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Keywords:

  • acid phosphatase;
  • δ18O of leaf water;
  • δ18O-PO4;
  • soybean;
  • structural P;
  • TCA-soluble reactive P (TCA P)

Summary

  • The objective of this study was to investigate the isotopic composition of oxygen bound to phosphate (δ18O-PO4) in different phosphorus (P) pools in plant leaves. As a model plant we used soybean (Glycine max cv Toliman) grown in the presence of ample P in hydroponic cultures.
  • The leaf blades were extracted with 0.3 M trichloroacetic acid (TCA) and with 10 M nitric acid. These extractions allowed measurement of the TCA-soluble reactive P (TCA P) that is rapidly cycled within the cell and the total leaf P. The difference between total leaf P and TCA P yielded the structural P which includes organic P compounds not extractable by TCA.
  • P uptake and its translocation and transformation within the soybean plants lead to an 18O enrichment of TCA P (δ18O-PO4 between 16.9 and 27.5‰) and structural P (δ18O-PO4 between 42.6 and 68.0 ‰) compared with 12.4‰ in the phosphate in the nutrient solution.
  • δ18O values of phosphate extracted from soybean leaves grown under optimal conditions are greater than the δ18O-PO4 values of the provided P source. Furthermore, the δ18O-PO4 of TCA P seems to be controlled by the δ18O of leaf water and the activity of inorganic pyrophosphatase or other pyrophosphatases.