The Effect Of Different Cadmium Levels On Morphology And Subcellular Distribution In Rice Root

In recent years, as a result of industrial activities,fertilization and waste disposal, pollution of cadmium in agricultural soils has becoming increasingly serious throughout the world. It affected the grain yield and quality safety of rice, and it was important adversity of rice.Root,as an important organs absorbing water and nutrients and synthesizing growth regulation,have a direct influence on plant aboveground. However,the research about the mechanism of enduring the cadmium in rice material root was little.Therefore,4 rice varieties with different descendiblity speciality and Cd uptake types of roots were used in this paper. A hydroponic experiment was carried out to study the genotypic difference in Cd uptake,subcellular distribution,morphological chatacteristics and antioxidant enzyme activity in rice root under different Cd levels. The tolerant mechanism of Cd in rice root was discussed. The main results were as follows:(1) Increased Cd level in the medium caused a significant increase of Cd concentration in all fractions of roots. For the four cultivars,most Cd was distributed in the cell wall or soluble, and little Cd in the organelle. The Cd proportions showed different changes because of different Cd concentrations. With the Cd increase in the solution nutrition,the Cd proportion in the organelle increased,and the change about Cd proportion of cell wall was opposite to the cell soluble. In different growth stages, Cd concentrations in fractions of roots in the tillering stage was: cell soluble > cell wall> organelle. But in the booting stage and filling stage, the highest Cd concentration was in the cell wall.then cell soluble.Cd concentration and proportion varied significantly among the 4 tested materials. In conclusion, the Cd subcellular distribution of Cd low absorption type rice can more evidently avoid Cd toxicity than Cd high absorption type. With the increased Cd levels and boosting of the growth stages,Cd concentration gradually transferred to the cell wall from cell soluble in all rice materials. The increase amplitudes of restorer line materials were larger, especially Mianhui725, which cell wall had relatively stronger capacity to store Cd.(2)Under the condition of 0.5 mg/L Cd treatment(T₁)root length,root volume and root amount of 4 rice varieties were significant increasing than the control. When Cd concentration was 1 mg/L(T₂),root was still keeping good growth,but worse than Ti. With the increase of Cd concentrations,the growth of rice root was restrained, root length,root volume and root amount minished markedly. It was shown that low and middle Cd concentrations accelerated the growth of rice roots,high Cd concentration restrained it. With the boosting of the growth stages,root growed gradually slowly. The absolute values of root modality were the tiptop in Filling stage,and the increase amplitudes were larger in Booting stage.Root modality varied significantly among the 4 tested cultivars. The root length,root volume and root amount of maintainer line YixiangB and E2B changed conformably. But under 3 mg/L (T₃) Cd concentration,Cd low absorption type E2B was relatively stable,and amplitude reduction was less. In all treatments, restorer line Mianhui725 showed better growth than Cd high absorption type R892,the former had developed root system,and amplitude reduction was less under high Cd treatment. Both Cd high absorption type and low absorption type, restorer line materials had relatively stronger capacity to anti-Cd than maintainer line materials,especially under high Cd treatment.(3) With the increase of Cd concentrations, SOD,APX activity in rice roots increased in the low concentrations and reduced in the high concentration. It was shown that low Cd concentration accelerated the SOD,APX activities,high Cd concentration restrained itSOD activity varied with growth stage in the order of tillering stage>booting stage>filling stage,and APX activity varied in the order of booting stage > tillering stage > filling stage.The variation of rices reached significant at 0.05 probability level between different Cd levels. The SOD,APX activities of Cd low absorption type were pronounced higher,and E2B,Mianhui725 had small amplitude reduction under high Cd concentration. In the middle and later stages,the variation of rices were aggrandizement. The differences of SOD activity were not markedly of Cd high absorption type materials between maintainer line and restorer line in the tillering stage. The same rules of APX activity about them were under T₁ in the tillering stage. The SOD,APX activities of Cd low absorption type reach significant differences in three stages. In conclusion, restorer line had stronger capacity to anti-Cd than maintainer line. Especially Mianhui725,it showed stronger capacity to anti-Cd.