Purpose Glomalin as a specific glycoprotein is produced by the fungi belong to the phylum Glomeromycota. There are evidences indicating that glomalin plays a major role in stabilization of potentially toxic elements (PTEs) in soils by making them less available to plant roots. However, PTEs could negatively affect root colonization and glomalin secretion by the fungi. Glomalin production may be induced under stressful conditions. Materials and methods In this study, three levels of Pb including 0, 500 and 1000 mg Pb.kg−1 soil (Pb0, Pb1 and Pb2, respectively) as lead nitrate were added to the soil. Sunflower (Helianthus annuus L. cv. Farrokh Hybrid) seeds were sown in pots containing sterilized soil and inoculated with Rhizophagus irregularis or left un-inoculated as control. Root colonization percentage, glomalin content in root (RG) and soil (SG), and the amount of Pb immobilized by RG and SG were determined. Results and discussion The results showed that mycorrhizal root colonization caused a significant increase in the RG and SG. Higher Pb levels significantly reduced both SG and RG (p < 0.05). Compared to the Pb0 control, soil glomalin (SG) was reduced by 23.3% at Pb1 and 33.4% at Pb2, while RG was reduced by 28.9% and 38.8%, respectively. The amounts of Pb immobilized by SG at Pb1 and Pb2 levels were 3.433 and 4.755 mg g−1 in mycorrhizal, and 2.984 and 3.983 mg g−1 in non-mycorrhizal treatments, respectively. However, the amount of SG per unit of root colonization as an index, decreased at both Pb1 and Pb2 levels compared to the Pb0 but a significant (p < 0.01) increase (85.5%) was seen by elevating Pb level from Pb1 to Pb2. It seems that although the glomalin production by fungal organs is inhibited at both Pb1 and Pb2 levels but the fungus is induced to secret more glomalin per unit of root colonization at Pb2 compared to Pb1. This might be a mechanism to protect the fungus against Pb toxicity. Conclusions Root colonization by the fungus was negatively affected by enhancing Pb concentration in soil which caused a decline in glomalin production both in soil (SG) and root (RG). However, a noticeable phenomenon was seen in the amount of SG per unit of root colonization. This index was significantly higher at Pb2 than Pb1, indicating the stimulation of glomalin production by the fungus at higher level of toxicant.

Pb-stress-mediated secretion of glomalin by Rhizophagus irregularis fungus associated with sunflower roots

期刊论文
发表日期：

2026年4月10日

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Amir Hossein Daneshfar,
Nasser Aliasgharzad,
Shahin Oustan

摘要

Purpose

Glomalin as a specific glycoprotein is produced by the fungi belong to the phylum Glomeromycota. There are evidences indicating that glomalin plays a major role in stabilization of potentially toxic elements (PTEs) in soils by making them less available to plant roots. However, PTEs could negatively affect root colonization and glomalin secretion by the fungi. Glomalin production may be induced under stressful conditions.

Materials and methods

In this study, three levels of Pb including 0, 500 and 1000 mg Pb.kg⁻¹ soil (Pb₀, Pb₁ and Pb₂, respectively) as lead nitrate were added to the soil. Sunflower (Helianthus annuus L. cv. Farrokh Hybrid) seeds were sown in pots containing sterilized soil and inoculated with Rhizophagus irregularis or left un-inoculated as control. Root colonization percentage, glomalin content in root (RG) and soil (SG), and the amount of Pb immobilized by RG and SG were determined.

Results and discussion

The results showed that mycorrhizal root colonization caused a significant increase in the RG and SG. Higher Pb levels significantly reduced both SG and RG (p < 0.05). Compared to the Pb₀ control, soil glomalin (SG) was reduced by 23.3% at Pb₁ and 33.4% at Pb₂, while RG was reduced by 28.9% and 38.8%, respectively. The amounts of Pb immobilized by SG at Pb₁ and Pb₂ levels were 3.433 and 4.755 mg g⁻¹ in mycorrhizal, and 2.984 and 3.983 mg g⁻¹ in non-mycorrhizal treatments, respectively. However, the amount of SG per unit of root colonization as an index, decreased at both Pb₁ and Pb₂ levels compared to the Pb₀ but a significant (p < 0.01) increase (85.5%) was seen by elevating Pb level from Pb₁ to Pb₂. It seems that although the glomalin production by fungal organs is inhibited at both Pb₁ and Pb₂ levels but the fungus is induced to secret more glomalin per unit of root colonization at Pb₂ compared to Pb₁. This might be a mechanism to protect the fungus against Pb toxicity.

Conclusions

Root colonization by the fungus was negatively affected by enhancing Pb concentration in soil which caused a decline in glomalin production both in soil (SG) and root (RG). However, a noticeable phenomenon was seen in the amount of SG per unit of root colonization. This index was significantly higher at Pb₂ than Pb_1, indicating the stimulation of glomalin production by the fungus at higher level of toxicant.