Carbon Dioxide Improves Phosphorus Nutrition by Facilitating the Remobilization of Phosphorus From the Shoot Cell Wall in Rice ( Oryza sativa)

Phosphorus (P) starvation leads to increased reutilization of cell wall P in rice ( Oryza sativa). Carbon dioxide (CO ₂) is involved not only in plant growth and development but also in the response to abiotic stresses. However, it remains unclear whether CO ₂ affects the reutilization of cell wall P in rice when subjected to P deficiency. In the present study, elevated CO ₂ (600 μl·L ⁻¹) significantly increased the soluble P content in shoots when compared with ambient CO ₂ (400 μl·L ⁻¹). This positive effect was accompanied by an increase of pectin content, as well as an increase of pectin methylesterase (PME) activity, which results in P release from the shoot cell wall, making it available for plant growth. P deficiency significantly induced the expression of phosphate transporter genes ( OsPT2, OsPT6, and OsPT8) and decreased the P content in the xylem sap, but elevated CO ₂ had no further effect, indicating that the increased soluble P content observed in shoots under elevated CO ₂ is attributable to the reutilization of shoot cell wall P. Elevated CO ₂ further increased the P deficiency-induced ethylene production in the shoots, and the addition of the ethylene precursor 1-amino-cyclopropane-1-carboxylic acid (ACC) mimicked this effect, while the addition of the ethylene inhibitor aminoethoxyvinylglycine (AVG) abolished this effect. These results further support the role of ethylene in the alleviation of P deficiency under elevated CO ₂. Taken together, our results indicate that the improvement of P nutrition in rice by elevated CO ₂ is mediated by increasing the shoot cell wall pectin content and PME activity, possibly via the ethylene signaling pathway.