Evolution of the amino acid fingerprint in the unsterilized rhizosphere of a legume in relation to plant maturity

Abstract

The exudation of low-molecular-weight compounds, such as amino acids, contributes to the structure of rhizospheric microbial communities and plays a crucial role in nutrient mobility throughout the vegetative cycle of the plant. Due to their low concentration and their constant removal by microorganisms, the study of amino acids is difficult in unsterilized rhizospheric soil. Our aim was to investigate the dynamics of amino acids in unsterilized soil. Since there was currently no available method to estimate accurately amino acid exudation in soil, a methodology was developed to assess amino-acid fingerprints in the rhizosphere. This proved a viable approach for understanding the dynamics of amino-acid release into the rhizosphere. The method was tested on Medicago truncatula, with the hypothesis that the fingerprint of amino acids in the rhizosphere should reflects amino acid exudation from leguminous plants, subject to the influence of microbiological components of the soil, and should be correlated with the stage of plant growth. M. truncatula plants were grown in either unsterilized or sterilized substrate. Amino acids in the substrate samples were identified and quantified by gas chromatography-mass spectrometry (GC-MS) and microbial biomass in the soil samples was also assessed. The total content of amino acids in the sterilized rhizospheric substrate increased substantially during plant growth with the highest content observed at the end of the vegetative stage. Despite the probable continual removal of amino acids by microorganisms, we also observed a significant quantitative and qualitative plant-dependent effect on the amino acid fingerprint in unsterilized soil. A clear chronological differentiation of this fingerprint in the rhizosphere of unsterilized and sterilized substrate was revealed by principal component analysis. We observed predominantly serine and glycine in the sterilized rhizosphere, whereas asparagine became prominent before flowering in the unsterilized rhizosphere soil. Root amino acid metabolic pathways and exudation appear to differ in unsterilized soil compared to in sterilized substrate, indicating an adaption to the rhizospheric environment. The established method could be used in other applications, for example, for future ecophysiological studies aiming at following root exudation of amino acids in response to changing environmental conditions

Arabidopsis seedlings display a remarkable resilience under severe mineral starvation using their metabolic plasticity to remain self‐sufficient for weeks

“…Analyses were carried out according to Bobille et al . (), except for the elution profile: 70°C for 5 min, linear gradient of 5°C min −1 to 300°C, 300°C for 5 min, resulting in a total run time of 56 min. For the detection of sugars, samples were diluted 1:80 and analysed by HPLC at 30°C with 10% (m/v) NaOH on a Carbopac PA‐1 column (Dionex Corp., Sunnyvale, CA, USA) using pulsed amperometric detection, as described by Tetteroo et al .…”

Absence of 4-Formylaminooxyvinylglycine Production by Pseudomonas fluorescens WH6 Results in Resource Reallocation from Secondary Metabolite Production to Rhizocompetence

“…How these amino acids might regulate FVG production and the significance of decreasing production of FVG in their presence is unknown. However, acidic amino acids and their amides may modulate FVG expression in the rhizosphere as they are exuded by roots [48,49]. Further, it has been shown that microbial products can enhance efflux of amino acids from roots [50].…”

“…Our differential expression data indicate that ∆gvgR, A, and C strains have increased transcription of genes necessary for motility and chemotaxis and phenotypic analysis shows these mutants are more motile. In addition, in the presence of glutamate, an amino acid shown to be abundant in some root exudates [48,49], motility of WT WH6 increases while production of FVG decreases. This suggests a tradeoff between FVG production and increased capacity for rhizosphere colonization.…”

Asparagine and sugars are both required to sustain secondary axis elongation after bud outgrowth in Rosa hybrida

“…Amino acid concentrations in the sap exudates were determined by gas chromatography-mass spectrometry (GC-MS). Extraction of 10 μL or 50 μL and purification of amino acids on cation-exchange column (DOWEX 50W-X8) and their quantification with a 436-GC coupled to a simple quadruple SCION MS (Bruker), were carried out according to Bobille et al (2016).…”