Amino acid transporter mutants of Arabidopsis provides evidence that a non‐mycorrhizal plant acquires organic nitrogen from agricultural soil

Abstract

Although organic nitrogen (N) compounds are ubiquitous in soil solutions, their potential role in plant N nutrition has been questioned. We performed a range of experiments on Arabidopsis thaliana genetically modified to enhance or reduce root uptake of amino acids. Plants lacking expression of the Lysine Histidine Transporter 1 (LHT1) displayed significantly lower contents of C and N label and of U- C , N L-glutamine, as determined by liquid chromatography-mass spectrometry when growing in pots and supplied with dually labelled L-glutamine compared to wild type plants and LHT1-overexpressing plants. Slopes of regressions between accumulation of C-labelled carbon and N-labelled N were higher for LHT1-overexpressing plants than wild type plants, while plants lacking expression of LHT1 did not display a significant regression between the two isotopes. Uptake of labelled organic N from soil tallied with that of labelled ammonium for wild type plants and LHT1-overexpressing plants but was significantly lower for plants lacking expression of LHT1. When grown on agricultural soil plants lacking expression of LHT1 had the lowest, and plants overexpressing LHT1 the highest C/N ratios and natural δ N abundance suggesting their dependence on different N pools. Our data show that LHT1 expression is crucial for plant uptake of organic N from soil.

Source and sink mechanisms of nitrogen transport and use

“…LHTs are assumed to be high-affinity transport systems. LHT1 imports neutral and acidic amino acids into the root (Chen & Bush, 1997;Hirner et al, 2006;Svennerstam et al, 2007;Ganeteg et al, 2017), but also seems to transport the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (Shin et al, 2015). LHT6 acquires acidic amino acids, glutamine and alanine from the rhizosphere (Perchlik et al, 2014).…”

A microdialysis perspective of soil nitrogen availability

“…Miller, 1912, Lathrop, 1917). There is now significant evidence that plants can access a variety of soil organic N, including protein (Paungfoo-Lonhienne et al, 2008), DNA (Paungfoo-Lonhienne et al, 2010), peptides , Komarova et al, 2008 and amino acids (Wright, 1962, Kielland, 1994, Näsholm et al, 1998, Jamtgard et al, 2008, Warren and Adams, 2007, Vinall et al, 2012, Ganeteg et al, 2017. This understanding of the diversity of N forms potentially available to plants must change our approach to the relationship between N cycling and plant uptake.…”

“…As the technique measures a 'diffusive flux' of solutes in soil solution under near-undisturbed conditions, using probe dimensions similar to a plant root, we hypothesise that the technique provides a more relevant perspective of N availability in soil environments. The technique has already provided surprising results, particularly the greater relative contribution of organic N to total N fluxes, compared to soil extractions that generally are dominated by inorganic N (Brackin et al, 2015, Ganeteg et al, 2017, Inselsbacher and Näsholm, 2012a, Oyewole et al, 2016. The greater presence of organic N in fluxes is thought to be a product of the minimal disruption of the soil environment which reduces mineralisation and artificial solubilisation of N (Inselsbacher, 2014, Rousk andJones, 2010).…”

“…Previous work has highlighted the greater relative contribution of amino acids to microdialysis fluxes in comparison to extractions , Brackin et al, 2015, Oyewole et al, 2016, Ganeteg et al, 2017 suggesting that in many soils, amino acids are a dominant pool of available N to plants and microbes. We show that the major disparity between microdialysis and soil extractions mostly lies in the estimation of the contribution and timing of inorganic N, particularly during periods of high microbial activity and N turnover.…”

“…Diffusive fluxes have proven a useful measure of soil solute availability, particularly given they are measured in similar units to other relevant fluxes, such as solute uptake by roots (Brackin et al, 2015, Demand et al, 2017 and emissions of greenhouse gases from soil (Leitner et al, 2017b, Leitner et al, 2017a, and are commonly quoted in microdialysis soil studies (Inselsbacher et al, 2011, Shaw et al, 2014, Ganeteg et al, 2017. However, there are some considerations regarding the deployment and interpretation which may influence findings and make comparisons between studies challenging -but these influences could be minimised through standardisation of the technique.…”