Plant growth promoting endophytic fungus Aspergillus niger VN2 enhances growth, regulates oxidative stress and protects DNA damage in Vigna radiata under salt stress.

Abstract

Background: Plant microbe-interactions contribute in mitigating abiotic environmental stresses in plants. Salinity stress is one of major factor in reducing agricultural productivity. Recently, the use of endophytic fungi has proved as one of the approaches that can help plant growth under salt stress. Therefore, the objective of this study was to isolate halotolerant endophytic fungi and elevate their potential to mitigate salt stress in Vigna radiata.

Methodology: Endophytic fungi were isolated from asymptomatic parts of Vachellia nilotica and screened for plant growth-promoting attributes such as IAA production, phosphate solubilization, siderophore production, and halotolerance. Based on growth-promoting characteristics and halotolerance, Aspergillus niger VN2 was selected and colonized in V. radiata. The colonized plants were exposed to different salt concentrations (150 mM, 200 mM, and 250 mM NaCl) to evaluate the effect of A. niger VN2 in mitigating salt stress. The effects of A. niger VN2 colonization on physiological, biochemical, and molecular parameters were assessed.

Results: In the present study, an endophytic fungus Aspergillus niger VN2 isolated from Vachellia nilotica exhibited good plant growth promotion properties and halotolerance. A. niger VN2 produced IAA (148.32 ± 2.34 µg/ml IAA), solubilized phosphate, and produced hydroxamate type siderophore (72.66% SU). It also exhibited ACC deaminase ability (134.40 ± 5.45µmolα-ketobutyrate/h/mg protein), and could tolerate up to 15% NaCl. Colonization of A. niger VN2 in V. radiata enhanced salt tolerance, and resulted in increased root and shoot length, biomass, leaf number, chlorophyll content, relative water content, and protein content in salt stressed plants. DPPH scavenging and endogenous IAA levels also increased in treated plants. Oxidative stress parameters viz. proline, electrolyte leakage, and malondialdehyde, were found to decrease in VN2 colonized plants. Fluorescent microscopy studies revealed VN2 colonized plants showed increased cell survival and lowered glutathione and hydrogen peroxide under salt stress. Comet assay was used for determining the genoprotective effect of A. niger VN2. Colonization of A. niger VN2 reduced DNA tail length, % tail DNA, tail moment, and olive tail moment in plants exposed to salt stress. The difference in biochemical molecules viz. protein, carbohydrates, lipid, and nucleic acid in colonized and non-colonized plants under salt stress was revealed by FT-IR spectroscopy and validated by PCA, which showed that A. niger VN2 mitigated salt-induced changes, as colonized samples clustered closely under both conditions.

Conclusion: From the current study, it can be concluded that colonization of endophytic fungus A. niger VN2 promotes plant growth and can mitigate salt stress in V. radiata by regulating oxidative stress.