Küpper Hendrik, Mijovilovich Ana, Meyer-Klaucke Wolfram, Kroneck Peter M H
Universität Konstanz, Mathematisch-Naturwissenschaftliche Sektion, Fachbereich Biologie, Postfach M665, D-78457 Konstanz, Germany.
Plant Physiol. 2004 Feb;134(2):748-57. doi: 10.1104/pp.103.032953.
Extended x-ray absorption fine structure measurements were performed on frozen hydrated samples of the cadmium (Cd)/zinc (Zn) hyperaccumulator Thlaspi caerulescens (Ganges ecotype) after 6 months of Zn(2+) treatment with and without addition of Cd(2+). Ligands depended on the metal and the function and age of the plant tissue. In mature and senescent leaves, oxygen ligands dominated. This result combined with earlier knowledge about metal compartmentation indicates that the plants prefer to detoxify hyperaccumulated metals by pumping them into vacuoles rather than to synthesize metal specific ligands. In young and mature tissues (leaves, petioles, and stems), a higher percentage of Cd was bound by sulfur (S) ligands (e.g. phytochelatins) than in senescent tissues. This may indicate that young tissues require strong ligands for metal detoxification in addition to the detoxification by sequestration in the epidermal vacuoles. Alternatively, it may reflect the known smaller proportion of epidermal metal sequestration in younger tissues, combined with a constant and high proportion of S ligands in the mesophyll. In stems, a higher proportion of Cd was coordinated by S ligands and of Zn by histidine, compared with leaves of the same age. This may suggest that metals are transported as stable complexes or that the vacuolar oxygen coordination of the metals is, like in leaves, mainly found in the epidermis. The epidermis constitutes a larger percentage of the total volume in leaves than in stems and petioles. Zn-S interaction was never observed, confirming earlier results that S ligands are not involved in Zn resistance of hyperaccumulator plants.
在用和不用添加镉离子（Cd²⁺）的情况下，对经过6个月锌离子（Zn²⁺）处理的镉（Cd）/锌（Zn）超积累植物天蓝遏蓝菜（恒河生态型）的冷冻水合样本进行了扩展X射线吸收精细结构测量。配体取决于金属以及植物组织的功能和年龄。在成熟叶和衰老叶中，氧配体占主导。这一结果与早期关于金属区室化的知识相结合表明，植物更倾向于通过将超积累的金属泵入液泡来解毒，而不是合成金属特异性配体。在幼嫩和成熟组织（叶、叶柄和茎）中，与衰老组织相比，更多比例的镉由硫（S）配体（如植物螯合肽）结合。这可能表明，幼嫩组织除了通过在表皮液泡中隔离来解毒外，还需要强配体来进行金属解毒。或者，这可能反映了已知的幼嫩组织中表皮金属隔离比例较小，再加上叶肉中S配体的比例恒定且较高。与同一年龄的叶片相比，在茎中，更高比例的镉由S配体配位，锌由组氨酸配位。这可能表明金属是以稳定的复合物形式运输，或者金属在液泡中的氧配位，就像在叶片中一样，主要存在于表皮中。表皮在叶片总体积中所占的百分比比在茎和叶柄中更大。从未观察到锌 - 硫相互作用，这证实了早期的结果，即S配体不参与超积累植物对锌的抗性。
