Glomalin production by Rhizophagus irregularis in vitro condition and pot culture of white clover and its role in Pb-sequestration

Glomalin as a glycoprotein produced by mycorrhizal fungi plays important role in sequestration of heavy metals in soils. Two experiments (pot and in vitro cultures) were conducted according to this hypothesis that heavy metals stress could increase glomalin production and metal complexes. Glomalin Bradford reactive extracted from hyphal compartment and the amounts of Pb-sequestrated by glomalin were investigated both in pot and in vitro cultures. Pot experiment was studied in washed sands using clover plant colonized by Rhizophagus irregularis fungus and treated with 0, 150, 300 and 450 µM of Pb. In vitro experiment was performed in two-compartments plates containing carrot roots colonized by the same fungus and treated with 0, 0.01, 0.1 and 1 mM of Pb as Pb(NO3)2. There was no significant correlation between mycorrhizal parameters including dry weight of fungus mycelium and percentage of hyphal frequency with content of glomalin extracted from hyphal compartment of pot and in vitro cultures, respectively. Glomalin contents extracted from hyphal compartment of pot and in vitro cultures were significantly improved by increasing Pb concentration compared to the control treatment. Pb-sequestrated by glomalin significantly increased as Pb concentrations and glomalin production increased. There was positive and significant correlation between Bradford reactive hyphal glomalin with Pb-sequestrated by glomalin. The results of this study revealed that the glomalin plays important role in Pb sequestration and thereby makes it valuable in phytostabilization of Pb in polluted soils.