Cobalt oxide nanoparticles aggravate DNA damage and cell death in eggplant via mitochondrial swelling and NO signaling pathway

BACKGROUND: Despite manifold benefits of nanoparticles (NPs), less information on the risks of NPs to human health and environment has been studied. Cobalt oxide nanoparticles (Co(3)O(4)-NPs) have been reported to cause toxicity in several organisms. In this study, we have investigated the role of Co(3)O(4)-NPs in inducing phytotoxicity, cellular DNA damage and apoptosis in eggplant (Solanum melongena L. cv. Violetta lunga 2). To the best of our knowledge, this is the first report on Co(3)O(4)-NPs showing phytotoxicity in eggplant. RESULTS: The data revealed that eggplant seeds treated with Co(3)O(4)-NPs for 2 h at a concentration of 1.0 mg/ml retarded root length by 81.5 % upon 7 days incubation in a moist chamber. Ultrastructural analysis by transmission electron microscopy (TEM) demonstrated the uptake and translocation of Co(3)O(4)-NPs into the cytoplasm. Intracellular presence of Co(3)O(4)-NPs triggered subcellular changes such as degeneration of mitochondrial cristae, abundance of peroxisomes and excessive vacuolization. Flow cytometric analysis of Co(3)O(4)-NPs (1.0 mg/ml) treated root protoplasts revealed 157, 282 and 178 % increase in reactive oxygen species (ROS), membrane potential (ΔΨm) and nitric oxide (NO), respectively. Besides, the esterase activity in treated protoplasts was also found compromised. About 2.4-fold greater level of DNA damage, as compared to untreated control was observed in Comet assay, and 73.2 % of Co(3)O(4)-NPs treated cells appeared apoptotic in flow cytometry based cell cycle analysis. CONCLUSION: This study demonstrate the phytotoxic potential of Co(3)O(4)-NPs in terms of reduction in seed germination, root growth, greater level of DNA and mitochondrial damage, oxidative stress and cell death in eggplant. The data generated from this study will provide a strong background to draw attention on Co(3)O(4)-NPs environmental hazards to vegetable crops.