Barkla B J, Apse M P, Manolson M F, Blumwald E
Department of Botany, University of Toronto, ON, Canada.
Symp Soc Exp Biol. 1994;48:141-53.
Salt stress imposes severe limitations on plant growth, however, the extent of growth reduction depends upon the soil salinity level and the plant species. One of the mechanisms employed by salt tolerant plants is the effective vacuolar compartmentalization of sodium. The sequestration of sodium into the vacuole occurs by the operation of a Na+/H+ antiport located at the tonoplast. Evidence for a plant vacuolar Na+/H+ antiport has been demonstrated in tissues, intact vacuoles and isolated tonoplast vesicles. In sugar beet cell suspensions, the activity of the vacuolar Na+/H+ antiport increased with increasing NaCl concentrations in the growth medium. This increased activity was correlated with the increased synthesis of a 170 kDa tonoplast polypeptide. In vivo labelling of tonoplast proteins showed the enhanced synthesis of the 170 kDa polypeptide not only upon exposure of the cells to salt, but also when the cells were grown in the presence of amiloride. Exposure of the cells to amiloride also resulted in increased vacuolar Na+/H+ antiport activity. Polyclonal antibodies raised against the 170 kDa polypeptide almost completely inhibited the antiport activity, suggesting the association of this protein with the plant vacuolar Na+/H+ antiport. Antibodies against the Na+/H+ antiport-associated polypeptide were used to screen a Beta lambda ZAP expression library. A partial clone of 1.65 kb was sequenced and found to encode a polypeptide with a putative transmembrane domain and a large hydrophilic C terminus. This clone showed no homology to any previously cloned gene at either the nucleic acid or the amino acid level.
盐胁迫对植物生长造成严重限制，然而，生长减少的程度取决于土壤盐度水平和植物种类。耐盐植物采用的机制之一是将钠有效地分隔在液泡中。钠通过位于液泡膜上的Na+/H+反向转运蛋白进入液泡。在组织、完整液泡和分离的液泡膜囊泡中已证明存在植物液泡Na+/H+反向转运蛋白的证据。在甜菜细胞悬浮液中，液泡Na+/H+反向转运蛋白的活性随着生长培养基中NaCl浓度的增加而增加。这种活性增加与一种170 kDa液泡膜多肽的合成增加相关。液泡膜蛋白的体内标记显示，不仅细胞暴露于盐时，而且细胞在氨氯吡脒存在下生长时，170 kDa多肽的合成都会增强。细胞暴露于氨氯吡脒也导致液泡Na+/H+反向转运蛋白活性增加。针对170 kDa多肽产生的多克隆抗体几乎完全抑制了反向转运蛋白活性，表明该蛋白与植物液泡Na+/H+反向转运蛋白有关。针对与Na+/H+反向转运蛋白相关的多肽的抗体用于筛选β噬菌体λZAP表达文库。对一个1.65 kb的部分克隆进行测序，发现其编码一个具有推定跨膜结构域和一个大的亲水性C末端的多肽。该克隆在核酸或氨基酸水平上与任何先前克隆的基因均无同源性。
