Relationships Between Subcellular Distribution and Translocation and Grain Accumulation of Pb in Different Rice Cultivars

To test the hypothesis that lead (Pb) content of rice grain may be related to its transport and subcellular distribution in rice plant, the present study was conducted with six rice cultivars of different types under different soil Pb levels. The results showed that grain Pb concentrations were correlated positively and significantly ( P < 0.05 or 0.01) with distribution ratios (DRs) of Pb from shoots to ears/grains, but insignificantly ( P > 0.05) with the DR from roots to shoots. The DR from shoots to ears/grains was correlated positively and significantly ( P < 0.05 or 0.01) with subcellular distribution ratios (SDRs) of Pb in soluble fraction of shoots, but negatively and significantly ( P < 0.05 or 0.01) with the SDR in cell wall fraction of shoots. In conclusion, Pb transportation from the shoot to the grain is the key factor in determining Pb content of rice grain. The Pb distributed in soluble fraction of shoot tissue is the key source of Pb for transferring into the grain. The Pb precipitated in cell wall fraction is the key sink of Pb in shoot tissue that restricts the transport of Pb from the shoot to the grain.