The Difference in Growth and Four Microelement Concentrations Between Two Rice Genotypes Differing in Grain Cadmium-Accumulating Capacity

A pot experiment was conducted with two rice genotypes having different Cd concentrationsin their grains to study the effect of soil Cd level on biomass, Cd and Fe, Zn, Cr andPb accumulation in different plant parts. Cd was added into soil to form 4 levels, i.e.,0, 0.5, 2.5 and 12.5mgkg-1, respectively. The results showed that the Cd-induced reductionin biomass accumulation varied in both genotypes and growth stages. The Cd-inducedreduction in biomass became less with the progress of growth, and Xiushui63, a genotypewith relatively higher grain Cd concentration, was more severely inhibited than Xiushui217,a relatively lower Cd concentration. Both Cd concentration and accumulation in thevarious plant parts increased substantially with the increase of Cd levels. The differencebetween two genotypes in Cd concentration and accumulation became more pronounced withincreased Cd level as well as prolonged duration of exposure. Xuishui63 had much greaterCd accumulation than Xiushui217, in particular at late growth stage. Xuishui63 had aremarkably higher Cd translocation of roots to shoots than Xiushui217 in all Cd levels.The effect of Cd addition on four microelement concentrations in straw and milled ricealso varied in genotypes and Cd levels. Without Cd addition, Xiushui63 was significantlylower than Xiushui217 in the concentrations of all four elements in straw, while the casewas just opposite in milled rice. Zn, Fe and Pb concentrations decreased in milled ricewith the increase of Cd level, although the reduction extent differed in two genotypes.The results indicated that Cd concentration in rice grain is primarily dependent on theshoot Cd concentration, which is in turn mainly determined by Cd translocation from rootsto shoots.

Effect of Grain Position within a Panicle and Variety on As,Cd,Cr,Ni,Pb Concentrations in japonica Rice

Two japonica rice varieties, a compact panicle (CP) Xiushui 63 and a loose panicle (LP) Xiushui 11 were grown in a slightly contaminated paddy field, to determine the effect of grain positions within a panicle and variety on grain As, Cd, Cr, Ni and Pb concentrations. There was a significant difference in grain As, Cd, Cr, Ni and Pb concentrations among grain positions, and the extent of the difference was variety- and metal-specific; Xiushui 63 showed greater difference than Xiushui 11, and As, Cd, Cr and Pb being greater than Ni. The top grains (TG) of a panicle had higher As, Cd and Ni concentrations than the middle ones (MG), and the bottom ones (BG) contained the lowest. With regard to Cr and Pb, the case was opposite. Significantly positive correlations were found between grain weight and As, Cd, Ni concentrations, but there was a negative correlation between grain weight and Cr, and Pb concentrations. There was a remarkable variation in grain filling pattern among grains within a panicle, and between Xiushui 63 and Xiushui 11. In comparison with MG and TG, BG had the lowest grain filling rate and grain weight, leading to obvious difference in grain weight among grains within a panicle, and a greater difference for Xiushui 63 than for Xiushui 11. The regression analysis showed that grain As and Cd concentrations were positively correlated with the maximum grain filling rate (GRm),while negatively correlated with the required time for reaching the maximum grain filling rate (Tpol). Concerning Cr and Pb, the case was just reverse. It is suggested that As and Cd accumulation in grains might be accompanied by the carbohydrate accumulations, while Cr and Pb accumulation displayed a different pattern.