Arbuscular Mycorrhizae Impart Cd Tolerance in Cajans Cajan (L.) Millsp. by Upregulating the Expression of Metallothionein (CcMT1) and Phytochelatin Synthase (CcPCS1) Genes

Cadmium pollution of soil restricts growth and yield of crop plants. Arbuscular mycorrhizae play significant roles in imparting tolerance to Cd toxicity by establishing symbiotic association with the host plants species. The present study therefore evaluated the effects of four arbuscular mycorrhizal fungal species (AMF), i.e. Claroideoglomus claroideum (AM1), Claroideoglomus etunicatum (AM2), Funneliformis mosseae (AM3) and Rhizoglomus intraradices (AM4), in modulating physiological and molecular attributes of Cd-stressed (Cd - 0, 50 mg/kg) Cajanus cajan (L.) Millsp. (pigeon pea) plants. Application of Cd reduced growth (more in roots than shoots), nitrogen fixing potential and yield. It also led to generation of reactive oxygen species as well as membrane leakiness. AMF supplementations improved growth, nutrient acquisition, rhizobial symbiosis, reduced oxidative burden and Cd uptake by enhancing the synthesis of thiols (cysteine, reduced and oxidized glutathione, phytochelatins, non-protein thiols). Activity of glutathione reductase increased significantly in AMF inoculated plants which imparted redox balance by improving GSH/GSSG ratio in roots and shoots. Quantitative RT-PCR analysis displayed abundance of transcripts encoding two metal chelator genes; metallothionein (CcMT1) and phytochelatin synthase1 (isoforms CcPCS1X1, CcPCS1X2 and CcPCS1X4) which expressed more in roots than leaves of Cd-stressed AMF plants. Moreover, expression level of CcMT1 was more intense than CcPCS1 indicating higher ability of MTs to combat Cd stress than PCS. R. intraradices was the most efficient in inducing the expression of metal responsive genes than other three species suggesting its promising role in the amelioration of Cd toxicity in pigeon pea.