Star Polymers with Designed Reactive Oxygen Species Scavenging and Agent Delivery Functionality Promote Plant Stress Tolerance.

Plant abiotic stress induces reactive oxygen species (ROS) accumulation in leaves that can decrease photosynthetic performance and crop yield. Materials that scavenge ROS and simultaneously provide nutrients in vivo are needed to manage this stress. Here, we incorporated both ROS scavenging and ROS triggered agent release functionality into an ∼20 nm ROS responsive star polymer (RSP) poly(acrylic acid)- block -poly((2-(methylsulfinyl)ethyl acrylate)- co -(2-(methylthio)ethyl acrylate)) (PAA- b -P(MSEA- co -MTEA)) that alleviated plant stress by simultaneous ROS scavenging and nutrient agent release. Hyperspectral imaging indicates that all of the RSP penetrates through the tomato leaf epidermis, and 32.7% of the applied RSP associates with chloroplasts in mesophyll. RSP scavenged up to 10 μmol mg -1 ROS in vitro and suppressed ROS in vivo in stressed tomato ( Solanum lycopersicum ) leaves. Reaction of the RSP with H 2 O 2 in vitro enhanced the release of nutrient agent (Mg 2+ ) from star polymers. Foliar applied RSP increased photosynthesis in plants under heat and light stress compared to untreated controls, enhancing the carbon assimilation, quantum yield of CO 2 assimilation, Rubisco carboxylation rate, and photosystem II quantum yield. Mg loaded RSP improved photosynthesis in Mg deficient plants, mainly by promoting Rubisco activity. These results indicate the potential of ROS scavenging nanocarriers like RSP to alleviate abiotic stress in crop plants, allowing crop plants to be more resilient to heat stress, and potentially other climate change induced abiotic stressors.