Browsing by Author "Hu, Ruifang"

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    How manganese affects rice cadmium uptake and translocation in vegetative and mature plants
    (Plant and Soil, 2024-04-19) Hu, Ruifang; Limmer, Matthew A.; Seyfferth, Angelia L.
    Background and aims Rice is prone to Cd uptake under aerobic soil conditions primarily due to the OsNramp5 Mn transport pathway. Unlike Cd, Mn availability in rice paddies decreases as redox potential increases. We tested whether increasing Mn concentrations in solution would decrease Cd accumulation in rice through competition between Mn and Cd for uptake and/or suppression of OsNramp5 expression. Methods Rice was grown to maturity under Mn concentrations that spanned three orders of magnitude (0.30 to 37 μM) that corresponded to free Mn2+ activities of 10–7.9 to 10–5.0 M while free Cd2+ activity was held as constant as achievable (10–10.2 to 10–10.4 M). Plant biomass and elemental concentrations were measured in roots and shoots at each stage. Fold changes in the expression of OsNramp5, OsCd1, OsHMA3, OsCCX2, and OsYSL6 genes in vegetative and grain-filling stages of rice plants were determined. Results Competition between Mn and Cd for root uptake and accumulation in shoots was observed at the highest concentration of Mn tested. OsNramp5 expression was significantly higher in rice plants at the vegetative stage compared to the grain-filling stage, while OsCd1 and OsHMA3 showed the opposite. Solution Mn concentrations previously thought to be tolerable by rice grown to the vegetative stage led to Mn toxicity as plants matured. Conclusions Mn competes with Cd during uptake into rice with OsNramp5 expression unaffected. Different translocation paths may occur for Mn and Cd within the rice plant and over the rice life cycle, with OsCCX2 correlated with shoot Cd concentration.
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    Rice uptake of cadmium and arsenic: evaluation, uptake mechanism and mitigation
    (University of Delaware, 2022) Hu, Ruifang
    Arsenic (As) and cadmium (Cd) are two trace elements that can be taken up and accumulated in rice (Oryza sativa L.). Rice is a globally important staple food, and As or Cd uptake could potentially pose health risks for rice consumers because both elements are categorized as a human carcinogen. In order to estimate and control the health risk posed by As and Cd in rice grain, it is important to evaluate rice grain As and Cd concentrations, understand how soil chemical parameters and water managements affect As and Cd uptake, and understand the uptake and translocation mechanism of Cd in rice. In this dissertation, rice As and/or Cd concentrations were evaluated from three rice production regions, where rice As and/or Cd levels were not previously reported. In addition, the impact of rice paddy soil chemical parameters and water managements on rice As and Cd uptake were investigated, and the impact of Mn availability on Cd uptake and translocation in rice were investigated at both chemical and the plant molecular level. Rice grain grown in smallscale rice farms in the northeastern United States and in Everglades Agricultural Area (EAA) in southern Florida were found to pose little As and Cd health risks for rice consumers. In contrast, rice grain produced in Cambodia may pose Cd health risks for rice consumers. Soil As or Cd concentrations, water management, and soil pH were found to be important factors influencing rice As and/or Cd uptake. Higher Mn activity in hydroponic rice study was found to compete with Cd for uptake transporter OsNramp5 into rice plant. However, the decreased Cd concentration or mass accumulation in rice grain was not as significant as in rice root under higher Mn activity. The data suggest that grain Cd accumulation was also complicated by Cd root to shoot and shoot to grain translocation, which likely differs from Mn translocation pathways within rice plant but involved with Cd transporter OsCCX2. These findings have implications for the role of Mn as a Cd mitigation strategy and should be further explored.