Regulation of ascorbate-glutathione cycle by exogenous nitric oxide and hydrogen peroxide in soybean roots under arsenate stress

Highlights: • As^V alters root phenotype, length and fresh biomass • NO and H₂O₂ mitigate As^V stress in soybean root • NO and H₂O₂ trigger vacuolar sequestration of As • NO and H₂O₂ induce components of the ascorbate-glutathione cycle • H₂O₂ acts downstream of NO in responses of soybean roots under As stress The role of nitric oxide (NO) and hydrogen peroxide (H₂O₂) is well known for regulating plant abiotic stress responses. However, underlying mechanisms are still poorly understood. Therefore, the present study investigated the involvement of NO and H₂O₂ signalling in the regulation of arsenate toxicity (As^V) in soybean roots employing a pharmacological approach. Results show that As^V toxicity declined root length and biomass due to greater As accumulation in the cell wall and cellular organelles. Arsenate induced cell death due to enhanced levels of reactive oxygen species, lipid and protein oxidation and down-regulation in ascorbate-glutathione cycle and redox states of ascorbate and glutathione. These results correlate with lower endogenous level of NO. Interestingly, addition of L-NAME increased As^V toxicity. However, addition of SNP reverses effect of L-NAME, suggesting that endogenous NO has a role in mitigating As^V toxicity. Exogenous H₂O₂ also demonstrated capability of alleviating As^V stress, while NAC reversed the protective effect of H₂O₂. Furthermore, DPI application further increased As^V toxicity, suggesting that endogenous H₂O₂ is also implicated in mitigating As^V stress. SNP was not able to mitigate As^V toxicity in the presence of DPI, suggesting that H₂O₂ might have acted downstream of NO in accomplishing amelioration of As^V toxicity.