| Rice is the first food crop and about60%of population with it as the stable food in China. Rice cadmium pollution is becoming more and more serious, and has threatened the human health seriously. Therefore, it is very important for researching rice cadmium pollution. In this study, the effect of cadmium on the growth and development, physiological activity and their differences were investigated with the different genotypes rice in all stages. Moreover, the methods to regulate cadmium toxicity and absorption were researched. The main results are as follows:1Characteristic of cadmium accumulation and differences in different genotypes riceAn experiment was set to research the different characters of cadmium absorption and accumulation between different genotypes rice in potted condition, with Xiushui63, Yongyou8, Yangdao6, Liangyoupeijiu and Shanyou63et al five different genotypes rice. The results showed that cadmium absorption capacities were different in different growth stage and genotypes rice, the content of cadmium in rice plant reduced gradually with development of rice. Cadmium concentration in grain, leaf and stem were significant difference between different genotypes rice, and increased dramatically with addition of soil cadmium concentration. In this study, cadmium content in grain of Xiushui63was only0.17mg-kg-1when the cadmium concentration of soil was more than5mg-kg-1, which under the limit value (0.2mg-kg-1) by the national standard, others exceed standard limit, but only little. Therefore, it is feasible for screening and cultivating rice variety which the grain accumulation lower cadmium. Abilities of enrich cadmium in grain were significant diversity, Yongyou8was the strangest and Xiushui63was the weakest. They were affected by soil cadmium concentration, which were stranger in low cadmium than high cadmium. The capacities of cadmium transport were influenced by soil cadmium concentration and genotypes interaction. Correlation analysis indicated that there were significant or extremely significant correlations in cadmium content of grain and each growth stage. The correlation coefficients were difference between different genotype rice, which showed that the contributions of cadmium absorption at different growth stage to grain cadmium accumulation were different between genotypes rice. The correlations of cadmium content among stem, leaf and grain were significant or extremely significant in all rice.2Effect of cadmium on growth and absorption of nutrition elements in different genotypes riceA pot experiment was conducted to research the effect of cadmium on growth and absorption of Ca, Mg, P, K. Cadmium was added into soil to form two levels, i.e.0(CK) and25mg-kg-1(Cd tolerance), with Xiushui63, Yongyou8, Yangdao6, Liangyoupeijiu and Shanyou63et al five different genotypes rice. The results showed that the yield, panicle number, filled spikelet rate were reduced significantly under cadmium stress, but the reduction of grain weight was not significant. Rice dry matter production was restrained by cadmium and weakened gradually with growing process. There was difference in affecting by cadmium between different genotype rice. The growth of Shangyou63and Xiushui63affected by cadmium were less, which indicated their resistances to cadmium were strong. The growth of Liangyoupeijiu, Yongyou8and Yangdao6affected by cadmium were more, which indicated their resistances to cadmium were weak. The result also indicated that the affect of cadmium stress on mineral nutrient concentrations in shoot differed types and mineral nutrients. When exposed to cadmium stress, reduced effect could be noted for K, P and Mg, thus resulting in reduced concentration. On the other hand, increased effect was found for Ca. It was not only affected rice absorbing Ca, Mg, P and K, but also affect its distribution and accumulation on the organs of ground parts under cadmium stress, which existed difference between different genotypes rice. Compared with CK, the Ca content in cadmium resistence strong varieties increased larger than resistence weak, but not in Mg, P and K. This indicated that maybe there was a relationship in cadmium resistence and calcium metabolism.3Research on differences of photosynthetic characteristics, antioxidant and Nitrogen metabolism enzymes in different resistence rice under cadmium stressAn experiment was set to research the responses and differences of photosynthetic characters, antioxidants and nitrogen metabolism enzymes activities under cadmium stress in different growth stage with different cadmium resisitence rice varieties. The results indicated that photosynthetic rate was restrained by cadmium and the extent of inhibition reduced following development of rice. The extents of restrain in resistance varieties were lower than sensitive. Stomatal conductance, intercellular CO2concentration and transpiration rate had the similar performance. Cadmium lead to membrane lipid peroxidat more severe which promoted MDA content increased, and cadmium sensitivity varieties increased more than resistance varieties. The activities of antioxidant enzymes were promoted by cadmium such as SOD, CAT and POD, which resistance promoted more than sensitive. Compared with CK, SOD and CAT activity increased more significant in tillering and jointing stage than in heading and filling stage, and POD activity was opposite. Nitrogen metabolism enzymes activities were also affected by cadmium. Compared with CK, nitrate reductases activities were restrained in tillering and jointing stages but were promoted in heading and filling stage under cadmium stress. Glutamine synthetases activities were inhabited in whole growth period. Glutamic oxalacetic and glutamic-pyruvic transaminases were inhabited in early and medium stage and promoted in later stage. Compared with sensitive varieties, the inhibitions of nitrogen metabolism enzymes activities in resistance varieties by cadmium were less and promotion were more. In conclusion, the rice resistance to cadmium stress may have relation