Characteristic Of Cadmium Uptake, Translocation And Accumulation In Cadmium-safe Rice Line

Rice （Oryza sativa L.） is one of the most important food cereal in China, therefore Cd translocation into the grains not only reduce their quality and safety, but also directly affect human health.The absorption and distribution of Cd in rice due to the different genotypes and species in interspecific differences in memory significantly.Thence, promoting the use of green, environmentally cadmium-safe ricecultivarhas become the key to solving Cd slightly polluted farmland in production safety.In this research, we have selected 5 potential cadmium-safe rice lines and 51 general rice lines according to the method of water culture and soil culture experiment. Then field experiment was conducted to investigate the differences of 56 rice lines on Cd uptake and distribution under pollution paddy field to selected cadmium-safe rice line again. Finally, we have analyzed the characteristics of the uptake, distribution and the subcellular distribution of Cd and the variation of non-protein thiols in the rice plants, to elucidate the possible differently existing mechanisms of Cd uptake transporters in the cadmium-safe rice line.（1） There were significant differences in the Cd concentrations and Cd accumulations among the 56 rice lines when the field soil Cd concentration was 13.89 mg·kg-1. Meanwhile, the Cd concentrations in brown rice ranged from 0.15 to 1.77 mg·kg-1 among the rice lines, the ratio of maximum and minimum value reached to 11.80 times, and the minimum value of Cd concentration was lower than the National Food Safety Standard （0.20 mg·kg-1）.The 56 rice lines were divided in to low accumulation lines, general lines and high accumulation lines depending on the Cd concentration of brown rice.The Cd concentration of brown rice of low accumulation lines was 0.20 mg kg-1 which was significantly lower than that of the general lines （0.65 mg·kg-1） and the high accumulation lines （1.57 mg·kg-1）. Moreover, due to the lower metastatic ability of Cd to grain, the low accumulation lines have lower Cd concentration in grain.Meanwhile, the distribution ratio of Cd accumulations in grain was 8.11 percent of the total Cd accumulations in aboveground of low accumulation lines, which was lower than that of the general lines （11.60%） and high accumulation lines （17.59%）.Among the low accumulation lines, the Cd concentrations in the brown rice of D62B, IRBN95-90 and GRlu 17/ai TTP//lu 172 were lower than the National Food Safety Standard. Thus, D62B, IRBN95-90 and GRlu 17/ai TTP//lu 17₂ can be considered as Cd safety rice germplasm resources for Cd-polluted farmlands.（2） The biomass and brown rice yield of three kinds of rice lines were inhibited significantly under different Cd stress in the late growth period. The brown rice yield of Luhuil7 declined by 62.62% at 16 mg Cd kg-1 and was more greatly affected than that of GRlu 17/ai TTP//lu 172 and D62B which declined by 43.60% and 48.42% compared with the plants in control.The Cd concentrations in different organs of the cadmium-safe rice lines, the general line and the high accumulation line increased significantly with the increasing Cd contents of soils （0-16mg-kg-1）. In addition, the Cd concentrations in different organs of the cadmium-safe rice line were significantly lower than those of the general line and the high accumulation line at all Cd levels. The distribution of root in the cadmium-safe rice line was significantly higher than those of the general line and the high accumulation line.Morever, the concentration of brown rice in the cadmium-safe rice lines was lower than the National Food Safety Standard（0.20 mg·kg-1） at 1 and 4 mg Cd kg-1, but the concentration of brown rice in the general lines and the high accumulation lines was exceeded 0.20 mg·kg-1 at all Cd levels.（3） The increase in Cd supply from 1 to 16 mg Cd kg-1 soil markedly increased Cd concentrations in xylem of different rice line. Meanwhile, the Cd concentrations in xylem of the cadmium-safe rice line were significantly lower than those of the general line and the high accumulation line at all Cd levels.The maximum difference among the three kinds of rice lines were also observed at 16 mg kg-1 Cd treatment. The Cd concentrations in xylem of the high accumulation line （R18） were 1.88,1.79 and 1.76 times higher than those of the cadmium-safe rice （D62B） at booting stage, heading stage and filling stage when the content of Cd in soil reached 16 mg kg-1. Morever, The Cd concentrations in xylem and in ear were in a positive and significant relationship, which suggested that reduced Cd transport to the grain in the late growth period is due to the higher Cd concentrations in root and the lower Cd concentrations in xylem.（4） The majority of Cd in shoot of D62B was associated with the cell walls at all Cd levels, while that of Luhuil7 was found occurring in the soluble fraction at 4 and 16 mg Cd kg-1. However, subcellular distribution of Cd in the root of D62B and Luhui17 showed that most of Cd was stored in the soluble fraction, followed by the cell walls and organelle fractions. It was suggested that the more Cd store in cell walls the lower Cd effectiveness in plants. Compared with the control groups, the increase in Cd supply from 1 to 16 mg Cd kg-1 significantly increased NPT of both rice lines. The NPT contents in D62B were significantly higher than those of Luhui17 at different Cd levels. Meanwhile, the NPT contents in roots of D62B were 1.40,1.28 and 1.38 times higher than those of Luhuil7 at 1,4 and 16 mg Cd kg-1. Cd accumulation in roots could be considered as the first barrier to defend against Cd toxicity. This could be attributed to the facts that higher contents of NPT to chelating Cd2+ by vacuolar compartmentalization and more Cd bound to cell walls in the roots was found in D62B.