Genotypic Difference Of Mercury Tolerance And Genetic Analysis Of Mercury-Tolerant Gene In Rice (Oryza Sativa L.)

Mercury (Hg) pollution has become a worldwide environmental problem. Hg is one of the most toxic heavy metals to living organisms and there is no known beneficial biological function. To investigate the mechanism of Hg tolerance and accumulation, eight rice genotypes were compared under Hg stress and genetic analysis of Hg-tolerant gene was studied. The results are summarized as follows:1. Hg²⁺-tolerance among eight rice genotypes at germination and seedling stage was compared using 0.08 mmol/L HgCl₂. The results showed that the germination rate decreased with the increasing of Hg²⁺ concentration. The germination rate of Kasalath has the largest decline, whereas that of 9311 was little affected by Hg²⁺ treatment. Root tolerance index and shoot relative biomass of 9311 were much higher than the other genotypes. Hg²⁺ content in roots and leaves were different among eight rice genotypes. IR1552 and IR64 accumulated more Hg²⁺ than Kasalath, Azucena and Nipponbare.2. A doubled haploid (DH) population of 96 lines derived from the cross between an Hg-sensitive and less-accumulative japonica variety Azucena and an Hg-tolerant and highly-accumulative indica variety IR64, was used to identify the QTLs. Relative shoot height (RSH), relative shoot dry weight (RSDW), and relative total dry weight (RTDW) were evaluated in nutrient solutions with or without 0.08 mmol/L HgCl₂. Four QTLs were detected for Hg tolerance with IR64 contributing favorable alleles. Three QTLs for Hg accumulation including two for Hg concentration in leaves (HgL) and one for Hg concentration in roots (HgR) were determined. The analysis revealed five pairs of epistatic loci for Hg tolerance and two pairs of epistatic loci for Hg accumulation in rice seedlings.3. A major QTL on chromosome 1 between markers R210 and AMY1B for RTDW could explain 36% of the phenotypic variation. Ten Hg-induced genes located in this interval were screened out by semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). The expression of ten genes in Azucena and IR64 was different under 0.08 mmol/L HgCl₂ stress.