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<p>Drought stress was a critical environmental factor limiting plant growth, metabolism, and secondary metabolite production. Among these compounds, rosmarinic acid (RA) plays a key role due to its antioxidant and pharmaceutical properties, making its biosynthesis highly sensitive to water availability. Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) had been shown to enhance stress tolerance by modulating physiological, biochemical, and molecular responses. This study investigated the effects of AMF (<i>Funneliformis mosseae</i>) and PGPR (<i>Pseudomonas fluorescens</i> and <i>Azospirillum lipoferum</i>), both individually and in combination, on rosmarinic acid biosynthesis and molecular mechanisms in <i>M. officinalis</i> under drought stress (50% field capacity, FC) and optimal irrigation (100% FC). The results revealed that microbial inoculation significantly improved rosmarinic acid accumulation, particularly under drought conditions, with dual inoculation (<i>P. fluorescens</i> + <i>F. mosseae</i>) leading to an 8.08&#xa0;mg g⁻¹ DM increase in rosmarinic acid content 50.9% higher than non-inoculated plants. Furthermore, microbial treatments upregulated key genes involved in rosmarinic acid biosynthesis, including <i>PAL</i>, <i>4CL</i>, and <i>RAS</i>, with the highest expression levels observed in <i>P. fluorescens</i> + <i>F. mosseae</i> treated plants under water deficit conditions (<i>PAL</i>: 7.84-fold, <i>4CL</i>: 7.90-fold, <i>RAS</i>: 7.24-fold). Inoculation also enhanced antioxidant enzyme activities (superoxide dismutase, catalase, peroxidase) and reduced oxidative damage by lowering lipid peroxidation and hydrogen peroxide levels. These findings indicate that arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria synergistically enhance drought tolerance in <i>M. officinalis</i> by improving water status, increasing antioxidant defense, and upregulating molecular pathways involved in rosmarinic acid biosynthesis. This study highlighted the potential application of microbial inoculants as sustainable biofertilizers to enhance secondary metabolite production and stress resilience in medicinal plants.</p>

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Enhancing rosmarinic acid accumulation and drought tolerance in Melissa officinalis through arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria inoculation

  • 期刊论文

  • 发表日期：

    2026年2月17日

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  • Basoz Sadiq Muhealddin

摘要

Drought stress was a critical environmental factor limiting plant growth, metabolism, and secondary metabolite production. Among these compounds, rosmarinic acid (RA) plays a key role due to its antioxidant and pharmaceutical properties, making its biosynthesis highly sensitive to water availability. Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) had been shown to enhance stress tolerance by modulating physiological, biochemical, and molecular responses. This study investigated the effects of AMF (Funneliformis mosseae) and PGPR (Pseudomonas fluorescens and Azospirillum lipoferum), both individually and in combination, on rosmarinic acid biosynthesis and molecular mechanisms in M. officinalis under drought stress (50% field capacity, FC) and optimal irrigation (100% FC). The results revealed that microbial inoculation significantly improved rosmarinic acid accumulation, particularly under drought conditions, with dual inoculation (P. fluorescens + F. mosseae) leading to an 8.08 mg g⁻¹ DM increase in rosmarinic acid content 50.9% higher than non-inoculated plants. Furthermore, microbial treatments upregulated key genes involved in rosmarinic acid biosynthesis, including PAL, 4CL, and RAS, with the highest expression levels observed in P. fluorescens + F. mosseae treated plants under water deficit conditions (PAL: 7.84-fold, 4CL: 7.90-fold, RAS: 7.24-fold). Inoculation also enhanced antioxidant enzyme activities (superoxide dismutase, catalase, peroxidase) and reduced oxidative damage by lowering lipid peroxidation and hydrogen peroxide levels. These findings indicate that arbuscular mycorrhizal fungi and plant growth-promoting rhizobacteria synergistically enhance drought tolerance in M. officinalis by improving water status, increasing antioxidant defense, and upregulating molecular pathways involved in rosmarinic acid biosynthesis. This study highlighted the potential application of microbial inoculants as sustainable biofertilizers to enhance secondary metabolite production and stress resilience in medicinal plants.