Hydroxyapatite nanoparticles in root cells: reducing the mobility and toxicity of Pb in rice

Nano-hydroxyapatite (nHAP) has high immobilization efficiency for reducing the lead (Pb) absorption of crops in Pb-contaminated soils. However, little information is available on the special and possible processes where nHAP in plant roots acts as a barrier, capturing Pb ions and decreasing Pb mobility in root cells. The internalization of nHAP in root cells with special attention given to the potential for reducing the toxicity and mobility of Pb in rice was investigated in hydroponic experiments using ICP, SEM-EDS and TEM-EDS techniques after exposure to Pb for 14 d. The results showed that nHAP existing in root cells was beneficial for alleviating Pb stress and restraining the translocation of Pb from roots to shoots. The primary mechanisms identified were: (a) the binding of Pb to the nHAP existing in root cells, reducing the interference of Pb ions with critical cell functions, and (b) the transformation of Pb ions into Pb-deposits in root cells, reducing the movement of Pb to the aerial parts. The result is useful for understanding the immobilization mechanisms of Pb in plant root cells by the application of environmental nanomaterials.