Role of Arbuscular Mycorrhizal (AM) Fungi on Growth, Cadmium Uptake, Osmolyte, and Phytochelatin Synthesis in Cajanus cajan (L.) Millsp. Under NaCl and Cd Stresses

Application of phosphatic (P) fertilizers and biosolids is known to enhance cadmium (Cd) contamination in saline soils. Increased concentration of dissolved chloride (Cl^?) in soil solution significantly influences Cd bioavailability in P fertilizer- or biosolid-amended soils. Arbuscular mycorrhizal (AM) fungi have an ability to protect plants against salinity and heavy metals by mediating interactions between toxic ions and plant roots. The effects of Glomus mosseae (AM) and NaCl and Cd stresses on Cd uptake and osmolyte and phytochelatin (PCs) synthesis in Cajanus cajan (L.) Millsp. (pigeonpea) were studied under greenhouse conditions. Two genotypes Sel 85?N (tolerant) and ICP 13997 (sensitive)] were subjected to NaCl (4 and 6?dS?m^?1) and Cd (CdCl₂, 25 and 50?mg?kg^?1 dry soil) treatments. NaCl and Cd applied individually as well as in combination caused dramatic reductions in plant biomass and induced membrane peroxidation, ionic perturbations, and metabolite synthesis in both genotypes, although Sel 85?N was less affected than ICP 13997. Cadmium uptake was enhanced when NaCl was added along with Cd. The protection of growth in Sel 85?N was associated with restricted accumulation of Na⁺, Cl^?, and Cd²⁺ and higher concentrations of stress metabolites (sugars, proteins, free amino acids, proline, glycine betaine). Cd led to a significant increase in biothiols (NP-SH) and glutathione (GSH), with a larger pool of NP-SH which strongly induced accumulation of phytochelatins, whereas no significant effects in their concentrations were detectable under NaCl stress. The interactive effects of NaCl and Cd on all parameters were larger than those of individual treatments. Fungal inoculations improved plant growth and reduced accumulation of toxic ions. Higher stress metabolite synthesis and PCs observed in AM plants of Sel 85?N indicated the role of an efficient AM symbiosis capable of attenuating NaCl and Cd stresses.