Cerium chloride

Arabidopsis thaliana wild-type plants (Col-0) were grown on soil in the greenhouse or sown on 1/2x Murashige Skoog (MS) medium supplemented with the indicated chemicals under 16 h light /8 h dark, as described previously [29 (link)]. Rice plants (Oryza sativa ssp. japonica c.v. Nipponbare) were grown in water or indicated chemicals and incubated at room temperature. Benzothiadiazole S-methyl ester (BTH) and 5-(cyclopropylmethyl)-6-methyl-2-(2-pyridyl) pyrimidin-4-ol (PPA) were purchased from WAKO (Japan) and Maybridge (United Kingdom), respectively. Trypan blue, diaminobenzidine tetrahydrochloride (DAB) and cerium chloride were purchased from Sigma. Pseudomonas syringae pv. maculicola strain DG3 (virulent) was kindly obtained from Dr. Jean Greenberg and inoculated as described previously [30 (link)].

The cerium oxide nanoparticles synthesis was performed using a chemical precipitation technique for simplicity [12 (link)]. For each sample, cerium chloride (Sigma Aldrich, St. Louis, MO, USA, 0.5 g) has been added to distilled water (40 mL) with ammonium hydroxide (1.6 mL) added as a catalyst. Then, the solution is stirred at temperature of 50 °C for two hours at a stirring speed of 500 rpm, then the stirring is continued for 24 h at room temperature. The first heating step is important to avoid the formation of cerium hydroxide. After the full period of stirring, the sample is centrifuged and washed with ethanol to remove any reacted cerium chloride. Gold nanoparticles (Sigma Aldrich) of 20 nm diameter have been selected so that optical plasmonic resonance is in the same range of fluorescence emission of ceria nanoparticles, as will be shown later in the Results section. Gold nanoparticles are added in two ways: firstly added with the initial precursors before the stirring which we call it in-situ, and the second way is to add Gold nanoparticles as a post-synthesis step after the full synthesis of ceria nanoparticles. In both modes of gold addition, a 1 mL solution of Gold nanoparticles has been added to the ceria solution. Thus, the technique which leads to the highest intensity of fluorescence emission could be checked.