Analysis On The Genetic Differences Of Cadmium Accumulation Characteristics And Their Stability In Rice

With the rapid development of modern industrial and agricultural productions,more and more industrial “three wastes” are being discharged into environment.The area of Cadmium（Cd）polluted farmland is continuously expanding,which threatens the safety of rice production increasingly.Screening and breeding low-Cd-accumulation cultivars,is one of the effective ways to decrease the risk of rice production safety in middle and mild Cd contamination field.Study on the mechanism of Cd uptake,accumulation and translocation in rice,will do some help to breeding low-Cd-accumulation cultivars,and furthermore offering some theoretical basis for controlling Cd concentration in grains.Core rice germplasms and main cultivars of current plantation were used to study the Cd accumulation characteristics among different genotypes and analyze their stability based on laboratory test and field test.The difference in Cd subcellular distribution and concentration of non-protein thiol compound between genotypes were compared.At the same time,the relationships between Cd accumulation in seedling roots and Cd translocation ratio,Cd tolerance of detached leaves and Cd accumulation characteristics in rice were explored.The main results were as follows:1.The maximum Cd accumulation rate and translocation ratio from roots to shoots were significantly different among genotypes.The Cd absorption kinetic characteristics of roots in rice seedlings were well described by Michaelis-Menten equation.The above-ground Cd accumulation kinetic characteristics was well fitted by a linear equation when root F_max was lower than 50.8 nmol·g^-1·h^-1 in 13 rice varieties.The Cd transport efficiency of these rice varieties was raised with the increase of Cd concentration in the environment.The above-ground Cd accumulation kinetic characteristics was also well fitted by Michaelis-Menten equation when the root F_max was higher than 55.5 nmol·g^-1·h^-1.But the Cd transport efficiency of these rice varieties was increased firstly and then decreased with the increase of Cd concentration in the environment.2.The stability of Cd accumulation in roots and above-ground of rice seedling was analyzed.The results showed that,genotype,environment and interaction between these two factors had significant influence on Cd accumulation of rice.‘Qitoubaigu’ and‘Guangliangyou 1128’ were the varieties with high and stable Cd content in rice seedlings.‘Mamagu’,‘Teqingxuanhui’ and‘27760’were the varieties with low and stable Cd content in rice seedlings.3.The Cd absorption kinetic characteristics in root cell walls and protoplasts were well described by Michaelis-Menten equations.The maximum Cd absorption rate F_max of ‘Qitoubaigu’ was significantly greater than that of ‘27760’,while Km values between them were no significant difference.The Cd absorption rates in cell walls and protoplasts of above-ground parts were linearly increased with the Cd concentrations in soluble fractions of root cells.‘Qitoubaigu’ showed significantly higher Cd accumulation rates in cell walls and protoplasts of aboveground parts than ‘27760’ when their Cd concentrations in soluble fractions of root cells were same.The Cd in soluble fractions of root cells is the direct source of aboveground.4.The Cd in rice roots mainly allocated in cell walls,followed by cellular soluble fractions,and only a few in the organelles.The subcellular distribution of Cd in rice above-ground parts followed the order: cell walls>> cellular soluble fractions> organelles.The distribution of Cd in cell walls and cellular soluble fractions had no significant difference between different varieties,while the distribution of Cd in organelles of ‘27760’ was significantly lower than that of ‘Qitoubaigu’.The contents of non-protein thiols in both roots and shoots of ‘27760’ were greater than that of ‘Qitoubaigu’.PC2 and PC3 were mainly existed in roots,but GSH and Cys mainly in above-ground parts.5.With the increasing of Cd concentration,the detached leaves of ‘Qitoubaigu’ displayed lower chlorophyll decreasing speed than that of ‘27760’ when the detached leaves were maintained in Cd concentrations varied from 0.89 μmol·L^-1 to 8.9 μmol·L^-1.The Cd tolerance of rice detached leavies was closely associated with the Cd accumulation in seedling roots and Cd transport efficiency from roots to shoots.These physiological traits can be used for fast identifying low-Cd-accumulation varieties.6.The field trials were carried out in the soil with Cd content of 1.782 mg·kg^-1 and pH 5.2,the rate of Cd surpassed the official maximum allowable limit in rice was up to 98.7%.The maximum of Cd content in rice grains was 2.049 mg·kg^-1,the minimum was 0.197 mg·kg^-1.After comprehensive analysis on the Cd absorption characteristics of rice seedling,decreasing speed of chlorophyll in detached leaves and the result of field trials,we found that ‘Shanjiugu’ and ‘Guihuahuang’ were the low-Cd-accumulation varieties with high Cd sensitivity,and ‘Qitoubaigu’ and ‘Jing7623’ were the high-Cd-accumulation varieties with high Cd tolerance.