Shaul Orit
Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel.
Biometals. 2002 Sep;15(3):309-23. doi: 10.1023/a:1016091118585.
The maintenance of Mg2+ homeostasis in the plant is essential for viability. This review describes Mg2+ functions and balancing in plants, with special focus on the existing knowledge of the involved transport mechanisms. Mg2+ is essential for the function of many cellular enzymes and for the aggregation of ribosomes. Mg2+ concentrations also modulate ionic currents across the chloroplast and the vacuolar membranes, and might thus regulate ion balance in the cell and stomatal opening. The significance of Mg2+ homeostasis has been particularly established with regard to Mg2+'s role in photosynthesis. Mg2+ is the central atom of the chlorophyll molecule, and fluctuations in its levels in the chloroplast regulate the activity of key photosynthetic enzymes. Relatively little is known of the proteins mediating Mg2+ uptake and transport in plants. The plant vacuole seem to play a key role in Mg2+ homeostasis in plant cells. Physiological and molecular evidence indicate that Mg2+ entry to the vacuole is mediated by Mg2+/H+ exchangers. The Arabidopsis vacuolar Mg2+/H+ exchanger, AtMHX, is highly transcribed at the vascular tissue, apparently most abundantly at the xylem parenchyma. Inclusion of Mg2+ ions into the vacuoles of this tissue may determine their partitioning between the various plant organs. Impacts of Mg2+ imbalance are described with respect for both plant physiology and for its nutritional value to animal and human.
植物体内镁离子稳态的维持对其生存至关重要。本综述描述了植物体内镁离子的功能及其平衡，特别关注了相关运输机制的现有知识。镁离子对许多细胞酶的功能以及核糖体的聚集至关重要。镁离子浓度还可调节叶绿体和液泡膜上的离子电流，从而可能调节细胞内的离子平衡和气孔开放。镁离子稳态的重要性在其光合作用中的作用方面尤为显著。镁离子是叶绿素分子的中心原子，叶绿体中其水平的波动会调节关键光合酶的活性。关于植物中介导镁离子吸收和运输的蛋白质，人们了解相对较少。植物液泡似乎在植物细胞镁离子稳态中起关键作用。生理和分子证据表明，镁离子进入液泡是由镁离子/氢离子交换体介导的。拟南芥液泡镁离子/氢离子交换体AtMHX在维管组织中高度转录，显然在木质部薄壁细胞中最为丰富。该组织液泡中镁离子的纳入可能决定其在植物各器官间的分配。文中描述了镁离子失衡对植物生理及其对动物和人类营养价值的影响。
