A solid-state membrane potentiometric microsensor for in situ sensing of NH 4 + in soybean root nodules.

Abstract

Soybean-rhizobia symbiotic nitrogen fixation, a process in which rhizobia mediate biological nitrogen fixation by converting inert atmospheric nitrogen (N 2 ) into biologically available forms (e.g., ammonium, NH 4 + ), has been extensively investigated. However, non-invasive, in situ monitoring methods for this process remain lacking. Herein, we report a solid-state membrane potentiometric ammonium ion-selective microelectrode (NH 4 + -ISμE) for the in situ detection of NH 4 + in soybean root nodules. A Prussian blue analogue with ion channels, which enables the specific insertion/extraction of NH 4 + ions while excluding interfering cations, was electrodeposited on a carbon fiber to fabricate the microelectrode. The cation sorption capability and ion selectivity of the thin film were explored by modulating the intercalation/deintercalation process and reducing the interfering cations within the framework. The NH 4 + -ISμE exhibits a Nernstian response to NH 4 + over the concentration range of 1.0 × 10 -6 to 1.0 × 10 -3 M, with a detection limit of 6.2 × 10 -7 M. This sensor enables in situ, real-time detection of NH 4 + -the direct product of biological nitrogen fixation in the legume plant-rhizobium symbiotic system. The release of NH 4 + ions in soybean root nodules during nitrogen fixation was successfully monitored. Overall, this work provides a simple and versatile tool for studying and monitoring biological symbiotic nitrogen fixation processes.

Plant phenotyping relevance

ダイズ根粒内のアンモニウムと窒素固定状態を非侵襲・リアルタイムに測定する新規マイクロセンサーを開発し、性能評価と植物体内での実証を行っており、植物生理状態の取得法が中心である。

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