Phosphorus-deficiency reduces aluminium toxicity by altering uptake and metabolism of root zone carbon dioxide

The role of phosphorus (P) status in root-zone CO₂ utilisation for organic acid synthesis during Al³⁺ toxicity was assessed. Root-zone CO₂ can be incorporated into organic acids via Phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31). P-deficiency and Al³⁺ toxicity can induce organic acid synthesis, but it is unknown how P status affects the utilisation of PEPC-derived organic acids during Al³⁺ toxicity. Two-week-old Solanum lycopersicum seedlings were transferred to hydroponic culture for 3 weeks. The hydroponic culture consisted of a standard Long Ashton nutrient solution containing either 0.1 μM or 1 mM P. Short-term Al³⁺ toxicity was induced by a 60-min exposure to a pH-buffered solution (pH 4.5) containing 2 mM CaSO₄ and 50 μM AlCl₃. Al³⁺ toxicity induced a decline in root respiration, adenylate concentrations and an increase in root-zone CO₂ utilisation for both P sufficient and P-deficient plants. However during Al³⁺ toxicity, P deficiency enhanced the incorporation and metabolism of root-zone CO₂ via PEPC. Moreover, P deficiency led to a greater proportion of the PEPC-derived organic acids to be exuded during Al³⁺ toxicity. These results indicate that P-status can influence the response to Al³⁺ by inducing a greater utilisation of PEPC-derived organic acids for Al³⁺ detoxification.