Light interacts with salt stress in regulating superoxide dismutase gene expression in Arabidopsis

Arabidopsis thaliana plants (Col, Columbia, and N1438) were grown for 15 d under two light regimes providing different growth rates. The medium contained 0-85 mM NaCl. Shoot biomass and ion accumulation were measured. Superoxide dismutase (SOD) activity was assayed on gels, and the expression of six SOD genes was studied using real-time PCR. Mean growth rate was increased in high light (HL) regime as compared to low light (LL) regime. Parallely, most of SOD genes were overexpressed in Col and underexpressed in N1438 in response to HL. At 50 mM NaCl, plant growth was inhibited and a complex pattern of SOD gene expression was recorded. These responses varied according to the light regime, and differed between the accessions. This pattern, including the differences between the accessions, could be interpreted as a consequence of interaction between light and salt, hypothesizing that oxidative stress occurred when light energy input exceeded energy utilization when salt inhibited growth, and that oxidative stress induced overexpression of some SOD genes. Salt-induced excess Na+ accumulation in leaves and limitation of K+ provision to these organs might also participate in eliciting SOD genes' response. Variability was observed between the two accessions for all these traits.