| Recent years, heavy metal pollution, especially cadmium contamination, become more and more serious, which makes the safety of rice production concerned a great deal. We studied the interaction between Ca and Cd, and the effect of Ca on Cd subcellular distribution characteristics of rice seedlings with two rice varieties (T705and X24) with different Cd accumulation property. At the same time, we studied genotypic and environmental effects on characteristic of Cd accumulation and stability of Cd content in multi-location field trials based on rice cultivars with early and late maturity.The main results were as follows:1、The root of two varieties showed a rise-fall trend with the increase of Cd2+concentration. In other words, Cd has a dual character, low concentration promotes and high contration inhibits root growth. The Cd toxicity to rice roots was partially alleviated by adding Ca. Adding2mmol/L Ca into4.5μmol/L Cd solution, the root length of T705and X24increased by172.05%and273.63%, respectively, comparing with their root length under Cd stress without Ca.2、The rates of Cd absorption and transportion two cultivars were reduced significantly by adding Ca. Absorption process of Cd can be decribed by the Michaelis-Menten equation. After adding2mmol/L Ca2+, the Fmax of Cd influx in the root and shoot of T705decreased by26.20%and73.86%, in the root and shoot of X24by10.64%and32.83%, respectively, but Km slightly changed. Adding2mmol/L Ca2+in4.5μmol/L Cd2+solution also reduced the Cd transport rate in T705by40.90%and in X24by23.48%.3、The subcellular eanalysis showed that Cd in rice root mainly allocated in cellular soluble fraction, followed by cell wall and only a few in the organelles. However, the subcellular distribution of Cd in rice shoot lollowed cell wall>cellular soluble fraction>organelles. The Cd contents in all subcellular fractions of T705were higher than that of X24. Supplement of Ca can reduce the Cd content in cellular soluble fraction of root and cell wall, organelles of shoot. Cd content in cellular soluble fraction of root reduced by48.14%for T705and43.05%for X24after adding2mmol/L Ca into4.5μmol/L Cd solution.4、In multi-location field trials, we found that the Cd content in the rhizospheric soil of late rice was significantly higher than that of early rice. It indicates that the Cd content in topsoil can be influenced by seasons significantly. The Cd content in rice root and grain can be influenced by seasons and cultivars, and the ratio of Cd surpassing the official maximum allowable limit in late rice was significantly higher than that in early rice cultivars in the Cd contaminated sites. The Cd content of early rice T705was significantly higher than other genotype in all sites. The Cd content of late rice F263was significantly higher than other genotype in S3and S4.5、AMMI model was used to analyze interactions between genotype and environment on Cd content and stability in rice. Genotype, environment and interaction between these two factors had significant effect on Cd content of rice. Furthermore, genotype had a more significant effect on Cd content of early rice cultivars and environment had a dominant effect on Cd content of late rice cultivars.6、Assessment of Cd concentration in grains of early and late rice varieties as well as the variability in different experiment sites shown that early rice varieties including X24, Zhong-jiazaol7, X11, X6and Ⅱ-you819were potential low Cd accumulation varieties and had perfect genetic stability. Therefore, these varieties were suitable for widely grown either in a slight degree or relatively mild contaminated area. However, T-you705was a kind of high Cd accumulation variety with great environmental variation. Such kind of genotype is not suitable for widely application in low contaminated area. Other cultivars can be suitable planted in low contaminated area. Among the late varieties, only F2297was suitable for widely grown in a slight degree contaminated area. |
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