Radial oxygen loss and iron plaque function as an integrated system to mitigate the cadmium accumulation in water spinach

Background and aimsWater spinach readily uptakes cadmium (Cd), posing a risk to human health. Selecting low-Cd cultivars is a promising mitigation strategy, but its extensive utilization is limited without a clear understanding of the critical plant factors determining Cd accumulation. This study aimed to elucidate the effects and interactions of the radial oxygen loss (ROL) and iron (Fe) plaque on the Cd accumulation in different water spinach cultivars and the underlying mechanisms.MethodsA pot and four hydroponic experiments using ten water spinach cultivars were conducted with different aeration, Fe supply, and Cd stress treatments.ResultsThe Cd accumulation of different cultivars was determined by both root uptake and root-to-shoot transport. There were 4.0-, 3.8- and 6.3-fold differences among different cultivars in ROL, Fe plaque, and shoot Cd accumulation, respectively. Rhizosphere and root Fe plaque reduced root Cd uptake and were regulated by Fe supply and ROL. Increased ROL under stagnant conditions enhanced Fe plaque and induced its redistribution along root axes. Root Cd retention through compartmentalization and chelation inhibited root-to-shoot Cd translocation.ConclusionThe Fe plaque, ROL, and root Cd retention formed an interactive system to decrease the Cd uptake and accumulation in water spinach. Low-Cd cultivars exhibited higher ROL, greater Fe plaque and more effective root Cd retention, and responded to stagnant conditions with greater ROL increases and more enhanced Fe deposition on root surfaces. This study provides new insights into the Cd accumulation mechanisms in water spinach and a theoretical basis for selecting low-Cd cultivars.

Automated summary

This study investigated the effects and interactions of radial oxygen loss (ROL) and iron (Fe) plaque on Cd accumulation in different water spinach cultivars. The results showed that a system composed of Fe plaque, ROL, and root Cd retention decreased Cd uptake and accumulation in water spinach. Low-Cd cultivars exhibited higher ROL, greater Fe plaque, and more effective root Cd retention.