Salvia Miltiorrhiza-Derived Carbon Dots as Scavengers of Reactive Oxygen Species for Reducing Oxidative Damage of Plants

Effective removal of excess reactive oxygen species (ROS) from plants is important to minimize biotic and abiotic stress and increase crop yield. Efficient natural ROS scavenging enzymes already exist; however, these enzymes are sensitive to environmental conditions, and it is challenging to produce them on a large scale. In this study, using biomass Salvia miltiorrhiza as the precursor, fluorescence carbon dots (CDs) were synthesized on a large scale using a one-step hydrothermal method. After a series of structural changes, the surface of CDs contains a S. miltiorrhiza-like polymer, which endows the CDs with high antioxidant capacity. These CDs have multiple enzyme activities with stronger antioxidant activity than that of the pure S. miltiorrhiza extract. CDs can scavenge DPPH•, O2•–, and •OH with excellent scavenging efficiencies of 88.9, 95.6, and 71.4%, respectively. Additionally, the corresponding enzyme activities are superior to those of the natural antioxidant Vc. The synthesized CDs not only have a good scavenging effect on intracellular ROS in plants but can also effectively alleviate the oxidative damage of Italian lettuce under salt stress. Compared with the control group, the root and leaf biomass of Italian lettuce significantly increased by 52.2 and 58.1%, respectively, the water content increased by 48.2%, and malondialdehyde (MDA) content decreased by 92.2%. This study provides a promising strategy for engineering biological antioxidant systems with multiple enzyme activities to attenuate plant biotic stress and abiotic stress.