Cd Stress On Root Morphological Characteristics And Anatomical Structure Of Rice Materials

With the rapid development of modern industry and agriculture, the Cd content in soil has increased. As a result, the problem about the Cd content in the soil-plant-food system has been more and more serious. Rice is the Cd-sensitive crop which is vulnerable to the impact of Cd, especially on the yield and quality. As the root directly contacted the contaminated soil, the morphological and anatomical structure of the plant have been changed. At present, there are many researches about the external morphology changes of rice which is under stress. However, the comparative study about the root morphological and anatomical structure of rice which is under Cd stress has not been reported. For this reason, in this experiment,4 maintain lines and restorer lines of rice breeding copies which are different in the genetic characteristics and root Cd accumulation capacity have been the test object. Through hydroponics experiment and paraffin sections, the difference of root morphological and anatomical structure from different rice materials has been compared. The injury characteristics of rice root anatomy under the Cd stress has been investigated. The research was designed to be the anatomical basis for the rice seed selection which kind is low absorption and low accumulation. The main findings are as follows:(1)With the increase of Cd concentration, Cd content of 4 rice root increased gradually, the different changes between materials and different treatments were significant. Under different Cd concentration, maintainer, restorer root Cd content of rice materials were high accumulation-type was significantly higher than the low accumulation-type materials, demonstrated their ability of high accumulation or low on the Cd accumulation characteristics, and with the increase of Cd concentration and the promoted of growth stage, the differences increased. On the whole, both as high or low accumulation-type of rice materials, the Cd content of the maintainer line was higher than the restorer line, and restorer line had stronger capacity of anti-Cd; all rice materials with the growth stages,Cd content of roots increased and the scale of rise decreased.(2)Morphological and anatomical traits values of rice root in different growth stages and Cd concentration reacted differently to Cd,varied among the 4 tested materials.Under low Cd level, root diameter, cortex thickness, central cylinder diameter, xylem vessel diameter, the number of large xylem vessel of maintainer, restorer root of rice materials were increased at different degrees compared to control;Under high Cd level, both of them decreased at different degrees compared to control.Both as the same line materials, rice root morphological and anatomical traits values of low accumulation-type were higher than the high accumulation-type(Indicated that the morphological and anatomical traits values was higher, less stressed by Cd, showed a more normal).It was indicated when compared with low accumulation-type, high accumulation-type was more stressed by Cd,the ability of adapt to Cd toxicity even worse,with weaker capacity of anti-Cd. From the same accumulation-type to Cd, both as high or low accumulation-type of rice materials, the rice root morphological and anatomical traits values of the maintainer line was lower than the restorer line. The increase and decrease range of the maintainer line was higher than the restorer line, stability was worse than the restorer line, and root of restorer line had a better adapt ability to Cd toxicity, its means had a stronger capacity of anti-Cd. From growth stages,the morphological and anatomical traits values of rice root was booting stage highest, filling stage the second, maturity stage the lowest, with the boosting of the growth stages, all parameters decreased gradually, root affected by Cd toxicity deepen gradually.(3)Morphological and anatomical structure of rice root in different growth stages and Cd concentration reacted differently to Cd,varied among the 4 tested materials.Take booting stage for example, under low Cd level, new root appeared in the cortex of maintainer line materials. Compared with the low accumulation-type E2B, the diameter of the new root of high accumulation-type Yixiang B was thicker, and the stain was deeper; under high Cd level, epidermal off, cortex damage and dark spots appeared in both materials. Compared with the low accumulation-type E2B, the phenomenon of epidermal off, cortex damage of high accumulation-type Yixiang B were more serious, and the dark spots were closer to central cylinder. It was indicated when compared with high accumulation-type Yixiang B, low accumulation-type E2B with stronger capacity of anti-Cd, was less stressed by Cd. New root appeared at cortex in both restorer line materials, but under low Cd level, for high accumulation-type of R892, there was one more root than low accumulation-type of Mianhui 725, and the root with thicker diameter was closer to the central cylinder; under high Cd level, cortex damage of high accumulation-type R892 were more serious than the low accumulation-type Mianhui 725, which indicated that low accumulation-type Mianhui 725 was less stressed by Cd and had stronger capacity of anti-Cd.Both as high accumulation type of rice materials, just new root appeared in cortex of restorer line material R892, but in maintainer line material YixiangB, not only did new root appeare, but also serious cortex damage and dark spots appeared. It was indicated that damage to root structure of restorer line material R892 was slighter than maintainer line material YixiangB, and R892 was less affected by Cd toxicity; both as low accumulation type of rice materials, there were one new root and some dark spots appeared in root cortex of maintainer line materials E2B, but for restorer line Mianhui 725, there was only one root near by epidermis, and no dark spot was discovered. It was indicated that the changes in anatomical structure of roots in restorer line Mianhui 725 was slighter than maintainer line E2B, and restorer line Mianhui 725 had better stability and stronger capacity of anti-Cd. Look from different growth stages,the root morphological and anatomical structure of filling stage and maturity stage had the similar rules to booting stage under Cd stress(Under high Cd level,the rice root damaged by Cd were more serious than it's under low Cd level; maintainer, restorer root of rice materials damage caused by Cd were high accumulation-type more serious than the low accumulation-type materials; both as high or low accumulation-type of rice materials, the damage caused by Cd of the maintainer line were more serious than the restorer line).The morphological and anatomical structure of rice root effected by Cd was maturity stage deepest, filling stage the second,booting stage the slightest, and root system of self-regulating capacity presented as filling stage>booting stage>maturity stage.