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 (HO) by respiratory burst oxidase homolog (BcRbohD). The reduction in root Cd uptake was associated with the application of exogenous HRW or HO 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, HO 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.