To investigate why Cu/Zn-SOD activity decreased in the higher-Pi
treatments, the content of several essential nutrient elements was
determined using the inductively coupled plasma atomic emission
spectroscopy (ICP-AES). The P content increased with increasing Pi
application (Figure
7a).
The content values of K, Ca, and Fe were not affected by Pi application
(Figure 7a), but those of Mg, Mn, Zn, and Cu increased with increasing
Pi application (Figure 7a).
To deduce nutrient availabilities within leaves, we next examined the
mRNA expressions of several metal deficiency-responsive genes, such asZIP4 (Ishimaru et al., 2005), IRO2 (Ogo et al., 2006) andCOPT1 (Yuan et al., 2011), which are expressed under Zn-, Fe-,
and Cu-deficient conditions, respectively. The ZIP4 andIRO2 expressions increased with increasing in Pi application
(Figure 7b), COPT1 expression showed no significant change with
varying Pi application conditions (Figure 7b). These results suggest
that excessive Pi application does not inhibit the metal transport to
leaves, but Zn- and Fe-deficiency occurs within cells under conditions
of excessive Pi application.