Genetic Diversity Of Cadmium Accumulation Characteristics And Gene Expression Levels Among Rice Genotypes

The absorption and accumulation characteristics of cadmium have significant genetic differences among rice varieties.These differences are closely related to the transp ort efficiency of cadmium ions and other ions.Natural resistance-associated macrophage protein(NRAMP)genes in rice play an important regulatory role on the transport of divalent metal ions.In order to learn the relationship between gene expression level and cadmium accumulation,hydroponics and pot experiments with different rice genotypes were conducted.The expression of NRAMP genes in developing grains of rice was determined by real-time quantitative polymerase chain reaction(RTPCR).The main results are as follows:(1)Cadmium accumulation in roots and shoots are significant different among 12 genotypes.Xiangzaoxian 24 and Zhaoyang 1B belong to low cadmium accumulation genotype.Sanbaili,Nanjing 11,Jiayu 948,Fupin 36 and Xiangzaoxian 705 belong to high cadmium accumulation genotype.The roots of low cadmium accumulation genotypes displayed a weak ability to absorb cadmium and transport cadmium to shoots,while the roots of high cadmium accumulation genotypes displayed a strong ability to do that.Average content of cadmium in shoots and roots from the twelve genotypes was 29.96 mg·kg-1 and 872.06 mg·kg-1,respectively.Average transfer factor of cadmium from roots to shoots was 0.03.(2)Cadmium accumulation in grains and rachises of detached panicles are significant different among 10 genotypes.Cadmium accumulation in grains and rachises are in the range of 0.08~0.27 mg·kg-1 and 0.02~0.10 mg·kg-1,respectively.The transfer factor of cadmium from rachises to grains was in the range of 0.07~0.35 when Zhaoyang 1B,Fupin 36,Xiangzaoxian 705 and Xiangzaoxian 24 exposed to 0.9 ~5.4 μM cadmium solution.According to the changing trend of cadmium accumulation in rice under different cadmium stress,rice genotypes can be divided into 4 types based on cadmium accumulation: low and stable genotype,high and stable genotype,low and growth-oriented genotype,high and growth-oriented genotype.Zhuzhen B,Zhaoyang 1B,Liusha 1 and Erjiunan 1 belong to low and stable genotype.Fupin 36 belong s to high and stable genotype.Zhenxian 97 B and Xiangzaoxian 24 belong to low and growth-oriented genotype.Jiayu 948,Tanzao 215 and Xiangzaoxian 705 belong to high and growth-oriented genotype.(3)Cadmium accumulation in grains and the transfer factor of cadmium from rachises to grains are significantly different among genotypes when rice plants grew in cadmium contaminated soil in pots.Among 7 genotypes,Zhaoyang 1B displayed the lowest cadmium content of 0.01 mg·kg-1 in grains.Xiangzaoxian 705 had highest cadmium content of 0.06 mg·kg-1 in grains.Zhaoyang 1B had the lowest cadmium transfer factor of 0.0840 from rachises to grains.Xiangzaoxian 705 had the highest cadmium transfer factor of 0.3624 from rachises to grains.(4)Expression levels of Os Nramp1～3 and Os Nramp5 in rice developing grains are significantly different among 4 genotypes.Expression level of Os Nramp5 in rice developing grains is positively correlated with cadmium accumulation in grains aa well as with the cadmium transport capacity from rachises to grains.Zhaoyang 1B is a low cadmium accumulation genotype,and the ability of cadmium transport from rachises to grains is the weakest.At the fifth day after flowering,the amount of relative expression of Os Nramp5 in the developing grains of Zhaoyang 1B is the lowest.Xiangzaoxian 705 is a high cadmium accumulation genotype,and the ability of cadmium transport from rachises to grains is the strongest.At the fifth day after flowering,the amount of relative expression of Os Nramp5 in the developing grains of Xiangzaoxian 705 is the highest.