Studies On Screening For Genotypes With Low Concentration Of As, Cd, Pb And Its Transportation In Rice (Oryza Sativa L.)

Selection and breeding low heavy metal accumulation varieties or decreasing their absorption from growth soil were the most immediate and effective ways to control heavy metal concentration in rice(Oryza sativa L.). As the concentration of heavy metal in the kernels were related to their absorption, transportation and accumulation in rice plant, it was important to research the characteristics of absorption and transportation in rice, especially the migrating regularity of heavy metal to economy organ. In present paper, inductively coupled plasma-mass spectrometry(ICP-MS) was used to detect arsenic(As), cadmium(Cd) and lead(Pb) concentration of brown rice in 78 varieties, and of aboveground organs in different growth stages of variety Zheyou 12. The major amid was to screening rice genotypes with low As, Cd, Pb concentration and to explore regularity of their transportation in rice. Results are as follows:1. The As, Cd, Pb concentration of brown rice of 78 varieties was determined. Simultaneously, As, Cd, Pb concentration of brown rice of 20 varieties, wich were grown in three field trials with different As, Cd, Pb concentration was compared. The results were showed that there is remarkable difference in accumulation of As, Cd, Pb in brown rice among varieties, and there are more polymorphisms in genotypes of Cd and Pb concentration than that of As. Correlation analyses showed that Cd concentration in brown rice have most positively correlation with Pb concentration(P<0.01). Out of 78 varieties, we obtained five genotypes of low Cd concentration and low Pb concentration in brown rice, one genotype of low Cd+As, two genotypes of low As+Pb, only one genotype of low As+Cd+Pb. t Test showed that environments have significant influence on As, Cd, Pb concentration in brown rice, and certain were at significant level. As,Cd and Pb expressed different responses to growth environments.2. The concentrations of As, Cd, Pb in aboveground organs at different growth stages, including seedling stage, tillering stage, heading stage, milk stage, dough stage and full ripe stage, were investigated using variety Zheyou 12 by experiments of water culture and field. Results showed that changes of As, Cd, Pb concentration in leaf and leaf sheath from seedling stage to full ripe stage present a U-shaped curve, the highest point at seedling stage and the lowest at heading stage. At the reproductive growth stage, the three elements showed different characteristics of transportation in different reproductive organs, but showed similar trend in kernels. Ultimately, the rank from high to low As concentration in aboveground organs was stalk>leaf>leaf sheath>spike stalk> glume>brown rice, and rank of Cd concentrations was stalk>leaf>leaf sheath>brown rice >spike stalk>glume, rank of Pb concentrations was leaf>leaf sheath>stalk>spike stalk> glume>brown rice, these results supported the regularity of decrease successively from root to top for heavy metal distribution in plant. Comparison with culture of water and field, the rank of Pb concentrations in different organs was the same as two experiments. Pb was higher concentration in leaf, and the lowest in brown rice, suggested that stalk and leaf of aboveground organs were the major parts for Pb accumulation in rice, and less transfered into the grain. Concentrations of As, Cd, Pb in the same aboveground organs in different growth stages in rice plants was As>Pb>Cd.3. Total As concentration of brown rice was investigated for 21 varieties grown in three field trials. Results showed that averages of total As concentration of brown rice express from high to low according to the total As concentration of growth soil. Analyzing the reaction of varieties to growth environments, it showed that most varieties exhibited different reaction to growth environment, but there were four stable varieties, for example, Minghui 70 consistently exhibited insensitive reaction, Minghui 86 exhibited sensitive reaction, Minghui 72 and Minghui 81 fell into intermediate category. Total brown rice, culm and growth soil environment of variety Zheyou 12 grown from fifteen tested field trials were measured, the average As concentration were soil> brown rice> culm in turn. Correlation analyses showed that As concentration of growth soil is no significant correlation to that of brown rice, and no negatively correlation to culm As concentration, but As concentration of brown rice has most positively correlation to that of culm.