Calcium-Dependent Hydrogen Peroxide Mediates Hydrogen-Rich Water-Reduced Cadmium Uptake in Plant Roots

Hydrogen gas (H ) has a possible signaling role in many developmental and adaptive plant responses, including mitigating the harmful effects of cadmium (Cd) uptake from soil. We used electrophysiological and molecular approaches to understand how H ameliorates Cd toxicity in pak choi ( ssp. ). Exposure of pak choi roots to Cd resulted in a rapid increase in the intracellular H production. Exogenous application of hydrogen-rich water (HRW) resulted in a Cd-tolerant phenotype, with reduced net Cd uptake and accumulation. We showed that this is dependent upon the transport of calcium ions (Ca ) across the plasma membrane and apoplastic generation of hydrogen peroxide (H O ) by respiratory burst oxidase homolog (BcRbohD). The reduction in root Cd uptake was associated with the application of exogenous HRW or H O This reduction was abolished in the mutant of Arabidopsis ( ), and pak choi pretreated with HRW showed decreased transcript levels. Roots exposed to HRW had rapid Ca influx, and Cd-induced Ca leakage was alleviated. Two Ca channel blockers, gadolinium ion (Gd ) and lanthanum ion (La ), eliminated the HRW-induced increase in expression, H O production, and Cd influx inhibition. Collectively, our results suggest that the Cd-protective effect of H in plants may be explained by its control of the plasma membrane-based NADPH oxidase encoded by which operates upstream of IRT1 and regulates root Cd uptake at both the transcriptional and functional levels. These findings provide a mechanistic explanation for the alleviatory role of H in Cd accumulation and toxicity in plants.