Microbial amelioration of salinity stress in endangered accessions of Iranian licorice (Glycyrrhiza glabra L.)

Abstract

Background: Glycyrrhiza glabra L. is a medicinal and industrial plant that has gone extinct due to different abiotic stress caused by climate change. To understand how the plant-associated microorganism can support this plant under salinity, we collected sixteen Iranian accessions of G. glabra L., inoculated their rhizomes with Azotobacter sp. (two levels, bacterial treatments, and no-bacterial treatments, and grown them under salinity stress (NaCl levels; 0, and 200 mM).

Results: Two accessions of Bardsir and Bajgah significantly showed higher resistant to salinity, for example by increasing crown diameter (11.05 and 11 cm, respectively) compared to an average diameter of 9.5 in other accessions. Azotobacter inoculation caused a significant increase in plant height and crown diameter. Among studied accessions, Kashmar (46.21%) and Ilam (44.95%) had the highest rate of membrane stability index (MSI). Evaluation of enzyme activity represented that bacterial application under salinity, increased polyphenol oxidase (PPO) (0.21 U mg^-1 protein), peroxidase (POD) (3.09 U mg^-1 protein U mg^-1 protein), and phenylalanine ammonia-lyase (PAL) (17.85 U mg^-1 protein) activity. Darab accession showed the highest increase (6.45%) in antioxidant potential compared with all studied accessions under Azotobacter inoculation. According to principal component analysis (PCA), it was found that the accession of Meshkinshahr showed a more remarkable ability to activate its enzymatic defense system under salt stress. Also, three accessions of Meshkinshahr, Eghlid, and Ilam were categorized in separated clusters than other accessions regarding various studied treatments.

Conclusion: Analysis indicated that five accessions of Meshkinshahr, Rabt, Piranshahr, Bardsir, and Kermanshah from the perspective of induced systematic resistance are the accessions that showed a greater morphophysiological and biochemical outcome under salinity. This study suggested that, inoculation of with Azotobacter on selected accession can relieve salt stress and support industrial mass production under abiotic condition.

Keywords: Antioxidant Enzymes; Azotobacter; Licorice Population; Plant Growth-Promoting Rhizobacteria; Salt Stress.

Fig. 1

The collection areas for the investigated accessions of G. glabra

Fig. 2

Crown diameter variation of Iranian licorice under studied treatments. a crown diameter variation in different studied accessions b crown diameter variation under salinity stress. According to the analysis of variance that only the main effect of a accession and b salinity levels showed a significant difference on crown diameter, just their mean comparisons are shown. c According to the analysis of variance that double effects of Azotobacter and salinity levels showed a significant difference on plant height, the slice method was used for mean comparisons. Columns with the same letter are not significantly different (p ≤ 0.05) (Tukey test). Bars stand for standard error (SE)

Fig. 3

a Electrolyte leakage and b membrane stability index variation of Iranian licorice under salinity stress. According to the analysis of variance that double effects of accessions and salinity levels showed a significant difference, the slice method was used for mean comparisons. Columns with the same letter are not significantly different (p ≤ 0.05) (Tukey test). Bars stand for standard error (SE)

Fig. 4

The enzyme activity of Licorice under integrated salinity stress and Azotobacter application. a Polyphenol oxidase, b Peroxidase, and c Phenylalanine Ammonia-Lyase. According to the analysis of variance that double effects of Azotobacter and salinity levels showed a significant difference, the slice method was used for mean comparisons. Columns with the same letter are not significantly different (p ≤ 0.05) (Tukey test). Bars stand for standard error (SE)

Fig. 5

The Phenylalanine Ammonia-Lyase activity of Iranian Licorice accessions under Azotobacter application. According to the analysis of variance that double effects of Azotobacter and accession showed a significant difference, the slice method was used for mean comparisons. Columns with the same letter are not significantly different (p ≤ 0.05) (Tukey test). Bars stand for standard error (SE)

Fig. 6

PCA-Biplot for the investigation of Iranian licorice accessions under studied treatments. a A₀S₀ (control); b A₀S₁ (no-bacterial treatment × salinity); c A₁S₀ (bacterial treatment × no-salinity); d A₁S₁ (bacterial treatment × salinity). CAT (Catalase), SOD (Superoxide dismutase), APX (Ascorbate peroxidase), POD (Peroxidase), PPO (Polyphenol oxidase), PAL (Phenylalanine Ammonia-Lyase), MDA (Malondialdehyde), EL (electrolyte leakage) and MSI (Membrane stability index)

Fig. 7

Corrplot between various measured parameters of Iranian licorice accessions under studied treatments. a A₀S₀ (control); b A₀S₁ (no-bacterial treatment × salinity); c A₁S₀ (bacterial treatment × no-salinity); d A₁S₁ (bacterial treatment × salinity). CAT (Catalase), SOD (Superoxide dismutase), APX (Ascorbate peroxidase), POD (Peroxidase), PPO (Polyphenol oxidase), PAL (Phenylalanine Ammonia-Lyase), MDA (Malondialdehyde), EL (electrolyte leakage) and MSI (Membrane stability index)

Fig. 8

Cluster analysis of Iranian licorice accessions under studied treatments. a A₀S₀ (control); b A₀S₁ (no-bacterial treatment × salinity); c A₁S₀ (bacterial treatment × no-salinity); d A₁S₁ (bacterial treatment × salinity)