10.1021/acsnano.7b05723.s001 Honghong Wu Honghong Wu Nicholas Tito Nicholas Tito Juan P. Giraldo Juan P. Giraldo Anionic Cerium Oxide Nanoparticles Protect Plant Photosynthesis from Abiotic Stress by Scavenging Reactive Oxygen Species American Chemical Society 2017 ratio leaf mesophyll cells Scavenging Reactive Oxygen Species Plant abiotic stress chloroplast vivo augments ROS abiotic stress exhibit plant nanobionics approach nanoceria ANC cerium oxide nanoparticles plant enzyme scavenger leaf ROS levels Arabidopsis thaliana plants photosynthesis reactive oxygen species Rubisco carboxylation rates sub -11 nm PNC Anionic Cerium Oxide Nanoparticles Protect Plant Photosynthesis abiotic stress carbon assimilation rates sub -11 nm II 2017-11-03 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Anionic_Cerium_Oxide_Nanoparticles_Protect_Plant_Photosynthesis_from_Abiotic_Stress_by_Scavenging_Reactive_Oxygen_Species/5588761 Plant abiotic stress leads to accumulation of reactive oxygen species (ROS) and a consequent decrease in photosynthetic performance. We demonstrate that a plant nanobionics approach of localizing negatively charged, sub-11 nm, spherical cerium oxide nanoparticles (nanoceria) inside chloroplasts <i>in vivo</i> augments ROS scavenging and photosynthesis of Arabidopsis thaliana plants under excess light (2000 μmol m<sup>–2</sup> s<sup>–1</sup>, 1.5 h), heat (35 °C, 2.5 h), and dark chilling (4 °C, 5 days). Poly­(acrylic acid) nanoceria (PNC) with a hydrodynamic diameter (10.3 nm)lower than the maximum plant cell wall porosityand negative ζ-potential (−16.9 mV) exhibit significantly higher colocalization (46%) with chloroplasts in leaf mesophyll cells than aminated nanoceria (ANC) (27%) of similar size (12.6 nm) but positive charge (9.7 mV). Nanoceria are transported into chloroplasts <i>via</i> nonendocytic pathways, influenced by the electrochemical gradient of the plasma membrane potential. PNC with a low Ce<sup>3+</sup>/Ce<sup>4+</sup> ratio (35.0%) reduce leaf ROS levels by 52%, including hydrogen peroxide, superoxide anion, and hydroxyl radicals. For the latter ROS, there is no known plant enzyme scavenger. Plants embedded with these PNC that were exposed to abiotic stress exhibit an increase up to 19% in quantum yield of photosystem II, 67% in carbon assimilation rates, and 61% in Rubisco carboxylation rates relative to plants without nanoparticles. In contrast, PNC with high Ce<sup>3+</sup>/Ce<sup>4+</sup> ratio (60.8%) increase overall leaf ROS levels and do not protect photosynthesis from oxidative damage during abiotic stress. This study demonstrates that anionic, spherical, sub-11 nm PNC with low Ce<sup>3+</sup>/Ce<sup>4+</sup> ratio can act as a tool to study the impact of oxidative stress on plant photosynthesis and to protect plants from abiotic stress.