大豆初生根凯氏带对铜离子的通透性

Permeability of Endodermal Casparian Bands for Cu^(2+) in Primary Roots of Soybean (Glycine max)

采用在根内生成有色铜沉淀的方法研究大豆(Glycine max)初生根凯氏带对铜离子的通透性。用真空泵抽取浓度为200μmol·L–1的CuSO4溶液进入根中,然后在重力作用下从根基部灌注400μmol·L–1的K4[Fe(CN)6]溶液,两种物质在根内相遇即可产生棕色的Cu2[Fe(CN)6]沉淀,根据沉淀的位置来确定铜离子所经过的途径。结果表明:Cu2+可以穿过内皮层凯氏带,在木质部导管壁以及凯氏带至木质部之间的细胞壁处产生棕色沉淀,侧根发生的部位也产生了大量的沉淀;当抽取K4[Fe(CN)6]溶液后再灌注CuSO4溶液,发现Cu2+仍然可以穿过凯氏带,并在凯氏带外侧以及外皮层细胞的细胞壁处产生棕色沉淀。研究结果证明凯氏带并不是一个可以完全阻止离子进出的完美屏障。

Using a technique of insoluble salt precipitation, we investigated the permeability of endodermal Casparian bands （CBs） for Cu^2＋ in primary roots of soybean （Glycine max L. cv Nongda 5828）. Insoluble brown crystals of Cu ferrocyanide, indicating passage of Cu^2＋, were observed after 200 μmol·L^–1 CuSO4 was sucked into the root from its medium by use of a pump and subsequent perfusion of xylem with 400 μmol·L^–1 K4[Fe（CN）6]. Under suction, Cu^2＋ could cross the endodermis apoplastically in soybean, with brown salt precipitates in cell walls of xylem and in the region between CBs and xylem vessels. Regions where laterals penetrated the endodermis showed brown salt precipitates as well. When sides of CuSO4 and K4[Fe（CN）6] application were reversed, Cu^2＋ could still cross the CBs and induce brown salt precipitates outside CBs and cell walls of exoderm cells. The results suggest that CBs are not perfect barriers to apoplastic ion flux.