Biological nitrification inhibition (BNI) activity in sorghum and its characterization

Subbarao, G V and Nakahara, K and Ishikawa, T and Ono, H and Yoshida, M and Yoshihashi, T and Zhu, Y and Zakir, H A K M and Deshpande, S P and Hash, C T and Sahrawat, K L (2013) Biological nitrification inhibition (BNI) activity in sorghum and its characterization. Plant and Soil, 366 (1-2). pp. 243-259. ISSN 0032-079X

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Abstract

Aims The ability to suppress soil nitrification through the release of nitrification inhibitors from plant roots is termed ‘biological nitrification inhibition’ (BNI). Here, we aimed at the quantification and characterization of the BNI function in sorghum that includes inhibitor production, their chemical identity, functionality and factors regulating their release. Methods Sorghum was grown in solution culture and root exudate was collected using aerated NH4Cl solutions. A bioluminescence assay using recombinant Nitrosomonas europaea was employed to determine the BNI activity. Activity-guided chromatographic fractionation was used to isolate biological nitrification inhibitors (BNIs). The chemical structure was analyzed using NMR and mass spectrometry; pH-stat systems were deployed to analyze the role of rhizosphere pH on BNIs release. Results Sorghum roots released two categories of BNIs: hydrophilic- and hydrophobic-BNIs. The release rates for hydrophilic- and hydrophobic- BNIs ranged from 10 to 25 ATU g−1 root dwt. d−1. Addition of hydrophilic BNIs (10 ATU g−1 soil) significantly inhibited soil nitrification (40 % inhibition) during a 30-d incubation test. Two BNI compounds isolated are: sakuranetin (ED80 0.6 μM; isolated from hydrophilic-BNIs fraction) and sorgoleone (ED80 13.0 μM; isolated from hydrophobic-BNIs fraction), which inhibited Nitrosomonas by blocking AMO and HAO enzymatic pathways. The BNIs release required the presence of NH4+ in the root environment and the stimulatory effect of NH4+ lasted 24 h. Unlike the hydrophobic-BNIs, the release of hydrophilic-BNIs declined at a rhizosphere pH >5.0; nearly 80 % of hydrophilic-BNI release was suppressed at pH ≥7.0. The released hydrophilic-BNIs were functionally stable within a pH range of 5.0 to 9.0. Sakuranetin showed a stronger inhibitory activity (ED50 0.2 μM) than methyl 3-(4-hydroxyphenyl) propionate (MHPP) (ED50 100 μM) (isolated from hydrophilic-BNIs fraction) in the in vitro culture-bioassay, but the activity was non-functional and ineffective in the soil-assay. Conclusions There is an urgent need to identify sorghum genetic stocks with high potential to release functional-BNIs for suppressing nitrification and to improve nitrogen use efficiency in sorghum-based production systems.

Item Type:	Article
Divisions:	RP-Dryland Cereals
CRP:	CGIAR Research Program on Dryland Cereals
Uncontrolled Keywords:	Activity-guided isolation – Ammonia monooxygenase (AMO) – Biological nitrification inhibition (BNI) – BNI compounds – HAO (hydroxylamine oxidoreductase) – Hydrophilic and hydrophobic nitrification inhibitors – Sakuranetin – Sorghum – Sorgoleone
Subjects:	Mandate crops > Sorghum Others > Plant Pathology
Depositing User:	Mr Sanat Kumar Behera
Date Deposited:	01 Sep 2012 08:34
Last Modified:	19 Oct 2016 05:52
URI:	http://oar.icrisat.org/id/eprint/6105
Official URL:	http://dx.doi.org/10.1007/s11104-012-1419-9
Projects:	UNSPECIFIED
Funders:	Natural Science Foundation of China
Acknowledgement:	We acknowledge the technical assistance of Ms. N. Kudo and Ms. Notazawa in the conduct of various experiments described in this manuscript. We acknowledge the cooperation and funding support from Natural Science Foundation of China (NSFC 31172035) to one of the co-authors Yiyong Zhu. We thank Dr. Wade Berry, Univ. of California, LA, USA who read an earlier version of this manuscript and offered suggestions to help with the interpretation of results presented.
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