Effects of Poly-γ-Glutamic Acid (γ-PGA) on Metabolites of Flue-Cured Tobacco Leaves Based on Metabolomics Analysis

Poly-γ-glutamic acid(γ-PGA) is a water-soluble polyamino acid produced by microbial fermentation, which can be used as plant growth regulator and has great agricultural application prospects. To determine the effect of γ-PGA application on the metabolic substances in flue-cured tobacco leaves, the samples of tobacco leaves with and without γ-PGA application were collected, and the non-targeted metabolomics analysis was performed using liquid chromatography-mass spectrometry (LC-MS/MS). Compared with the control, 14 metabolites with substantial differences were detected in flue-cured tobacco leaves after γ-PGA application. Eight metabolites, mainly classified as organoheterocyclic compounds, were up-regulated and 6 metabolites, mainly classified as organic oxygenates, were down-regulated. The differential metabolites were enriched in multiple metabolic pathways, such as the biosynthesis of amino acids, mineral absorption, protein digestion and absorption, and carbon metabolism. The main enriched differential metabolites were proline, tryptophan, 3-Methyl-2-oxobutanoic acid, fumaric acid, and d-glucose. Therefore, γ-PGA application can affect the accumulation and transformation of carbon and nitrogen compounds in tobacco leaves, and regulate the process of carbon and nitrogen metabolism in tobacco leaf growth.