黄芪幼苗对镉胁迫的生理响应机制

以我国传统药用植物黄芪(Astragalus membranaceus(Fisch.)Bunge)幼苗为材料,在水培条件下系统研究了不同程度Cd胁迫对黄芪生长发育、矿质元素吸收转运以及次生代谢产物积累的影响。25~200μmol·L^-1Cd处理显著抑制了黄芪幼苗根系和地上部的生长并引起了植株MDA含量的显著升高以及新生叶片光合色素含量的降低,表明Cd处理对黄芪幼苗造成了较为明显的伤害。植株中吸收的Cd主要积累在黄芪幼苗根系,而运输到地上部的Cd积累规律为顶端<中部<基部,显示出黄芪幼苗可以通过对Cd的区域化降低其在地上部新生组织的积累。Cd处理降低了植株对多种矿质营养元素的吸收和转运,但是Ca和Mg却分别在地上部顶端和基部出现了明显的含量升高,推测其可能与降低Cd在新生组织的毒害作用以及提高老叶的Cd耐性有关。此外,根系中4种异黄酮物质的含量在Cd处理下明显升高,黄芪皂苷Ⅰ-Ⅳ的含量则被Cd处理所降低,暗示着异黄酮而非皂苷类物质在黄芪幼苗根系应对Cd胁迫中发挥了积极作用。

Physiological Mechanisms in Astragalus membranaceus Seedlings Responding to Cadmium Stress

The experiment was conducted to study the effects of different concentration Cd treatments on the growth, the adsorption and translocation of mineral elements, and the secondary metabolism of Astragalus membranaceus(Fisch.) Bunge(A. membranaceus), a traditional Chinese herb by employing a hydroponic system. The treatments of 25-200 μmol·L^-1 Cd significantly inhibited the biomass growth and induced the increasing of malondialdehyde(MDA) content in whole plant and the decreasing of photosynthetic pigment contents in the new leaves, obviously exhibiting adverse effects. The Cd adsorbed by the plant dominantly accumulated in the roots. The greatest proportion of the shoots Cd was accumulated in its underpart, and orderly followed by the middle and the upper parts. It suggested that the seedlings took the advantage of Cd compartmentalization to minimize the adverse impact on the growing tissues of the shoots. Cd exposure hindered the adsorptions and translocations of a variety of mineral nutrition elements. However, the contents of Ca and Mg markedly enhanced by the Cd treatments in the upper and under shoots, respectively. We presumed that this might play positive roles in reducing the harms of Cd in the growing and old leaves. Furthermore, the contents of four isoflavonoids were elevated by the Cd treatments in roots of the seedlings. On the contrary, the contents of astragaloside Ⅰ-Ⅳ were depressed. It was implied that the isoflavonoids rather than astragalosides helped the seedlings of A. membranaceus to counteract Cd stress in their roots.