Physiological characterization of root Zn2+ absorption and translocation to shoots in Zn hyperaccumulator and nonaccumulator species of Thlaspi
Physiological characterization of root Zn2+ absorption and translocation to shoots in Zn hyperaccumulator and nonaccumulator species of Thlaspi
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DOI：
10.1104/pp.112.4.1715
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发表时间：
1996-12-01
期刊：
影响因子：
7.4
通讯作者：
Kochian, LV
中科院分区：
文献类型：
--
作者：
Lasat, MM;Baker, AJM;Kochian, LV
利用放射性示踪技术研究了Zn-65（2+）在超富集植物刺皮（Thlaspi caerulescens）和非富集植物刺皮（Thlaspi arvense）根部的流入和向茎部的转运。我们制定了一项方案，使我们能够量化通过根细胞质膜的单向Zn-65（2+）内流（在100 μ M ZnCl2 + 5 mM CaCl2溶液中进行20分钟的放射性吸收，然后进行15分钟的解吸）。两种Thlaspi中浓度依赖的Zn2+内流产生的非饱和动力学曲线可以分解为线性和饱和组分。线性动力学组分是解吸后留在根内的细胞壁结合的Zn2+，饱和组分是通过根-细胞质膜流入的Zn2+。这一饱和组分遵循Michaelis- menten动力学，红毛竹和黄毛竹具有相似的表观Michaelis常数值（分别为8 μ M和6 μ M）。然而，Zn2+在毛竹根细胞内的最大初流速是毛竹根细胞的4.5倍，表明根细胞对Zn2+的吸收增强是锌超积累的机制之一。96 h后，锌-65转运到白杨茎部的量是白杨茎部的10倍。这表明除了进入根同质外，运输部位也受到刺激。我们认为，虽然根内Zn2+的增加是一个重要的组成部分，但叶片细胞的质膜和细胞质间的运输也必须是T. caulescens Zn超积累的关键位点。
Radiotracer techniques were employed to characterize Zn-65(2+) influx into the root symplasm and translocation to the shoot in Thlaspi caerulescens, a Zn hyperaccumulator, and Thlaspi arvense, a nonaccumulator. A protocol was developed that allowed us to quantify unidirectional Zn-65(2+) influx across the root-cell plasma membrane (20 min of radioactive uptake followed by 15 min of desorption in a 100 mu M ZnCl2 + 5 mM CaCl2 solution). Concentration-dependent Zn2+ influx in both Thlaspi species yielded nonsaturating kinetic curves that could be resolved into linear and saturable components. The linear kinetic component was shown to be cell-wall-bound Zn2+ remaining in the root after desorption, and the saturable component was due to Zn2+ influx across the root-cell plasma membrane. This saturable component followed Michaelis-Menten kinetics, with similar apparent Michaelis constant values for T. caerulescens and T. arvense (8 and 6 mu M, respectively). However, the maximum initial velocity for Zn2+ influx in T. caerulescens root cells was 4.5-fold higher than for T. arvense, indicating that enhanced absorption into the root is one of the mechanisms involved in Zn hyperaccumulation. After 96 h 10-fold more Zn-65 was translocated to the shoot of T. caerulescens compared with T. arvense. This indicates that transport sites other than entry into the root symplasm are also stimulated in T. caerulescens. We suggest that although increased root Zn2+ influx is a significant component, transport across the plasma membrane and tonoplast of leaf cells must also be critical sites for Zn hyperaccumulation in T. caerulescens.