The Role of Funneliformis mosseae Symbiosis on Cotton Plants under Lead Toxicity: Molecular and Physiological Aspects

Arbuscular mycorrhizal fungi can impact the host’s response to various environmental challenges, including lead (Pb) stress. Consequently, an investigation was set up to evaluate how the inoculation of Funneliformis mosseae (F. mosseae; FM) impacts the defense mechanisms in cotton plants subjected to Pb (1000 mg/kg) stress. The Pb treatment resulted in a substantial rise in Pb accumulation in both the roots and leaves. This led to elevated levels of methylglyoxal and hydrogen peroxide in the cotton leaves, accompanied by an increase in malondialdehyde content, ion leakage, and a reduction in photosynthetic pigments. The alterations were linked to a decline in photosynthetic performance and overall plant growth. Nevertheless, inoculation with the F. mosseae fungus resulted in the enhancement of photosynthetic pigment contents and the upregulation of Rubisco S and Rubisco L subunits, contributing to the protection of photosynthetic processes in stressed plants. Furthermore, this symbiotic fungus, through reducing Pb absorption and inducing increased activity of antioxidant and glyoxalase enzymes, led to the reduction of hydrogen peroxide and methylglyoxal levels while safeguarding membrane integrity under Pb stress. Plants inoculated with F. mosseae exhibited higher levels of metal-sequestering organic compounds, including glutathione and phytochelatins, in both roots and leaves, indicating their protective role in sequestering Pb from leaf tissues against Pb toxicity. This symbiosis also made photosynthetic organs more resistant to Pb toxicity by changing the metabolism of polyamines and making more spermidine and spermine levels in the leaves. Our research provides a theoretical foundation for the remediation of the symbiotic relationship between F. mosseae and cotton in environments contaminated with lead.