Rice plants encode five Cu/Zn-SOD genes in their genomes (RiceXPro; http://ricexpro.dna.affrc.go.jp/). All mRNA expressions encoding Cu/Zn-SOD were determined on the leaf fresh weight and the 18S ribosome mRNA expression bases relative to those of the control-Pi plants respectively. The expression of cytCu/ZnSOD1,2 andCuZnSOD3 increased with increasing Pi application (Figure 6a-c), but those of perCuZnSOD and chlCuZnSOD were not affected by Pi application (Figure 6d, e). Thus, the responses of these mRNA expressions could not account for the decrease in Cu/Zn-SOD activity.