Abstract
The microRNA miR398 of Arabidopsis play important roles in stress response and copper metabolism by post-transcriptionally down-regulating CuZn-SOD mRNA. It has been reported that under Cu-deficiency the up-regulated miR398 suppressed the biosynthesis of chloroplastic CuZn-SOD but induced alternative chloroplastic Fe-SOD. We have previously found that CuZn-SOD activity in maize was enhanced by the Cu-chelator trientine (TET). To elucidate this mechanism, we further investigated SOD gene expression in maize and rice after treatment of TET. Spermidine, that structurally resembles TET, and EDTA did not induce SOD in maize, indicating that the enhancement of maize SOD by TET is due to Cu-chelation. In TET treatments (1-10 mM, 24-48h), maize SOD activity was increased under both light and dark conditions but not was rice SOD. Photosynthetic activity during TET treatments, determined by chlorophyll fluorescence, was slightly lower under light than under dark. These data excludes the possibility of involvement of reactive oxygen species, since maize SOD was more enhanced under dark than light. Thus, it was suggested that SOD regulation via microRNA differs between C3 and C4 plants.
