Leaf photosynthesis and antioxidant capacity are rapidly restored by Mn3O4 nanoparticles in rice plants under Cd stress without affecting plant Cd concentration.

Nanomaterials have been increasingly applied to mitigate cadmium (Cd) stress in rice plants. However, whether foliar-applied nanomaterials can rapidly alleviate Cd toxicity within a shorter timeframe (e.g., <1 week) remains unclear. In this research, a hydroponic experiment involving rice plants was carried out, which consisted of control (CK), Cd stress, and Cd stress together with leaf application of polyacrylic acid coated Mn3O4 nanoparticles (Cd + PMO) treatments. Cd stress increased plant Cd concentration, reduced leaf photosynthesis and increased membrane lipid peroxidation, while Cd + PMO treatment (after application of PMO for 3 days) had no significant impact on plant Cd concentration but enhanced leaf photosynthetic rate by 71.1 % and reduced membrane lipid peroxidation by 32.3 % versus Cd treatment, respectively. Enhancement in leaf photosynthesis under Cd + PMO treatment relative to Cd stress was resulted from the improved mesophyll conductance and leaf biochemical capacity. Furthermore, the alleviated oxidative stress triggered by PMO under Cd stress resulted from the improvements in both enzymatic and non-enzymatic antioxidant systems. Importantly, our findings further indicate that glucosyltransferase and glutathione S-transferase have crucial roles in the rice tolerance to Cd stress, which is worthy of further study. Our present results should deepen our understandings of PMO effects on Cd tolerance of rice plants, and also providing a possible approach to rapidly reconstruct the crop performance in Cd-contaminated soils through leaf application of Mn3O4 nanoparticles, which is independent of plant Cd concentration.