) Schrad. and Swiss chard (Beta vulgaris (L.) var. cicla) in various NaCl concentration of 5, 50, 200 and 400 mM. Up to 200 mM, the specimens had no significant decrease in dry weight, although the exogenous Na enhanced the content of Na in the leaves and limited the accumulation of other cations. Moreover, at 200 mM NaCl, S. salsa significantly increased dry weight, but K. scoparia and Swiss chard did not show much growth stimulation. ROS-scavenging enzymes might have played pivotal roles, because up to 200 mM NaCl, all of the plant species did not increase their content of the oxidative stress marker, malondialdehyde (MDA). Among all the species, only CAT activity significantly correlated with dry weight. Additionally, APX activity correlated only with dry weight of Swiss chard. However, the growth stimulation of S. salsa at 200 mM NaCl could not be accounted for by water content, MDA and chlorophyll content. This is the first suggestion of CAT-dependent growth stimulation of chenopodiaceous halophytes under NaCl-stress conditions.