Detection, isolation and characterization of a root-exuded compound, methyl 3-(4-hydroxyphenyl) propionate, responsible for biological nitrification inhibition by sorghum (Sorghum bicolor)

  • Zakir H
  • Subbarao G
  • Pearse S
 et al. 
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Nitrification results in poor nitrogen (N) recovery and negative environmental impacts in most agricultural systems. Some plant species release secondary metabolites from their roots that inhibit nitrification, a phenomenon known as biological nitrification inhibition (BNI). Here, we attempt to characterize BNI in sorghum (Sorghum bicolor). In solution culture, the effect of N nutrition and plant age was studied on BNI activity from roots. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the inhibitory effect of root exudates. One major active constituent was isolated by activity-guided HPLC fractionations. The structure was analysed using NMR and mass spectrometry. Properties and the 70% inhibitory concentration (IC(70)) of this compound were determined by in vitro assay. Sorghum had significant BNI capacity, releasing 20 allylthiourea units (ATU) g(-1) root DW d(-1). Release of BNI compounds increased with growth stage and concentration of supply. NH4+ -grown plants released several-fold higher BNI compounds than NO3- -grown plants. The active constituent was identified as methyl 3-(4-hydroxyphenyl) propionate. BNI compound release from roots is a physiologically active process, stimulated by the presence of NH4+. Methyl 3-(4-hydroxyphenyl) propionate is the first compound purified from the root exudates of any species; this is an important step towards better understanding BNI in sorghum.

Author-supplied keywords

  • BNI compounds
  • Biological nitrification inhibition
  • Methyl 3-(4-hydroxyphenyl) propionate
  • NH4+
  • NO3-
  • Sorghum (Sorghum bicolor)

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  • Hossain A.K.M. Zakir

  • Guntur V. Subbarao

  • Stuart J. Pearse

  • Osamu Ito

  • Takayuki Ishikawa

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