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<p>Salinity stress is a major abiotic constraint that severely limits mung bean (Vigna radiata L.) productivity. In this study, the effects of two psychrotrophic plant growth-promoting rhizobacteria (<i>Lysinibacillus fusiformis</i> and <i>Lysinibacillus sphaericus</i>) were evaluated and compared with the exogenous application of osmoprotectants (proline and glycine betaine) under 150 mM NaCl stress. Out of 28 bacterial isolates obtained from the rhizosphere of <i>Suaeda nudiflora</i>, ten salt-tolerant isolates were selected based on plant growth-promoting traits, and the best-performing isolates (7 and 10) were identified as <i>L. fusiformis</i> (HM756642) and <i>L. sphaericus</i> (HM756643). Both bacterial strains significantly enhanced germination parameters, with improvements in germination percentage, index, and speed of emergence by up to 65–78% compared with the saline control, whereas osmoprotectants showed relatively lower enhancement (35–55%). Under salinity stress, bacterial inoculation improved plant growth traits by 70–80%, while proline and glycine betaine increased growth by 60–70%. Photosynthetic pigments increased significantly, with chlorophyll content enhanced by 40–60% in bacterial treatments compared to salt-stressed plants, along with a 30–50% improvement in net photosynthetic rate. Antioxidant enzyme activities showed marked induction, where superoxide dismutase (SOD) increased by 39–43% under normal conditions and was further elevated under salinity stress, while ascorbate peroxidase (APX) activity increased by up to 2.5-fold compared to control. Bacterial inoculation and osmoprotectants significantly improved relative water content (15–18% increase) and membrane stability index (up to 20% improvement), while reducing lipid peroxidation by approximately 35–45% under salinity stress. Mineral analysis revealed a substantial reduction in Na⁺ accumulation and a 40–60% improvement in the K⁺/Na⁺ ratio in bacterial-treated plants. Transcriptomic analysis showed that L. fusiformis induced the highest number of upregulated stress-responsive genes, including NHX1, HKT1, P5CS1, BADH, APX, SOD, and WRKY transcription factors, indicating strong activation of ion homeostasis, osmolyte biosynthesis, and antioxidant pathways. RNA-seq results were strongly validated by qRT-PCR (R² = 0.86). Overall, psychrotrophic <i>Lysinibacillus</i> strains were more effective than osmoprotectants in enhancing salinity tolerance through physiological, biochemical, and molecular regulation, demonstrating their potential as sustainable bioinoculants for saline agriculture.</p>

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Modulation of Mineral Homeostasis and Photosynthetic Performance in Mung Bean (Vigna radiata L.) by Psychrotrophic Bacteria and Osmoprotectants under Salinity Stress

  • 期刊论文

  • 发表日期：

    2026年7月7日

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  • Yachana Jha,
  • Heba I. Mohamed,
  • Haiam O. Elkatry,
  • Abdelrahman R. Ahmed

摘要

Salinity stress is a major abiotic constraint that severely limits mung bean (Vigna radiata L.) productivity. In this study, the effects of two psychrotrophic plant growth-promoting rhizobacteria (Lysinibacillus fusiformis and Lysinibacillus sphaericus) were evaluated and compared with the exogenous application of osmoprotectants (proline and glycine betaine) under 150 mM NaCl stress. Out of 28 bacterial isolates obtained from the rhizosphere of Suaeda nudiflora, ten salt-tolerant isolates were selected based on plant growth-promoting traits, and the best-performing isolates (7 and 10) were identified as L. fusiformis (HM756642) and L. sphaericus (HM756643). Both bacterial strains significantly enhanced germination parameters, with improvements in germination percentage, index, and speed of emergence by up to 65–78% compared with the saline control, whereas osmoprotectants showed relatively lower enhancement (35–55%). Under salinity stress, bacterial inoculation improved plant growth traits by 70–80%, while proline and glycine betaine increased growth by 60–70%. Photosynthetic pigments increased significantly, with chlorophyll content enhanced by 40–60% in bacterial treatments compared to salt-stressed plants, along with a 30–50% improvement in net photosynthetic rate. Antioxidant enzyme activities showed marked induction, where superoxide dismutase (SOD) increased by 39–43% under normal conditions and was further elevated under salinity stress, while ascorbate peroxidase (APX) activity increased by up to 2.5-fold compared to control. Bacterial inoculation and osmoprotectants significantly improved relative water content (15–18% increase) and membrane stability index (up to 20% improvement), while reducing lipid peroxidation by approximately 35–45% under salinity stress. Mineral analysis revealed a substantial reduction in Na⁺ accumulation and a 40–60% improvement in the K⁺/Na⁺ ratio in bacterial-treated plants. Transcriptomic analysis showed that L. fusiformis induced the highest number of upregulated stress-responsive genes, including NHX1, HKT1, P5CS1, BADH, APX, SOD, and WRKY transcription factors, indicating strong activation of ion homeostasis, osmolyte biosynthesis, and antioxidant pathways. RNA-seq results were strongly validated by qRT-PCR (R² = 0.86). Overall, psychrotrophic Lysinibacillus strains were more effective than osmoprotectants in enhancing salinity tolerance through physiological, biochemical, and molecular regulation, demonstrating their potential as sustainable bioinoculants for saline agriculture.