Study On The Absorption Of Heavy Metals By Roots Of Different Rice Varieties

Heavy metal pollution of soil is directly related to the food safety human beings and in recent years, therefore, already become one of the hot tops in the field of environment. In China rice is the most important grain crop. The rice plant grown in the heavy metals contaminated soil can absorb heavy metals by root and enriched them in grain. Through food chain by human consumption the heavy metals could be accumulated in human body. The absorption efficiency of different rice varieties to heavy metals is different, which suggest that we should search for the inherent reasons of such phenomenon from the genetic and physiological characteristics of rice root system. In the present study 3 rice varieties including Yangdao 6 (Indica), Huaidao5 (Japonica) and Nipponbare (Japonica) and 3 metals including Cd, Cr and Cu were taken as test materials. With the help of hydroponic culture and root analyzer the relationship between the metal absorption of rice seedling and root structures of 3 varieties were studied. By non-damage micro-measurement technology (NMT) we tested the Cd2+ absorption rates at different points on the root surface, and analyzed the relationship between absorption rates at different points and the corresponding internal structure of roots. With Electron Microscopy the distribution of Cd2+ in the root cross section of rice seedling was speculated. The main results are as follows:(1) The biomass of whole plant and root biomass of Yangdao 6 (Indica) were larger than those of Huaidao5 (Japonica) and Nipponbare (Japonica).(2) The root length, root surface, whole volume and average diameter of Yangdao 6 were significantly greater than those of Huaidao 5 and Nipponbare. The root tip number of Yangdao 6, however, was the smallest, implying a stronger ability of branching roots.(3) Under lower concentrations of metals, the differences in absorption rate between rice varieties were not significant, with increasing concentration the difference was more and more obvious.(4) When comparing the heavy metal absorption capacity of different rice varieties it’s likely to get a different order if the different root structure elements were taken as computational unit.(5) During the development of rice root a layer of thick-wall fibrous cell were formed in the cortex, which had a blocking effect on ion absorption. The cadmium absorption rate of both Indica and Japonica at root tips was the biggest, followed by the root hair zone, and the zone between root tip and root hair had the Minimum absorption rate.(6) The cadmium uptake rate of Indica was two times higher than that of Japonica, either at root tip or in root hair zone.(7) based on the results obtained it can be inferred that the number of cadmium transport channels in unit root surface of Nipponbare(Japonica) is more than that of Yangdao 6(Indica), the cadmium transfer efficiency of single channel, however, was less than that of Yangdao 6 (Indica).