IMP2RIS, an automated plant root PET radiotracer gas delivery system for in-soil visualization of symbiotic N2 fixation in nodulated roots of soybean plants via PET imaging

The real-time and non-invasive visualization and quantification of symbiotic nitrogen fixation (SNF) in nodulated roots of soybean plants using Positron Emission Tomography (PET) imaging, coupled with the application of [¹³N]N₂ gas as a PET radiotracer, has been explored in only a few studies. In these studies, [¹³N]N₂ was delivered to nodulated soybean roots suspended in air within gas-tight acrylic boxes, followed by two-dimensional (2D) PET imaging to visualize the assimilated [¹³N]N₂ in the air-suspended root nodules. In this paper, we introduce the In-Media Plant PET Root Imaging System (IMP²RIS), a novel gas delivery system designed and constructed in-house. Unlike the previous methods, IMP²RIS allows for non-intrusive delivery and exposure of [¹³N]N₂ gas to the nodulated roots of soybean plants grown in a clay-rich, soil-like and visually opaque growth medium. This advancement enabled in-soil, three-dimensional (3D) visualization of SNF in soybean root nodules using Sofie, a preclinical PET scanner. Equipped with automated controls, IMP²RIS ensures ease of operation and operator safety during the [¹³N]N₂ delivery process. We describe the components and functionalities of IMP²RIS, supported by experimental results showcasing its successful application in efficient delivery and exposure of [¹³N]N₂ gas to nodulated roots of three soybean plant cultivars that vary in rates of N₂ fixation. The in-soil quantitative PET imaging of SNF, aided by IMP²RIS, holds promise for enhancing the integration of SNF as a functional phenotypic trait into breeding programs, aiming to enhance SNF efficiency by identifying breeding materials with high SNF capacities.