Extraction of P solubilizing active substances from the cell wall of groundnut roots

Groundnut can take up more phosphorus (P) from a low P soil that hardly contains plant available iron-bound P (Fe-P) as its major P form than other crops. This is considered to be caused by the presence of substances in the root cell wall (CW) that are able to solubilize P. A method for extraction of these phosphorus solubilizing active substances (PSAS) from the root CW of groundnut is described in this paper. Acid, alkaline and water extractants were used, but only a treatment with 1 M NaOH at 80 degreesC for 24 h was found to be appropriate to extract the PSAS from the root CW. The characteristics of the CW and the extracted CW components were compared. The P solubilizing activity of both decreased sharply after addition of Fe3+, whereas Ca2+ and Mg2+ had no effect. This similarity in chemical characteristics suggested that we had successfully extracted the active substances in the CW. Phosphorus-solubilizing compounds were also extracted from the root CW of other crops like soybean, pigeon pea and maize, but these other crops contained less PSAS than groundnut. Using gel permeation and anion exchange column chromatography, the CW components were purified for HPLC analysis. The HPLC analyses indicated that two common retention times for the active substances existed for all four crops. The significance of the root CW in plant P nutrition is discussed.