A dual isotopic approach using radioactive phosphorus and the isotopic composition of oxygen associated to phosphorus to understand plant reaction to a change in P nutrition.

BACKGROUND: Changing the phosphorus (P) nutrition leads to changes in plant metabolism. The aim of this study was to investigate how these changes are reflected in the distribution of33 P and the isotopic composition of oxygen associated to P (δ18 OP ) in different plant parts of soybean ( Glycine max cv. Toliman). Two P pools were extracted sequentially with 0.3 M trichloroacetic acid (TCA P) and 10 M nitric acid (HNO3 ; residual P).

RESULTS: The δ18 OP of TCA P in the old leaves of the - P plants (23.8‰) significantly decreased compared to the + P plants (27.4‰). The33 P data point to an enhanced mobilisation of P from residual P in the old leaves of the - P plants compared to the + P plants.

CONCLUSIONS: Omitting P for 10 days lead to a translocation of P from source to sink organs in soybeans. This was accompanied by a significant lowering of the δ18 OP of TCA P in the source organs due to the enzymatic hydrolysis of organic P. Combining33 P and δ18 OP can provide useful insights in plant responses to P omission at an early stage.