Abteilung Forstbotanik und Baumphysiologie, Büsgen-Institut, Georg-August Universität, Büsgenweg 2, 37077 Göttingen, Germany.
J Exp Bot. 2012 Feb;63(3):1413-21. doi: 10.1093/jxb/err384. Epub 2011 Dec 3.
Cadmium (Cd) is a phytotoxic heavy metal that causes rapid growth reduction. To investigate if Cd interferes with the metabolism of auxin, a major growth hormone in plants, poplars (Populus × canescens) expressing a heterologous GH3::GUS reporter gene were exposed to 50 μM Cd in hydroponic solutions. Growth, photosynthetic performance, lignification, peroxidase activity, auxin concentration, and GUS staining were determined in order to record the activities of GH3 enzymes in the stem apex, the elongation zone, wood in the zone of radial growth, and in roots. Cd-induced growth reductions were tissue-specific decreasing in the order: roots>wood>shoot elongation and leaf initiation, whereas Cd concentrations increased in the order: leaves<wood<roots. Cd almost abolished the GH3 signal in the stem apex but caused strong increases in the vascular system of roots as well as in parenchymatic cells in the xylem. These changes were accompanied by increases in lignin and peroxidase activities and decreases in auxin concentrations. Since GH3 enzymes remove auxin from the active pool by conjugation and act as mediators between growth and defence, our data suggest that Cd stress triggered increases in GH3 activities which, in turn, depleted auxin in wood and thereby shunted the metabolism to enhanced formation of lignin.
镉（Cd）是一种植物毒性重金属，会导致快速生长减少。为了研究镉是否干扰植物主要生长激素生长素的代谢，研究人员将表达异源 GH3::GUS 报告基因的杨树（Populus × canescens）暴露于水培溶液中的 50μM 镉中。为了记录茎尖、伸长区、径向生长区木材和根中 GH3 酶的活性，测定了生长、光合性能、木质化、过氧化物酶活性、生长素浓度和 GUS 染色。镉诱导的生长减少具有组织特异性，顺序为：根>木材>茎伸长和叶片起始，而镉浓度的增加顺序为：叶片<木材<根。镉几乎完全消除了茎尖的 GH3 信号，但导致根系血管系统以及木质部薄壁细胞中的 GH3 信号强烈增加。这些变化伴随着木质素和过氧化物酶活性的增加以及生长素浓度的降低。由于 GH3 酶通过共轭将生长素从活性池中去除，并作为生长和防御之间的中介，我们的数据表明，镉胁迫引发了 GH3 活性的增加，这反过来又耗尽了木材中的生长素，从而将代谢转向增强木质素的形成。
