RESEARCH ARTICLE Relative effectiveness of arbuscular mycorrhiza and polyamines in modulating ROS generation and ascorbate-glutathione cycle in Cajanus cajan under nickel stress Kiran Saroy 1 & Neera Garg 1 Received: 6 January 2021 /Accepted: 6 April 2021 # The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2021 Abstract Nickel (Ni) is a fundamental micronutrient in plants but hampers plant growth and metabolism at elevated levels in the soil by inducing oxidative stress. In the recent years, use of polyamines (PAs) and arbuscular mycorrhiza (AM) have gained importance for their roles in enabling plants to withstand Ni toxicity. However, information about their comparative effectiveness in alleviating Ni stress is scanty. Therefore, the current study was designed to evaluate relative impacts of three PAs (Put, Spd, and Spm) and AM (Rhizoglomus intraradices) in reducing Ni uptake, ROS generation, and modulating antioxidant defense machinery in two pigeonpea genotypes (Pusa 2001-tolerant and AL 201-sensitive). Roots of Ni supplied plants accumulated significantly more Ni than the leaves, more in AL 201 than Pusa 2001, which was proportionate to reduced dry weights and enhanced oxidative burst. Although all the three PAs as well as AM inoculations upsurge plant growth by remarkably lowering Ni transport as well as the sequential oxidative burden, AM was most effective, followed by Put, Spd with least positive impact of Spm. The combined applications of AM and Put were able to strengthen antioxidant defense mechanisms, including those of ascorbate-glutathione cycle, most strongly when compared with + Spd + AM and + Spm + AM. Pusa 2001 was more responsive to PAs priming because of its proficiency to develop better effective mycorrhizal symbiosis with R. intraradices when compared with AL201. Hence, the results suggest use of combined applications of PAs (mainly Put) and R. intraradices as an effective strategy for mitigating Ni toxicity in pigeonpea genotypes. Keywords Antioxidants . Arbuscular mycorrhiza . Nickel . Pigeonpea . Polyamines . ROS Introduction Nickel (Ni) belongs to group VIII B of the transition series and ranks 28th in the periodic table. It is a vital micronutrient for plants growth and development because it is required in es- sential metabolic processes (Liu 2001; Sachan and Lal 2017; Patra et al. 2019). However, at raised concentrations in soil and water, it is considered as wide-scale pollutant (Sreekanth et al. 2013) and is discharged into the soil by numerous natural and human-induced sources (Bhalerao et al. 2015; Soares et al. 2016). High concentrations of Ni in the soil adversely affect plant growth by increasing membrane permeability which causes electrolyte leakage, decrease photosynthe- sis, N 2 -fixing efficiency, nutrient status, and yield of the plants (Saad et al. 2016; Garg and Saroy 2019). In addi- tion to this, high concentration of Ni also generates reac- tive oxygen species (ROS) as well as induce oxidative injury as reported in Solanum nigrum (Soares et al. 2016 ), Glycine max (Sirhindi et al. 2016 ), soybean (Barcelos et al. 2018; Mir et al. 2018), etc. In order to detoxify ROS, plant tissues upregulate the ac- tivities of enzymatic antioxidants like superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (GPOX) and en- zymes of ascorbate-glutathione (AsA-GSH) cycle—ascorbate Responsible Editor: Philipp Gariguess Highlights •Ni stress had negative correlation with growth, mycorrhizal colonization, and ROS. •Put seed priming was more effective in reducing oxidative stress than Spd and Spm. •AM was more effective than PAs in modulating ascorbate-glutathione (AsA-GSH) cycle. •Functional complementarity between AM and PAs in reducing Ni uptake was recorded. •+Put + AM was most promising in imparting Ni tolerance to pigeonpea genotypes * Neera Garg gargneera@gmail.com; garg_neera@yahoo.com 1 Department of Botany, Panjab University, Chandigarh 160014, India Environmental Science and Pollution Research https://doi.org/10.1007/s11356-021-13878-7