with photosynthesis, antioxidants and nitrogen metabolism enzymes activities.4Differences of subcelluar distribution and chemical forms in different cadmium resistence riceA soil culture experiment combined with the method of soucrose differential centrifugation and chemical reagent stepped extraction was carried out to research the subcellular distribution and chemical forms of cadmium and change with growth development in rice leaves, and the differences between cadmium resistive and sensitive rice varieties were compared. The results showed that with rice growing, the cadmium content in all fractions of rice leaves reduced, and most of cadmium accumulated in cell wall and soluble substance. Compared with sensitive varieties, resistive varieties had significant higher cell wall and soluble fraction of cadmium and significant lower organelle fraction of cadmium in leaves, especially at early stage. The greatest amount of cadmium in leaves was in the extraction solution of NaCl, followed HAC and HCl, ethanol and water were lower. Concentration and percent distribution of cadmium in different extractions would change at different growth stage. Compared with sensitive varieties, cadmium content and distribution in ethanol and water extraction, which had stronger mobile activity, of resistive varieties were lower, and the extraction which difficult to move were higher. This performance was particularly significant at early stage. Therefore, the capacities of rice resistance to cadmium have relation with the subcellular distribution and chemical forms of cadmium in rice. The study also found that high cadmium content in grain may have relationship with the higher soluble fraction and mobility stronger extraction in rice in filling stage.5Effect on cadmium tolerance and absorption in two cadmium accumulation rice types by siliconThe alleviation effect of silicon on cadmium toxicity to rice plants was investigated using a hydroponic experiment with three cadmium levels, two silicon levels and two different cadmium accumulated rice types. The result indicated that the inhibition were greatly alleviated due to silicon addition to the culture in low cadmium treatment but no significant in high. The alleviated effect in Shangyou63was better than Wuyujing3. Compared with the plant treated with cadmium alone, silicon addition markedly increased praline content and SOD and CAT activities, reduced MDA content, which was better in Shangyou63than Wuyujing3, in low cadmium treatment and the function declined in high cadmium treatment. The cadmium content and percent distribution of cell wall was increased and the content and percent distribution of soluble and organelle were reduced by silicon addition. Moreover, by addition silicon, on one hand, the content and percent distribution of the extractions, which had stronger mobile activity, were reduced. On other hand the extractions, which were difficult to move, were increased. This effect which in low cadmium treatment was better than high treatment and Shangyou63was better than Wuyujing3. In conclusion, silicon alleviated the cadmium toxicity may through enhancing the capacity of defense against oxidative stress and reducing absorption and transportation. There were differences in that alleviation between different varieties, the high cadmium accumulated varieties was better than low.6Effect of wheat straw on cadmium remove in rice-soil systemThe experiment of rice cultivated in sandy and clay soil columns were conducted under outdoor condition to investigate the effects of wheat straw on cadmium remove in rice-soil systems in artificial cadmium-contaminated soils. The results indicated that cadmium content of rice reduced gradually with growth development. Addition wheat straw promoted rice to absorbing cadmium and increasing content of overground organs which were significant in grain and stem. Compared with Cd treatment, addition wheat residue led to increasing contents of cadmium availability significantly which was greater in caly than in sandy soil. Wheat straw promoted the cadmium transporting into grain and increasing the concentration factor. Compared with Cd treatment, the concentration factor increased50.0%and61.5%in sandy and clay soils by adding straw, respectively. Cadmium entered into soil and removed downward with water flow and the cadmium migrated ability in sandy was greater than clay. With soil depth increasing, cadmium content became less and less. Wheat straw reduced the cadmium migrated ability which in clay soil was greater than in sandy soil. In conclusion, wheat straw in cadmium contamination soil promoted cadmium migrating up, but restrained migrating down.7Accumulation of cadmium in japonica rice varieties with different growth period typesThe experiment was set to investigate the accumulation characteristics of cadmium in rice of different growth types in cadmium pollution farmland, with early-(125-135d), medium-(136-145d), and late-maturing (146-155d) medium japonica as well as early-(156-165d) and medium-maturing (166-175d) late japonica varieties. The result showed that the range of grain Cadmium content was0.014-0.054mg-kg-1for56rice varieties. The content of cadmium in grain showed significant variances among rice varieties, the highest variety are ELTO, the lowest varieties were Yangjing687, Siyang1382, Guanglingxiangjing and Wuxiangjing9. There was also difference in the content of cadmium of rice among different growth types. The content of cadmium in grain of early-maturing medium japonica was the highest and medium-maturing medium japonica was the lowest, were0.024and0.020mg-kg-1respectively. Concentration factor and transference coefficient were the important characteristic indexes in screening the low cadmium accumulating varieties of rice. In this research, the accumulation factors were different but not significant among different growth types rice. The transference coefficient showed significant difference among different growth types rice. |
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