Effects of Cr₂O₃ nanoparticles on the chlorophyll fluorescence and chloroplast ultrastructure of soybean (Glycine max)

Chromic oxide nanoparticles (Cr₂O₃ NPs) are widely used in commercial factories and can cause serious environmental problems. However, the mechanism behind Cr₂O₃ NP-induced phytotoxicity remains unknown. In this study, the effects of Cr₂O₃ NPs on the growth, chlorophyll fluorescence, SEM-EDS analysis, and chloroplast ultrastructure of soybean (Glycine max) were investigated to evaluate its phytotoxicity. The growth of soybean treated with various Cr₂O₃ NP suspensions (0.01, 0.05, 0.1, and 0.5 g L⁻¹) was significantly inhibited. Specially, shoot and root biomass decreased by 9.9 and 46.3%, respectively. Besides, the maximum quantum yield of PSII (Fv/Fm) as well as the photochemical quenching (qP) decreased by 8–22 and 30–37%, respectively, indicating that the photosynthetic system was damaged when treated with Cr₂O₃ NPs. Moreover, the inhibition was confirmed by the reduction of Rubisco and MDH enzyme activity (by 54.5–86.4 and 26.7–96.5%, respectively). Overall, results indicated that the damage was caused by the destruction of chloroplast thylakoid structure, which subsequently reduced the photosynthetic rate. Our research suggests that Cr₂O₃ NPs can be transported and cause irreversible damage to soybean plants by inhibiting the activity of electron acceptors (NADP+) and destroying ultrastructure of chloroplasts, providing insights into plant toxicity issues. .