Cadmium Accumulation And Physiological Effects Of Cadmium Stress In Different Rice Varieties

Cadmium(Cd)pollution is the most serious pollution of heavy metal in China.For the increasing demand of food and environmental protection,breeding new rice varieties with high yield,high quality and low accumulation of cadmium has become one of the most economic means to reduce the risk of rice cadmium exceeding.In order to study the differences in cadmium accumulation between indica and japonica rice,and screen germplasm resources with low cadmium accumulation and strong cadmium tolerance,experiments which investigated the differences in cadmium absorption,translocation,accumulation and physiological effects of cadmium tolerance among different rice varieties were performed.And the results are as follows:1.In order to find out the differences in cadmium accumulation and translocation ability of different rice varieties under cadmium stress,we selected 40 rice varieties which are mainly-planted cultivars in Guangdong Province,and planted them in both paddy field and hydroponic conditon.By meansuring the cadmium content in the brown rice under paddy field condition,we finded out that the content of cadmium in brown rice of indica rice was significantly higher than it in japonica rice.And according to the level of cadmium in brown rice,the 40 varieties were divided into 6 categories from I to VI with the order from high to low.The cadmium translocation factor and partition factor of shoot at seedling stage and field tillering stage were significantly different among the categories.The cadmium translocation factor of plant shoot at seedling stage under hydroponic condition were positively correlated with it at tillering stage under paddy field conditon.While the cadmium accumulation and transport characteristics were similar under the two conditions.Based on our result,we found out a low cadmium accumulation rice variety named Guanghong 3.In the two-season field trial,17 major rice varieties had higher grain cadmium content in the late season than that in the early season.2.12 representative rice varieties(2 japonica conventional rice,4 indica hybrid rice and 6 indica conventional rice)were selected for hydroponics experiment at the cadmium concentrations of 0,25 and 100 μM respectively.By analyzing the plant phenotypic indexes,physiological and biochemical indexes and heavy metal content of each rice type to study the phenotypic and physiological effects of each rice type under cadmium stress.The results showed that the cadmium stress had significant inhibitory effects on plant height,shoot fresh weight,and shoot dry weight in all types of rice.The inhibitory effects showed obviously differences among the genotypes.It was from strong to weak in the order of indica hybrid rice > japonica conventional rice > indica conventional rice.Cadmium stress decreased the SOD activity and CAT activity of various types of rice shoot and root.It also increased the POD activity and the MDA content of shoot and decreased the soluble protein content.The content of cadmium in shoot,root,translocation factor and partition factor in each type of rice all increased with the increase of cadmium stress concentration,while the content of iron in shoot,translocation factor and partition factor decreased first and then remained stable with the increase of cadmium stress concentration.The translocation of cadmium and iron showed significant competitive effect.The cadmium accumulation ability of japonica rice seedlings was stronger than that of indica rice,and its cadmium transport efficiency was different in two stress concentrations.There are significant differences of the phenotypic and physiological effects among rice seedlings of 12 varieties under cadmium stress.Compared with all the data in seedling stage,Guanghong 3 has the strongest cadmium tolerance.