Uptake of Cd²⁺ and Fe²⁺ by excised roots of Tamarix aphylla

Abstract

The uptake of Cd2+ by excised roots of Tamarix aphylla (L.) Karst, was investigated using roots of hydroponically grown plants. The concentration isotherm of Cd2+ uptake approached saturation with a single phase hyperbola. The time course of Cd2+ absorption was generally hyperbolic, with an apparent linear section between 2 and 30 min. The temperature response varied among different temperature ranges: a Q10 of approximately 1.9 was found between 10 and 20°C, but at higher and lower temperatures Q10 values were only 1–1.3. It is concluded that Cd2+ uptake by the roots of T. aphylla at moderate temperatures is mediated by a metabolic process, combined with a passive influx component that becomes dominant at higher and lower temperatures. The distribution of the absorption sites for Cd2+ and for Fe2+ along the roots of T. aphylla was also investigated. Cadmium uptake showed no apparent pattern, whereas a distinct pattern of uptake was observed for Fe2+, with the highest rates at the root tip. Iron absorption was stimulated in the presence of nutrients, whereas that of Cd2+ was inhibited. Adsorption and absorption of Cd2+ were strongly inhibited by Ca2+ and by Mg2+, but were unaffected by Fe2+. Monovalent ions (Na+, K+, Li+) also reduced Cd2+ absorption, but to a lesser extent than Ca2+ and Mg2+. Uptake of Cd+ was reduced at lower pH of the medium. The importance of interfering cations for Cd2+ tolerance of T. aphylla is emphasized.

Alleviation of Cd Toxicity in Arabidopsis thaliana Seedlings by Exogenous Ca 2+ or K +

“…et al, 2005)。张旭红等(2006)研究表明, Cd诱导蚕豆(Vicia faba)叶片DNA损伤, 高浓度的Cd 胁迫甚至会导致DNA双链断裂。本研究采用一种检测 重金属污染影响植物遗传效应的快速而敏感的彗星 检测方法(Jiang et al, 2007), 研究结果表明, 各浓度Cd胁迫下, Ca 2+ >Mg 2+ >K + >Na + 。即化合价越高, 离子半径 越 大 , 抑 制 作 用 越 强(Hagemeyer and Waisel, 1989)。(2) Ca 2+ 通过稳定膜结构维持细胞内外的离子 平衡(汪洪等, 2001)。 (3) Ca不仅作为一种植物必需的 大量营养元素, 更重要的是作为胞内的第二信使, 启 动一系列生理生化过程, 激活植物体内的多种抗性机 制(孙大业等, 2001)。 已有研究表明, 胞质中Ca 2+ 浓度 添加K使得K + 浓度升高, 与Cd 2+ 竞争拟南芥根部的吸 附 位 点 , 从 而 影 响 植 物 对 Cd 2+ 的 吸 附 ( 宋 正 国 等 ,2009a); (2) 由于Cd处理造成根毛细胞膜的去极化, 抑制K + 内向通道活性, 诱导外向K + 通道开放, 导致根 系内K + 外渗, 引起植物必需的大量元素K的缺失((2005). 钙和钙调素拮抗剂对高温胁迫下茄 子幼苗抗氧化系统的影响.…”