Cd-induced production of glomalin by arbuscular mycorrhizal fungus (Rhizophagus irregularis) as estimated by monoclonal antibody assay.

Glomalin is a specific fungal glycoprotein produced by arbuscular mycorrhizal (AM) fungi belonging to the Glomerales which could efficiently sequestrate heavy metals. The glomalin has been introduced as a heat shock protein and there are evidences that increasing levels of heavy metals could enhance its production. We examined the influence of Cd concentrations on glomalin production by AM fungus, as well as its contribution to the sequestration of Cd in both pot and in vitro culture conditions. Pot experiment was carried out using pure sand with Trifolium repens L. as host plant, mycorrhized by Rhizophagus irregularis and treated with Cd levels of 0, 15, 30, and 45 μM. In vitro experiment was performed in two-compartment plates containing the transformed carrot roots mycorrhized with the same fungus and treated with Cd levels of 0, 0.001, 0.01, and 0.1 mM. The immunoreactive and Bradford reactive glomalin contents in both experiments increased as so raising Cd concentration. Total Cd sequestrated by hyphal glomalin in both cultures was significantly increased as the levels of Cd increased. The highest contents of Cd sequestration in pot (75.78 μg Cd/mg glomalin) and in vitro (11.44 μg Cd/mg glomalin) cultures were recorded at the uppermost levels of Cd, which significantly differed with other levels. Our results suggested that under Cd-induced stress, stimulated production of glomalin by AM fungus may be a protective mechanism against the toxic effect of Cd.