Spd-CDs-driven respiratory burst oxidase homolog/polyamine oxidase-dependent H2O2 signaling molecule engineering for salt tolerance in tomato

Carbon dots, are now considered safe, environment-friendly materials. Spermidine carbon dots (Spd-CDs) have been used as new agrochemicals for abiotic stress, but in-depth studies of salt stress remain scarce. Here, foliar application of Spd-CDs improved salt stress tolerance in tomatoes, and the beneficial effects were concentration-dependent. Tomato seedlings supplied with Spd-CDs (3.0 mg/L) had a greater height, a higher maximum quantum yield of PSII, and a higher net photosynthetic rate than controls after being exposed to 120 mM NaCl for 7 d. Molecular evidence showed that Spd-CDs promoted H₂O₂ molecule production by inducing the expression of respiratory burst oxidase homolog 1 (rboh1) and polyamine oxidase 5 (pao5), thus causing H₂O₂ molecule production and conferring resistance to salt stress. The role of RBOH1- and PAO5-dependent H₂O₂ molecule generation was evaluated by manipulating endogenous H₂O₂ levels and in rboh1 and pao5 mutants. Spd-CDs-meditated H₂O₂ regulation of salt tolerance could be articulated by reducing iron deficiency, maintaining ion homeostasis, and reducing root-to-shoot Na⁺ loading. Overall, the ROS signal molecule produced by RBOH1 and PAO5 protein was involved in the control of salt tolerance by Spd-CDs. These findings demonstrate that Spd-CDs are an effective and durable strategy to improve plant performance under salt stress, and to increase food security and quality.