持续淹水对水稻镉吸收的影响及其调控机理

【目的】研究持续淹水对不同镉(Cadmium,Cd)积累水稻品种Cd含量的影响,通过分析持续淹水条件下土壤有效性Cd、植株Cd含量以及水稻根系Cd吸收转运关键基因表达,揭示持续淹水对水稻Cd积累的作用及其调控机制。【方法】采用水稻品种辐品36(FP36,Cd高积累品种)和中嘉早17(ZJZ17,Cd低积累品种),盆栽条件下(外源加入1.5 mg·kg-1 Cd Cl2)于水稻分蘖始期开始持续淹水处理,分蘖盛期取样分析植株Cd含量及Cd转运相关基因表达情况,测定土壤中有效性Cd、Fe、Mn含量和根膜Cd、Fe和Mn含量。相同处理继续培养至水稻完熟期,收获植株和稻米并测定Cd含量和产量。【结果】在Cd污染土壤条件下,与正常灌溉处理相比,持续淹水显著降低了分蘖盛期水稻FP36和ZJZ17的Cd含量,根部降幅分别为39.5%和33.9%,地上部降幅分别为62.1%和71.7%。在完熟期也表现相同作用效果,持续淹水显著降低完熟期水稻FP36和ZJZ17根部、地上部和稻米中Cd含量,FP36根部、地上部和稻米分别降低36.4%、43.7%和36.8%,ZJZ17分别降低62.5%、61.5%和55.4%。研究发现,持续淹水显著降低了两个水稻品种的土壤有效性Cd含量(降幅分别为12.1%和17.7%)和根膜中Cd的含量(降幅分别为52.2%和43.1%)。Cd胁迫下,持续淹水增加了土壤有效性Fe(增幅分别为23.7%和10.3%)和有效性Mn含量(增幅分别为24.5%和43.9%),也使根膜中Fe(增幅分别为83.1%和81.5%)和Mn含量(增幅分别为41.5%和27.7%)显著增加。更为重要的是,持续淹水显著下调了两个水稻品种根部Os Nramp1(58.3%和58.0%)和Os LCD(21.6%和17.8%)基因的相对表达量。【结论】持续淹水通过降低土壤有效性Cd含量和抑制Cd吸收基因表达(Os Nramp1和Os LCD)的双重调控作用,降低了水稻对Cd的吸收和积累。

Effects of Continuous Flooding on Cadmium Absorption and Its Regulation Mechanisms in Rice

【Objective】The objective of this experiment is to study the effects of continuous flooding on cadmium (Cd) uptake in rice. By analysis of alteration of soil available Cd, plant Cd content and Cd uptake related gene expression under continuous flooding condition in different Cd accumulation rice varieties, further to reveal the effects and detail regulation mechanism on Cd uptake with continuous flooding management in rice. 【Method】 Pot experiments (exogenous 1.5 mg·kg^-1CdCl₂ ) were carried out by using rice varieties of Fupin36 (FP36, high Cd accumulation) and Zhongjiazao 17 (ZJZ17, low Cd accumulation). Plantlets were treated by continuous flooding management at early tillering stage and sampled at middle tillering stage. Cd content of plant root and shoot, soil available Cd, Fe and Mn content, root plaque Cd, Fe and Mn content and Cd uptake related gene expression of rice were analyzed. The same treatment was continued until mature stage, plantlets and milled rice were harvested to determine Cd content and yield traits. 【Result】 Compared with the control, the results showed that continuous flooding sharply reduced Cd contents of FP36 and ZJZ17 under pollution condition at middle tillering stage, the root Cd content decreased by 39.5% and 33.9%, shoot Cd content decreased by 62.1% and 71.7%, respectively. Continuous flooding also significantly reduced Cd content of rice root, shoot and milled rice at mature stage. The management reduced root, shoot and milled rice Cd content of FP36 by 36.4%, 43.7% and 36.8%, respectively, it also showed a decrease of 62.5%, 61.5% and 55.4% in ZJZ17. Furthermore, the soil available Cd of FP36 and ZJZ17 significantly decreased by 12.1% and 17.7%, and root plaque Cd content decreased by 52.2% and 43.1% under continuous flooding treatment, respectively. While soil available Fe content (23.7% and 10.3%) and Mn content (24.5% and 43.9%) of FP36 and ZJZ17 significantly increased. Root plaque Fe (83.1% and 81.5%) and Mn content (41.5% and 27.7%) were also elevated under continuous flooding. Simultaneously, the relative expression of OsNramp1 (58.3% and 58.0%) and OsLCD (21.6% and 17.8%) genes were also down-regulated by continuous flooding in rice roots.【Conclusion】Continuous flooding decrease Cd uptake by decreasing soil available Cd content and down-regulating Cd uptake genes expression of OsNramp1 and OsLCD in rice.