植物对硅的吸收转运机制研究进展

硅(Si)能缓解生物与非生物胁迫对植物的毒害作用,Si的吸收转运是由Si转运蛋白介导的.最近,多个Si转运蛋白(Lsi)基因相继在水稻、大麦和玉米中被克隆出来,并在Si的吸收转运机制方面取得了很大进展.水稻OsLsi在根组织中呈极性分布,OsLsi1定位在根外皮层和内皮层凯氏带细胞外侧质膜,负责将外部溶液中的单硅酸转运到皮层细胞内.OsLsi2定位在凯氏带细胞内侧质膜,在外皮层中负责将Si输出到通气组织质外体中,在内皮层与OsLsi1协同作用将Si转运到中柱中.导管中的Si通过蒸腾流转运到地上部,再由定位在叶鞘和叶片木质部薄壁细胞靠近导管一侧的OsLsi6负责木质部Si的卸载和分配.在大麦和玉米中,ZmLsi1/HvLsi1定位在根表皮和皮层细胞外侧质膜负责Si的吸收,然后Si通过共质体途径被转运到内皮层凯氏带细胞中,再由ZmLsi2/HvLsi2输出转运到中柱中.ZmLsi6在细胞中的定位和活性与OsLsi6相似,推测其可能具有类似的功能,但大麦Lsi6至今未见报道.所以,Si转运机制仍需要进一步研究.

Advances in The Uptake and Translocation of Silicon in Plants

Silicon exerts beneficial effects on plant growth and development by alleviating biotic and abiotic stresses. The uptake and translocation of Si in plants is mediated by Si transporters, recently, several genes encoding Si transporters have been identified from rice, barley and maize. OsLsi shows polar localization in root tissues, OsLsi1 is localized at the plasma membrane of both exodermis and endodermis on the distal side in rice roots, where Casparian strips exist; OsLsi2 is localized on the proximal side of the same cells. Therefore, OsLsi1 is responsible for transport of Si from the external solution to the root cells, whereas OsLsi2 is an efflux transporter responsible for the transport of Si from the exodermal cells to the apoplast of aerenchyma; Si is transported into the stele by OsLsi1 and OsLsi2 coordination and then translocated to the shoot by transpirational flow through the xylem. OsLsi6 was observed in the xylem parenchyma cells that were adjacent to vessels in both leaf sheaths and leaf blades besides roots, which is responsible for the export of Si from the xylem and for the subsequent distribution of Si. In maize and barley, Si is taken up from the external solution by the influx transporter (ZmLsi1/HvLsi1) localized on the distal side of cells in the epidermis and cortex layer, and then transferred to the endodermis through the symplastic pathway. At the endodermis, Si is released by an active Si efflux transporter (ZmLsi2/HvLsi2) to the stele. In addition, ZmLsi6 has the similar the localization and transport activity with OsLsi6 and might have similar functions, however, the Lsi6 in barley is not identified until now. More researches in the mechanism of Si transport in plant are needed further.