Split-root assays for studying legume–rhizobia symbioses, rhizodeposition, and belowground nitrogen transfer in legumes

Abstract

Split-root assays have been used widely in studies focused on understanding the complex regulatory mechanisms in legume–rhizobia symbioses, root nitrogen rhizodeposition, and belowground nitrogen transfer, and the effects of different biotic/abiotic factors on this symbiotic interaction. This assay allows a plant to have a root system that is physically divided into two distinct sections that are both still attached to a common shoot. Thus, each root section can be treated separately to monitor local and systemic plant responses. Different techniques are used to establish split-root assemblies, including double-pot systems, divided growth pouches, elbow root assembly, twin-tube systems, a single pot or chamber with a partition in the center, and divided agar plates. This review is focused on discussing the various types of split-root assays currently used in legume-based studies, and their associated advantages and limitations. Furthermore, this review also focuses on how split-root assays have been used for studies on nitrogen rhizodeposition, belowground nitrogen transfer, systemic regulation of nodulation, and biotic and abiotic factors affecting legume–rhizobia symbioses.

The effect of drought stress on nodulation, plant growth, and nitrogen fixation in soybean during early plant growth

“…Also, soil water deficit can affect the initial establishment of symbiosis by disturbing the legume‐rhizobia molecular signal exchange (de Freitas et al, 2022). Moisture deficit in the soil can interrupt the exchange of plant‐derived flavonoids and rhizobial lipochito‐oligosaccharides, which are critical for successful nodulation in legumes (Thilakarathna & Cope, 2021). Our data show that although the number of nodules was reduced under drought stress, average nodule mass was increased.…”

The B-type response regulator GmRR11d mediates systemic inhibition of symbiotic nodulation

“…The split-root experiments were carried out by the methods as described previously 76 . The seven-day-old Bragg and nts1007 roots were divided into two parts and treated with (+R) or without (-R) B. diazoefficiens strain USDA110.…”

The Potential of Cold Plasma-Based Seed Treatments in Legume–Rhizobia Symbiotic Nitrogen Fixation: A Review

“…The initiation of root invasion involves signal exchange between legume roots and rhizobia [78]. Legume roots release flavonoid/isoflavonoid compounds that bind to bacterial NodD proteins [79,80]. This interaction activates the transcription of nod genes in rhizobia, resulting in the production of lipo-chitooligosaccharides, known as nodulation (Nod) factors [81].…”