Mitigation of cadmium accumulation in rice by eggshell-derived carbon dots: Insights into iron plaque formation

Preventing chronic cadmium (Cd) exposure in humans necessitates limiting Cd transfer from soil to rice. Nano-materials have demonstrated potential in alleviating Cd stress in plants, yet the precise effects and mechanisms of biomass carbon dots on Cd resistance remain incompletely characterized. This investigation delved into physiological and molecular mechanisms underlying the ameliorative effects of eggshell-derived carbon dots (Ca-CDs) on Cd-stressed rice. Our findings indicated that Ca-CDs enhanced rice yield by 39.8 % and decreased Cd accumulation in grains by 17.8 %. Perl's blue staining of rice roots revealed that Ca-CDs augmented the iron plaque formation under Cd stress. Additionally, the Non-invasive Micro-test Technology (NMT) and qPCR analyses indicated that Ca-CDs induced Ca²⁺ influx, upregulated the expression of OsCDPK5 and OsRBOHA, thereby triggering programmed cell death (PCD) and promoting a well-structured aerenchyma formation. Concurrently, Ca-CDs elevated the net photosynthetic rate (Pn) and electron transfer rate (ETR) by 21.4 % and 14.6 %, respectively, enhancing radial oxygen loss (ROL). These results elucidated the mechanism by which Ca-CDs facilitated iron plaque formation, presenting a promising strategy for mitigating Cd contamination in paddy fields.