3.4 Decreased P causes reduction of P-containing glycolytic intermediates under Al stress
Because P is an important substrate in glycolysis, we examined the change of P and Pi in root tips in a time course of 2, 6, 24 and 72 h of Al treatments. P concentration in the root tips of XZ29 remained relatively constant over 72 h in Al treatment, whereas P levels in XZ9 decreased steadily throughout the treatment reaching 65% of control levels by 72 h (Figure 5a). Compared to the Al-free controls, Pi concentration in root tips of XZ29 increased significantly during the first 6 h of Al treatment and then returned to control levels between 24 and 72 h (Figure 5b). By contrast, Pi concentrations in root tips of XZ9 showed no increase after 6 h, but these were decreased to 65% of controls in 24 h and then remained stable at this lower level (Figure 5b).
The Al-induced changes of P and Pi concentrations showed similar pattern as the changes of glycolytic intermediates, with greater decreases occurring in XZ9 than XZ29 (Figures 4b, 5a, 5b). Also, there were positive correlations between the P and Pi concentrations and P-containing glycolytic intermediates (Figure 5c). Thus, we investigated the response of glycolytic intermediates levels to the addition of phosphate (150 μM KH2PO4) after 72 h in Al treatment. We found that the metabolites in Cluster 1 increased rapidly in both accessions (Figures 5d, S9; Table S7).