Dark septate endophytic fungus Alternaria sp. 17463 regulates various antioxidant enzymes and compounds to mitigate salt stress caused by different anion salts.

In the field of agricultural and environmental management, understanding how dark septate endophytic fungi (DSE) like Alternaria sp. 17463 respond to salt stress is crucial. Prior research has yet to fully explore the anion-specific responses of DSE to salt stress. In this study, we delve into the physiological and biochemical responses of Alternaria sp. 17463 under NaCl and Na₂SO₄ stress, employing a suite of analytical techniques. We discovered a marked disparity in fungal tolerance, with NaCl inducing a 50 % growth reduction at 0.6 M and a complete growth arrest at 1.4 M, contrasting with Na₂SO₄'s milder 30 % impact at the highest tested concentration. Cell membrane integrity was severely compromised under NaCl, with a 70 % increase in permeability and a 40 % plummet in cell viability at 1.4 M, whereas Na₂SO₄ induced only a 20 % permeability increase. Antioxidant enzyme profiling revealed a twofold surge in superoxide dismutase (SOD) activity under NaCl at 0.4 M, and a 1.5-fold rise in catalase (CAT) activity under Na₂SO₄. Furthermore, there was a significant correlation between Na⁺ concentration and cellular responses, particularly under Na₂SO₄ stress, where higher sodium tolerance was linked to enhanced melanin, reduced glutathione (GSH), and total glutathione (tGSH) levels. Our findings not only illuminate the nuanced response of Alternaria sp. 17463 to anionic stress but also underscore the fungus's potential as a bioindicator for salt stress. This research paves the way for developing targeted microbial interventions to bolster crop performance in saline environments, offering a significant step forward in precision agriculture.