Abstract
Iron is an essential plant micronutrient. It is a component of numerous proteins and participates in cell redox reactions; iron deficiency results in a reduction in nutritional quality and crop yields. Volatiles from the rhizobacterium Arthrobacter agilis UMCV2 induce iron acquisition mechanisms in plants. However, it is not known whether microbial volatiles modulate other metabolic plant stress responses to reduce the negative effect of iron deficiency. Mass spectrometry has great potential to analyze metabolite alterations in plants exposed to biotic and abiotic factors. Direct liquid introduction-electrospray-mass spectrometry was used to study the metabolite profile in Medicago truncatula due to iron deficiency, and in response to microbial volatiles. The putatively identified compounds belonged to different classes, including pigments, terpenes, flavonoids, and brassinosteroids, which have been associated with defense responses against abiotic stress. Notably, the levels of these compounds increased in the presence of the rhizobacterium. In particular, the analysis of brassinolide by gas chromatography in tandem with mass spectrometry showed that the phytohormone increased ten times in plants grown under iron-deficient growth conditions and exposed to microbial volatiles. In this mass spectrometry-based study, we provide new evidence on the role of A. agilis UMCV2 in the modulation of certain compounds involved in stress tolerance in M. truncatula.
Highlights
Mass spectrometry (MS) is gaining considerable popularity for profiling metabolites in complex biological samples
High analytical performance allows it to be used for untargeted metabolomics screening approaches for different plant extracts; it offers an excellent cost-benefit ratio compared to other analytical platforms such as near-infrared reflectance spectroscopy (NIRS), ultra-performance liquid chromatography-mass spectrometry (UPLC-MS), gas chromatography with flame ionization detection (GC-FID), and GC-MS, which are slow and expensive to use for routine plant biochemistry studies [2]
We focused on the detection of significant differences among MS profiles to determine whether volatiles emitted by A. agilis UMCV2 alleviate plant stress and stimulate the accumulation of metabolites involved in abiotic stress tolerance; in addition, we used a complementary GC-MS method to confirm the identification of brassinolide, which is involved in Fe-adaptive processes in plants
Summary
Mass spectrometry (MS) is gaining considerable popularity for profiling metabolites in complex biological samples. Direct liquid introduction-electrospray ionization-mass spectrometry (DLI-ESI-MS, the acronym recommended by the Analytical Methods Committee [1]) is a rapid and high-throughput analytical tool that has been successfully applied in medicine and food and biological sciences [2,3,4,5]. High analytical performance (sensitivity, selectivity) allows it to be used for untargeted metabolomics screening approaches for different plant extracts; it offers an excellent cost-benefit ratio compared to other analytical platforms such as near-infrared reflectance spectroscopy (NIRS), ultra-performance liquid chromatography-mass spectrometry (UPLC-MS), gas chromatography with flame ionization detection (GC-FID), and GC-MS, which are slow and expensive to use for routine plant biochemistry studies [2]. Due to the various benefits reported for DLI-ESI-MS, we decided to conduct a study to determine its usefulness in microbial ecology research, as DLI-ESI-MS provides robust chemical information, is bioinformatically easy to handle, and could help us understand the chemical response of plants to abiotic or biotic factors
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