Regulation of aluminum induced oxidative stress in Brassica via roles of sulfur metabolites and antioxidant responses mediated by a melatonin selenium nanocomposite

Melatonin (MT) and selenium (Se) are quite known in application in regulation of abiotic stress tolerance where metals remain important. Undoubtedly, MT being a signalling molecule and Se, a multivalent metalloid have been effective in metal stress alleviation individually, however, a limitation exists for insights in synergistic application. Thus, we formulated a special MT-dopped nano-selenium (SeNP-MT) against aluminum (Al) toxicity through oxidative stress is Brassica. This is more specified with illustration of Brassica seedlings where molecular and physiological regulation against Al stress remain less explored with exogenous application of SeNP-MT. Therefore, this study addresses the knowledge gap over the existing insights of nano-composites with special reference to integrated approaches of SeNP-MT that may modulate the regulatory pathways of Al tolerance. The synthesis of SeNP-MT was verified through opto-physical characteristics covering sizes, crystallinity, amorphous and repulsive nature, variations in functional bonds on surface. The investigation revealed that under 500 µM aluminum chloride (AlCl3) stress caused significant cellular lysis of root tissues. This was accompanied by the reduction of plant growth when plants were treated with varying doses of SeNP-MT1-3 (0.02—0.1 gL−1). The application of SeNP-MT2 showed an improvement in relative growth rate (RGR) (172.72%) along with minimization of Al uptake (21.87%). Similarly, tissue specific distribution of reactive oxygen species (ROS), chlorophyll fluorescence, photosystem II photochemical activities and malate decarboxylation reactions were regulated by SeNP-MT. Maximum accumulation of total sulfur (165.17%), cysteine (104.54%), non-protein thiol (22.50%), and phytochelatin (5.13%) content was maximum under SeNP-MT2 under Al stress. Additionally, SeNP-MT1-3 induced antioxidation pathways as recoded with increased glutathione peroxidase (GPX) and catalase (CAT) activities whereas maximum ratio (20.40%) of ascorbate to dehydro-ascorbate under SeNP-MT2 was observed. The genotoxicity tolerance was improved by modulating the loss of DNA studied through comet assay and related parameters. This study is scientific document which critically bridges the knowledge gap between individual effects of Se and MT and their synergistic impacts in a nanocomposite. The key regulatory pathways were found more effective under SeNP-MT application to mitigate the phytotoxicity of Al with Brassica and thereby establishes an emerging and bio-compatible nano-assisted tool for stress tolerance. The key findings in the present experiment emphasised that genomic stability, improved organic acid turnover are two essential pathways to regulate Al detoxification and bio-exclusion respectively. Thereby, the multifaceted activities underscore the efficiency of SeNP-MT might intervein Al tolerance in species that develops a biocompatible strategy for crop cultivation in acid rich Al polluted soil. Overall, the key findings emphasised the potential of nano augmented MT-Se formulation may open the unexplored pathways of Al tolerance at molecular level imparting resilience to other stresses also.