Genotypic Difference In Cadmium Accumulation Characteristics Of Detached Rice Organs

Cadmium（Cd）is one of the heavy metals with strong biological toxicity and exists in soil for a long time.Under acidic conditions,rice vegetative organs are prone to accumulate a large amount of Cd,and transport part of Cd to grains.These Cd-contaminated rice may be consumed by human beings,thus produce a potential threat to human health.There are significant differences in cadmium absorption and accumulation among different rice germplasm resources.The establishment of early and rapid screening technology for low cadmium accumulation characteristics is helpful to screen stable low cadmium accumulation varieties from a large n umber of germplasm resources and improve the technical level of safe rice production in China.In this study,9 different rice genotypes were used as materials,and the genotypic difference in cadmium accumulation characteristics of detached organs and the reliability of rapid identification methods for low cadmium accumulation characteristics were analyzed through field,pot and detached organ tests.The main results are as follows:（1）Cadmium absorption rate and leaf chlorosis rate in detached leaves were s ignificantly different among the 9 genotypes.After detached leaves of 9 genotypes stressed in solution with Cd of 0.1-2.0 mg·kg^-1 for 12 hours,the average cadmium absorption rate of leaves was 0.83-5.35mg·kg^-1·h^-1.After stressed for 5 days,leaves of some genotypes completely lost green colour,and the average leaf chlorosis rate of detached leaves was 0.53-16.25 mg·kg^-1·h^-1.The cadmium absorption kinetics of detached leaves was well fitted by the Michaelis equation,and the maximum cadmium absorption rate Fmax of leaves was between 31-170nmol·kg^-1·h^-1.According to the cadmium absorption and leaf chlorosis characteristics of detached leaves,the leaves from different genotypes were divided into three types:cadmium sensitive,cadmium tolerant and high cadmium sensitive types.Tanzao 215 leaves represented cadmium sensitive type,which displayed obvious leaf chlorosis when the leaves were stressed by low content of cadmium.The leaves of Lucaihao,Zhenshan 97B and Fupin 36 represented cadmium tolerance type,which did not show obvious leaf chlorosis with the increase of cadmium content in them.The leaves of Erjiunan No.1 and Zhuzhen B represented cadmium-dependent type,which remained green when the cadmium content was low but showed obvious chlorosis when the cadmium concentration was high.（2）Cadmium accumulation rate of detached panicles showed significant differences among 9genotypes.According to the relationship between cadmium accumulation characteristics of detached panicles and environmental cadmium concentration,rice genotypes were divided into three types:stable high-Cd-accumulation type,stable low-Cd-accumulation type and Cd-dependent type.Cultivars of stable high-Cd-accumulation type（i.e.,Fupin 36 and Zhongzao 35）showed stable increase of Cd content in grains with the increase of Cd concentration in the environment,and the Cd accumulation in grains was very high under high Cd stress.Cultivars of stable low-Cd-accumulation type（i.e.,Zhenshan 97B and Tanzao215）had low Cd accumulation i n grains under the stress environment with differernt Cd concentrations.Cultivars of Cd-dependant type（i.e.,Tieganwu,Lucaihao,Erjiunan No.1,Chaoyang No.1 B and zhuzhen B）showed different response to Cd stress.Some cultivars like Tieganwu and Lucaihao showed low Cd content in grains when panicles were treated in solutions with low Cd concentrations,but displayed a gradual increase of Cd content in grains with the increase of Cd levels in solutions with high Cd concentrations.Some cultivars like Erjiunan No.1,Chaoyang No.1 B and Zhuzhen B showed a gradul increase of Cd content in grains with the increase of Cd levels in solutions with low Cd concentrations,while shoewed a stale Cd content in grains when their panicles were treated in different high Cd solutions.（3）Genotypes showed differences in Cd accumulation among rice organs and in Cd transfer factors（TF）between adjacent organs.Pot experiments were carried out in cadmium contaminated soil(Cd content was about 1.0 mg·kg^-1,p H was about 7.6).The cadmium accumulation of 9genotypes varied from 0.052 to 0.121 mg·kg^-1.Lucaihao had the lowest while Fupin 36 had the highest Cd content in grains.Cadmium content in rachises was highly and linearly related to cadmium content in rice grains,r=0.837.Chaoyang No.1 B showed the lowest while Fupin 36showed the highest Cd content in stalk base part.The transfer factor of cadmium from rachises to grains TF _rachis→grain was between 0.261 and 0.415.Lucaihao showed the lowest while Zhongzao 35showed the highest TF _rachis→grain.Both Zhongzao 35 and Fupin 36 had higher Cd content in organs and higher transfer factors between organs than other genotypes.Therefore,they weretypical of high-Cd-accumulation type.（4）The effects of cadmium on the accumulation of essential elements in detached panicles were significantly different among genotypes.The contents of Mn and Fe in grains of some genotypes（i.e.,Zhuzhen B and Lucaihao）increased with the increase of Cd content.The contents of Ca and Zn in grains of some genotypes（i.e.,Zhenshan 97B and Lucaihao）increased with the increase of Cd content.However,the contents of Mn,Fe and Zn in grains of the other genotype（i.e.,Erjiu Nan No.1）decreased with the increase of Cd content.Among the 9 genotypes,the concentrations of Cd,Mn,Ca and Fe in Zhenshan 97B grains were lower than those of other genotypes,which indicated that this genotype had lower efficiency for ion transport.