Monitoring amino acid profile and protein quality of Licorice (Glycyrrhiza glabra L.) under drought stress, silicon nutrition and mycorrhiza inoculation

Abiotic stresses usually trigger plant responses that entail several changes in the metabolism of amino acids. The Glycyrrhiza glabra rhizomes activate integrative biochemical networks in response to water deficit conditions, mycorrhiza inoculation, and silicon application. In the present study, irrigation was performed to make the soil reach 5 different levels of 20, 40, 60, 80, and 100% of field capacity (control). Silicon application was used at 300 ppm concentration solute in irrigation water for half of treatments. The Claroiedoglomus etunicatum is used as mycorrhizal inoculum. After 2 months, the amino acid profile of treated plants (from acidic root extracts) was analyzed by Liquid Chromatography–tandem mass spectrometry (LC-MS/MS). Results were indicated that amino acids changed as a result of water deficiency, silicon nutrition, and mycorrhiza inoculation. As proline accumulation can be one of the indicator responses to drought stress, in this study, 100% irrigation with applying silicon, without mycorrhiza inoculation showed increased levels in proline (83.09 mg.g⁻¹ dry biomass), while minimum proline (18.27 mg.g⁻¹ dry biomass) was observed by 40% irrigation with mycorrhiza inoculation, without applying silicon. Maximum values of histidine (23.19 mg.g⁻¹ dry biomass) and lysine (36.29 mg.g⁻¹ dry biomass) were observed by application of 80% field capacity water irrigation with silicon solution and fungi inoculation. Minimum histidine and valine were in the treatment of 100% field capacity irrigation without silicon and inoculation (3.15 and 6.64 mg.g⁻¹ dry biomass, respectively). As minimum amino acids were almost observed in treatments that were not achieved silicon and mycorrhiza, so results of this study showed that silicon at 300 ppm and licorice root inoculation by C. etunicatum effectively can change amino acid profile and protein quality under drought stress. Comprehensive results were achieved with a detailed understanding of how drought stress can trigger plant responses via relevant mechanisms, therefore enabling the use of mineral nutrition, such as silicon, and biofertilizers, including mycorrhiza, in crop enhancements.