| In current days, the soil polluted by heavy metal needs to be solved urgently, but the methods of its governance are still inadequate. To solve the sharp contradiction between the food security and slow control of soil pollution, the best method is to select crop varieties with low heavy metal accumulation, which could reduce the absorption and accumulation of heavy metal in crop and then reduce the heavy metal content in agricultural products. However, some questions of this method still needs to be explored. How about the suitability of the selected crop varieties under heavy metal stress? How much economic yield of the crop with low accumulation of heavy metal? Which one is the real reason for low accumulation in crop grain, less heavy metal uptaking by crop or less heavy metal migration to the grain of crop? In this study, we mainly focused on the uptake of cadmium（Cd） by winter wheat. A field plot experiment was carried out with 4 wheat varieties, including Luoyou9909, Xingmai6, Xinmai9817 and YaoMai16, to measure their agronomic characteristics and to verify the stability of their low accumulation characteristics. At the same time, a hydroponic experiment was conducted to measure the difference of root morphology, organic acid, non-protein thiol（NPT） in plant body and root exudates of these wheat varieties under Cd stress at 5100 μmol·L-1. We expected to provide the basis to reveal the mechanism of low accumulation in wheat by investigating the mechanism of low accumulation of wheat grain from these aspects. The main results are as follows:⑴ The effects of Cd stress on the root of wheat were investigated. The results showed that under the stress of different Cd concentrations, the root of Luoyou9909（low Cd accumulation variety） had higher biomass, and the root length, root surface area and root volume were higher than other cultivars under Cd stress at 5100 μmol·L-1. Correlation analysis was made between plant Cd accumulation and root morphological parameters, and the results showed that root morphology of Luoyou9909 was little affected by Cd stress, and Luoyou9909 had better root system and more biomass under Cd stress.⑵ The effects of Cd stress on the contents of organic acid in wheat plant and root exudates showed that the oxalic acid content in plant body and root exudates of low accumulation cultivars（Luoyou9909 and Yaomai16） was significantly higher than that in high accumulation cultivars（Xingmai6 and Xinmai9817） under Cd stress. Oxalic acid in plant body and root exudates were the key factors of root uptake and translocation to the shoots, and may be one of the key factors that cause the low accumulation of Cd in grain.⑶ The effects of Cd stress on the content of NPT in wheat plant and root exudates showed that the content of NPT in root exudates was related to the concentration of Cd stress. Under low concentration of Cd(5, 10μmol·L-1) stress, the NPT content in the root exudates of YaoMai16 was significantly higher than other varieties. While under high concentrations of Cd(20, 50, 100 μmol·L-1) stress, NPT content in root exudates of Luoyou9909 increased a lot. NPT in root exudates may be the key of root uptake of less Cd, the plant detoxification of Cd and the low accumulation of Cd in grain.⑷ The distribution of Cd in different wheat organs and production characteristics of wheat variety with low Cd accumulation were studied, and the results showed that: the Cd accumulation ability of low Cd accumulation variety was changed under different Cd concentration stresses. Based on the agronomic characters of wheat, it was found that the Cd contaminated soil that planted with Luoyou9909（low Cd accumulation variety） could effectively decrease the Cd content in grain, and the good economic yield was obtained under the same conditions. After 3 years of continuous cropping, the Cd content in grain of Yaomai16 and Luoyou9909 was more than 0.1 mg·kg-1. The low accumulation characteristics could be changed after multiple generations. |
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