Mitigation of aluminum toxicity in rice seedlings using biofabricated selenium nanoparticles and nitric oxide: Synergistic effects on oxidative stress tolerance and sulfur metabolism

Biofabricated selenium nanoparticles (Se-NPs) and sodium nitroprusside-derived nitric oxide (NO) singly or in combination was evaluated to improve tolerance to aluminum (Al) stress in rice (Oryza sativa L. cv. Swarna Sub1). The major objective was to elucidate contribution of sulfur reduction processes in oxidative stress tolerance along with cellular responses. Rice seedlings were primed against Al stress (550 μM) by the exogenous application of 100 μM NO and 20 ppm Se-NPs synthesized from a Salvinia molesta D. Mitch. extract. Green-synthesized Se-NPs (∼67 nm) had a crystalline, amorphous structure, high stability with functional groups in capping agents. The seedlings reduced bioaccumulation of Al in root tissues under SNP, Se-NPs, and in combination. Bioexclusion of Al was done in endodermal tissues by callose formation and binding in a fluorescent complex in the root tips. An upregulation of sulfur metabolism, including total sulfur, cysteine, cysteine synthase, and ATP sulfurylase activity was modulated by SNP + Se-NPs combination. Oxidative stress inducing metal stress for membrane oxidation into malondialdehyde, superoxide radical, and hydrogen peroxide, were also moderated by the SNP + Se-NPs combination. The Al-induced oxidative stress was relieved by a proportionate increase in superoxide dismutase and peroxidase activity. A higher ratio of ascorbate to dehydroascorbate and reduced to oxidized glutathione induced by the SNP + Se-NPs combination was supported antioxidation. These findings may substantiate the efficiency of green-synthesized Se-NPs together with SNP (as an NO donor) for amelioration of Al hazardous in crops like rice.