Biological nitrification inhibition in maize\u2014isolation and identification of hydrophobic inhibitors from root exudates

Junnosuke Otaka,Hiroshi Ono,Tadashi Yoshihashi,Guntur Venkata Subbarao

doi:10.1007/s00374-021-01577-x

Abstract

To control agronomic N losses and reduce environmental pollution, biological nitrification inhibition (BNI) is a promising strategy. BNI is an ecological phenomenon by which certain plants release bioactive compounds that can suppress nitrifying soil microbes. Herein, we report on two hydrophobic BNI compounds released from maize root exudation (1 and 2), together with two BNI compounds inside maize roots (3 and 4). On the basis of a bioassay-guided fractionation method using a recombinant nitrifying bacterium Nitrosomonas europaea, 2,7-dimethoxy-1,4-naphthoquinone (1, ED50 = 2 μM) was identified for the first time from dichloromethane (DCM) wash concentrate of maize root surface and named “zeanone.” The benzoxazinoid 2-hydroxy-4,7-dimethoxy-2H-1,4-benzoxazin-3(4H)-one (HDMBOA, 2, ED50 = 13 μM) was isolated from DCM extract of maize roots, and two analogs of compound 2, 2-hydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (HMBOA, 3, ED50 = 91 μM) and HDMBOA-β-glucoside (4, ED50 = 94 μM), were isolated from methanol extract of maize roots. Their chemical structures (1–4) were determined by extensive spectroscopic methods. The contributions of these four isolated BNI compounds (1–4) to the hydrophobic BNI activity in maize roots were 19%, 20%, 2%, and 4%, respectively. A possible biosynthetic pathway for zeanone (1) is proposed. These results provide insights into the strength of hydrophobic BNI activity released from maize root systems, the chemical identities of the isolated BNIs, and their relative contribution to the BNI activity from maize root systems.

Highlights

Nitrogen (N), a macronutrient required for crop plant growth, is an essential component of fertilizer for sustaining food production in modern productive agriculture (White and Brown 2010)
We describe the isolation and identification of hydrophobic Biological nitrification inhibition (BNI) compounds from the surface of maize roots which were recovered from the DCM-wash, together with BNI compounds inside maize roots using root tissue after the DCM-wash procedure and recovered by two different extraction solvents: DCM extract and methanol (MeOH) extract
We discovered zeanone (1, ED50 = 2 μM), a new naphthoquinone in nature, in maize root exudates as one of the major BNI components

Summary

Introduction

Nitrogen (N), a macronutrient required for crop plant growth, is an essential component of fertilizer for sustaining food production in modern productive agriculture (White and Brown 2010). 50% among the world’s three highest-production cereals, rice (16%), wheat (18%), and maize (16%) (Coskun et al 2017; Ladha et al 2016) Despite their benefits, approximately half of applied N fertilizers are leached from agricultural fields, which results in economic loss because of excess fertilizer application and low N use efficiency of crop plants (Halvorson et al 2014; Lassaletta et al 2014; Mueller et al 2014). Approximately half of applied N fertilizers are leached from agricultural fields, which results in economic loss because of excess fertilizer application and low N use efficiency of crop plants (Halvorson et al 2014; Lassaletta et al 2014; Mueller et al 2014) These major N losses from fertilized soil are caused by two microbial biochemical reactions: nitrification and denitrification (Bock et al 1995; Zumft 1997). Because NH4+ (electropositive) can be attracted to the negatively charged surface of

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Conclusion