Study On Screening For Cadmium-safe Rice Lines And Its Physiological Mechanism

Heavy metal pollution has been one of the problems those affect food security and threat to human health, thus, a low investment, low risk and effective method for food production is needed. Based on the serious Cd pollution situation, the concept of CSCs has been in in-depth explored. Present in the study, variation of Cd tolerance and Cd uptake among146Chinese rice lines totally were detected by a hydroponics experiment, and Cd low-uptake rice lines were acquired by testing whether Cd contents of brown rice were below the maximum permissible concentration (MPC) of standard of NFHSC (0.2mg kg-1) in the followed soil culture. Finally, physiological tolerance to Cd of Cd-safe rice lines was confirmed in the last hydroponics experiment. The main results are as follow:(1) Cd tolerance and Cd absorption were significantly varied among146rice lines under1mg L-1Cd stress, differences of Cd contents of113restorer lines and33maintainer lines were2.79-fold and2.00-fold in most as well as6.45times and2.98times when representing to Cd accumulation. However, no difference of Cd tolerance and Cd accumulation between the two rice types (restorer line and maintainer line) was detected. Thereby,9cultivars of low Cd absorption of restorer lines and6cultivars of maintainer lines were distinguished under dynamic clustering analysis by using Cd tolerance indices and Cd concentration as indicators, they were Lu5278-I332、R9113、 Lu17-T21712、Lu17-1R199、Luhui602、Lu5274-1332、Lu17-I2R16、Luhui17、 R527-M63(restorer lines) and DiguB、IRBN95-90、D26B、Xiang2B、Mian5B、 KangfengB (maintainer lines).(2) Whether under2mg kg-1or10mg kg-1Cd stress, variation of biomass, Cd content and Cd accumulation in roots, stems, leaves and grains of rice lines at tillering stage and maturity stage were detected to be both cultivar and Cd level dependent, and Cd distribution were decreased progressively in each organs. Cd contents in brown rice were in the range of0.028-0.386mg kg-1(2mg kg-1) and0.073-0.962mg kg-1(10mg kg-1). By taking NFHSC as standard, CSCs of rice lines were detected from the tested rice lines and they were Lu5278-I332、Lu17-T21712、Lul7-I2R60(restorer lines) and IRBN95-90、D26B (maintainer lines).(3) Root biomass, total root length, root surface area and root volume of CSCs were promoted under0.5mg L-1Cd stress and low diameter roots (<1.0mm) were in a large proportion which is benefit to increase metabolic capacity of roots. Under higher Cd treatments, roots of Lu5278-I332were slightly inhibited not as well as Luhuil7both at seedling stage and tillering stage, furthermore, roots with higher diameter (>1.5mm) were relatively and significantly increased when compared with Luhui17, it might promote material transportation and energy conversion in roots, which indicated the highly Cd tolerance in roots of CSCs.2) Photosynthetic superiority was explored in CSCs whether under short-term or long-term Cd duress. Biomass, SPAD, Ci and Pn in leaf of Lu5278-I332were higher than Luhuil7, and the variable trend of Ci and Gs indicated that Lu5278-1332’s leaf was relatively and more slightly damaged and its Cd tolerance in leaf was confirmed.3) MDA contents of root and leaf in Lu5278-I332were maintained at a low level and its membrane lipids were slightly damaged. SOD, POD and CAT activities of Lu5278-I332varied regularly due to Cd pollution level, and they were steadily higher than those of Luhuil7, which symbolized the highly ability of physiological regulation of CSCs.