Calcium-Mobilizing Properties of <i>Salvia miltiorrhiza</i>-Derived Carbon Dots Confer Enhanced Environmental Adaptability in Plants

Biomass-derived carbon dots (CDs) are promising nanotools for agricultural applications and function as a reactive oxygen species (ROS) scavenger to alleviate plant oxidative stress under adverse environments. Nevertheless, plants need ROS burst to fully activate Ca²⁺-regulated defensive signaling pathway. The underlying mechanism of CDs to improve plant environmental adaptability without ROS is largely unknown. Here, <i>Salvia miltiorrhiza</i>-derived CDs triggered ROS-independent Ca²⁺ mobilization in plant roots. Mechanistic investigation attributed this function mainly to the hydroxyl and carboxyl groups on CDs. CDs-triggered Ca²⁺ mobilization was found to be dependent on the production of cyclic nucleotides and cyclic nucleotide-gated ion channels. Lectin receptor kinases were verified as essential for this Ca²⁺ mobilization. CDs hydroponic application promoted Ca²⁺ signaling and plant environmental adaptability under salinity and nutrient-deficient conditions. All these findings uncover that CDs have a Ca²⁺-mobilizing property and thus can be used as a simultaneous Ca²⁺ signaling amplifier and ROS scavenger for crop improvement.