Effects of humic substances and indole-3-acetic acid on Arabidopsis sugar and amino acid metabolic profile

Abstract

Humic substances (HS) are known to influence plant physiological processes, enhancing crop yield, plant growth and nutrient uptake. The present study sought to gain a better understanding of the specific effects of HS application on the abundance of metabolites in plant tissues, using mass spectrometry analyses. Arabidopsis thaliana plants, grown in hydroponic conditions, were treated for 8 h with indole-3-acetic acid (IAA), HS from International Humic Substances Society (IHSS) and HS from earthworm faeces (EF), respectively. Humic substances structural characteristics were analyzed by 1H NMR an FT-IR spectroscopies. Root and leaf free amino acids, sugar alcohols and carbohydrate contents, and leaf amino acids from protein hydrolysis were identified and quantified by gas chromatography-mass spectrometry (GC/MS), and liquid chromatography-mass spectrometry (LC/MS). Canonical discriminant analysis (CDA) was used to evaluate the influence of the treatments on the studied parameters. EF treatment had the highest influence on metabolite profiles compared to the control, IAA and IHSS. CDA analysis highlighted a clear distinction between EF and IHSS plant physiological responses, depending on the different chemical and structural properties of the HS. IAA-treated plants showed no significant difference from the control. A better understanding of the specific effects of different HS, also related to their chemical characteristics, might serve as a basis for the identification of marker compounds for HS bioactivity.