Harnessing the role of arbuscular mycorrhizae in arresting nodular senescence by modulating osmolyte synthesis and ascorbate-glutathione pool in cadmium stressed pigeon pea

Contamination of soil with cadmium (Cd) is a severe environmental problem, worldwide. Different arbuscular mycorrhizal fungal (AMF) species with suitable host plant combinations plays a crucial role in alleviating the impact of metal toxicity. The present study investigated the relative effects of AMF species: Claroideoglomus claroideum (M1), Claroideoglomus etunicatum (M2), Funneliformis mosseae (M3), Rhizoglomus intraradices (M4), in imparting tolerance to Cajanus cajan (L.) Millsp. - (Pigeon pea) under Cd (0, 25, 50 mg/kg) stress. The Cd had a negative impact on plant growth, nitrogen fixing efficacy, trehalose metabolism and nutrient acquisition in the nodules. The AMF supplementations improved the functional efficiency of nodules by enhancing nutrient uptake and reducing Cd absorption in plants. The mycorrhizations accelerated the synthesis of osmolytes such as trehalose (Tre), total protein (TP), total soluble sugars (TSS), total free amino acids (TFAA) and proline, responsible for maintaining the osmotic balance, otherwise disturbed in Cd-stressed pigeon pea. Furthermore, mycorrhizal inoculations upregulated the activity of enzymes involved in the ascorbate and glutathione cycle impending redox homeostasis by enhancing the ratios of ascorbate/dehydroascorbate and reduced glutathione/oxidised glutathione [ASA/DHA and GSH/GSSG]. However, among the four AMF species, M4 was the most beneficial in improving the nodulation potential and nutrient acquisition, followed by M3 and M2 (almost equally competent), with the least positive impact of M1. The differential abilities of four AMF species could be associated with their differential responsiveness to improve root biomass responsible for establishing an effective microbial symbiosis (mycorrhizal and rhizobial) and restricting metal uptake. Overall, the study suggested selecting the most efficient AMF species that provide functional complementarity to symbiosomes for inducing Cd tolerance in pigeon pea plants.

Automated summary

This study investigated the relative effects of four arbuscular mycorrhizal fungal (AMF) species on pigeon pea plants under cadmium stress. The results showed that Rhizoglomus intraradices (M4) had the greatest positive impact on nodulation potential and nutrient acquisition, followed by Funneliformis mosseae (M3) and Claroideoglomus etunicatum (M2), while Claroideoglomus claroideum (M1) had the least positive impact. Therefore, selecting the most efficient AMF species is recommended to improve cadmium tolerance in pigeon pea plants.