Genotypic differences among rice cultivars in lead accumulation and translocation and the relation with grain Pb levels.

In order to understand the differences among rice cultivars and genotypes in lead (Pb) uptake and translocation, and their relationship with Pb accumulation in rice grains, pot soil experiments were carried out with six rice cultivars of diverse types under different soil Pb levels. The results showed that the differences among rice cultivars in Pb concentrations varied largely with plant organs, and the magnitudes of the differences were larger in ears and grains than in shoots and roots. Pb concentrations in ears and grains differed significantly (p<0.05) between rice types, and were in the order: Hybrid Indica>Indica>Japonica. Grain Pb concentrations were correlated significantly (p<0.05) with shoot Pb concentrations, and highly significantly (p<0.01) with ear Pb concentrations, but generally not with root Pb concentrations. The differences among rice cultivars in translocation factors (TF) of Pb from shoots to ears/grains were generally larger than the TF of Pb from roots to shoots. The differences among rice types in TF of Pb from shoots to ears/grains were generally significant (p<0.01 or 0.05), and the TF were in the order Hybrid Indica>Indica>Japonica. But the differences between rice types in the TF of Pb from roots to shoots were mostly insignificant (p>0.05). In general, grain Pb concentrations were correlated significantly (p<0.01 or 0.05) with the TF of Pb from shoots to ears/grains, but insignificantly (p>0.05) with the TF of Pb from roots to shoots. So the Pb in shoots, but not in roots, may be the main sources of Pb transferred to the grains. Pb concentrations in rice grains are likely to be determined mainly by the translocations of Pb from shoots to the grains, and little by the transport from roots to shoots. Pb concentration in ears of heading can be used as an index of Pb level in the grains.