Accumulation and Effect of Manganese on Chloroplasts and Antioxidant Responses in Arabidopsis Thaliana

In this study, 5-day-old seedlings of Arabidopsis thaliana were exposed to 0, 0.5, and 1.0 mmol/L MnCl₂ for 6 days by using three independent biological replicates. The results indicated that Mn content in roots exhibited a dose-dependent increase with rising external Mn supply. The elevated Mn levels led to significant reductions in the nutrient content of K, Ca, Na, and Fe in roots. In addition, exposure to 0.5 and 1.0 mmol/L Mn decreased the content of chlorophyll. Both 0.5 and 1.0 mmol/L Mn decreased chlorophyll fluorescence intensity as observed by confocal microscopy. The activities of catalase, superoxide dismutase, and peroxidase were reduced by 0.5 and 1.0 mmol/L Mn in roots. The treatment with 0.5 and 1.0 mmol/L Mn led to a substantial accumulation of malondialdehyde (MDA) and H₂O₂. In contrast, the reduced glutathione (GSH) content exhibited an opposite trend. Moreover, Mn exposure decreased the mitochondrial membrane potential (ΔΨm) but increased the fluorescence of reactive oxygen species in root cells by laser scanning confocal microscopy. In summary, this study highlights that Mn toxicity impairs photosynthesis, disrupts antioxidant defenses, and induces oxidative damage in the seedlings of Arabidopsis thaliana.