Effect of Grain Position in a Panicle and Varieties on As,Cd,Cr,Ni,Pb Contents in Grains of Late japonica Rice

Two japonica rice varieties, a compact panicle type variety (CP) Xiushui 63 and a loose panicle type variety (LP) Xiushui 11, were grown in a slightly contaminated paddy field to determine the effect of grain position within a panicle and varieties on toxic heavy metal content in rice grains. There was a significant variation in heavy metal content among grains within a panicle. Furthermore, this variation varied with variety and metal. Shch as, Xiushui 63 showed higher variation than Xiushui 11, and As, Cd, Cr and Pb had a significant variation, while no significant variation for Ni. The top grains (TG) in a panicle had higher As, Cd and Ni contents compared with the middle ones (MG), and the bottom grains (BG) had the lowest. With regard to Cr and Pb, the case was opposite. The significantly positive correlations were found between grain weight and As, Cd, Ni contents in grains, but negative for grain weight and Cr, and Pb content. There was a remarkable difference in grain filling pattern among grains within a panicle, and between Xiushui 63 and Xiushui 11. In comparison with middle grains and top grains in a panicle, the bottom ones had lower grain filling rate and grain weight, leading to obvious difference in grain weight among grains within a panicle, and Xiushui 63 had significantly larger difference than Xiushui 11. There were significant and positive correlations between As, Cd, Ni content in grains and the maximum grain filling rate, but negative between the contents of these elements in grains and the time reaching the maximum grain filling rate. Concerning Cr and Pb, the case was just opposite. It is suggested that the accumulation of As, Cd and Ni is accompanied by accumulation of carbohydrates in rice grains.