Variations Among Rice Cultivars In The Uptake And Translocation Of Cadmium And Lead From Soil,and The Mechanisms

Cadmium (Cd) and lead (Pb) are important contaminants in agricultural soil, and put great threaten to agriculture and human health. Rice is one of the most important crops in the world and the first crop in Asia. So the purposes of this research are mean to investigate the differences among rice cultivars in the uptake, translocation and accumulation of Cd and Pb from soil, and the mechanisms. The results are useful in the breeding and selecting of rice cultivars, and in other methods for reducing rice Cd and Pb contamination. The main contents of this research are showed below: 1. Studying on the differences among rice cultivars in the uptake and accumulation of Cd and Pb from soil, with Cd or Pb concentrations in brown rice as main index, and with rice cultivars of various types from different origins as materials, and screening for typical rice cultivars with large variations among them in Cd uptake and translocation to grain. 2. The variations among the typical rice cultivars in Cd uptake, translocation and accumulation, and the order of nature. 3. The mechanisms for the differences among rice cultivars in Cd uptake and translocation. The major results were showed as follow:1. Variations among rice cultivars (types) in Cd uptake and translocationThere were wide variations (more than 10-fold) among rice cultivars in Cd concentrations of straw and brown rice. Indica, Hybrid Indica and New Plant Type were significantly higher than Japonica and Hybrid Japonica in terms of Cd concentration in brown rice, and the differences between origins were not significant.The differences among six typical rice cultivars in Cd concentrations, quantity accumulations and distributions in rice plant varied with plant organs, with greater differences in fruit organs (the panicle of heading stage and grain of maturity stage) and smaller differences in roots, stems and leaves. In the six typical rice cultivars, the cultivars with Indicaconsanguinity were higher than the cultivars with Japonica consanguinity with regard to Cd concentrations and quantity accumulations in all organs and the distribution ratios of Cd to fruit organs.Poor correlations existed between different organs of a same growth stage in Cd concentrations, but good correlations between different growth stages of a same organ. There were somewhat correlations between organs in Cd quantity accumulation, and good correlations between root, stem, leaf and fruit organs.Cd was not distributed uniformly in different parts of grain structure. Cd concentrations of cortex were much higher than that in chaff and polished rice. Cd accumulated in polished rice was 45.4% of that in grain, smaller portion in cortex, and smallest portion in chaff. So 54.6% of the Cd in grain was take away after grain processing.Grain Cd concentration correlated significantly and positively with total Cd accumulated in rice plant, distribution ratio of Cd to aboveground part, and distribution ratio of Cd from straw to grain. There were significant correlations between Cd concentrations in brown rice and some agronomic characteristics.Cd concentrations in brown rice and straw were related to Cd accumulation speeds in them, but not to the days of Cd accumulation.2. Differences among rice cultivars in tolerance to Cd and the evaluationindicesGreat differences existed between rice cultivars in their tolerance to Cd, respecting growth and development of rice plant. The tiller number, plant height, area of green leaf, plant dry weight and grain yield were affected by Cd. The degrees of Cd damage on them varied largely with rice cultivars, such as the reduction of grain yield varied from 2.90% to 20.08% among the six typical rice cultivars under soil Cd treatment. According to dry matter accumulation, the tolerance of rice to Cd went stronger with the advance of growing stages. The decreases of spikelet number in panicle were the main cause for grain yield reduction under soil Cd treatment.Under soil Cd treatment, some physiological indices of leaf were changed, such as leaf conduct...