Sherson Sarah M, Alford Heather L, Forbes Susan M, Wallace Graham, Smith Steven M
Institute of Cell and Molecular Biology, University of Edinburgh, The King's Buildings, Mayfield Road, Edinburgh EH9 3JH, Scotland, UK.
J Exp Bot. 2003 Jan;54(382):525-31. doi: 10.1093/jxb/erg055.
The hydrolysis of sucrose by cell-wall invertases (cwINV) and the subsequent import of hexoses into target cells appears to be crucial for appropriate metabolism, growth and differentiation in plants. Hexose uptake from the apoplast is catalysed by monosaccharide/H+ symporters (Sugar Transport Proteins or STPs), which have the potential to sense sugars. Import of extracellular hexoses may generate signals to orchestrate cellular activities, or simply feed metabolic pathways distinct from those fed by sucrose. It is predicted that Arabidopsis has six cwINV genes and at least 14 STP genes. These genes show different spatial and temporal patterns of expression, and several knock-out mutants have been isolated for analysis. AtSTP1 transports glucose, galactose, xylose, and mannose, but not fructose. It accounts for the majority of the AtSTP activity in vegetative tissues and its activity is markedly repressed by treatment with exogenous sugars. These observations are consistent with a role in the retrieval of cell-wall-derived sugars, for example, during carbohydrate limitation or cell expansion. The AtSTP1 gene is also expressed in developing seeds, where it might be responsible for the uptake of glucose derived from imported sucrose. The large number of AtcwINV and AtSTP genes, together with complex patterns of expression for each, and the possibility that each protein may have more than one physiological function, provides the plant with the potential for a multiplicity of patterns of monosaccharide utilization to direct growth and differentiation or to respond flexibly to changing environmental conditions.
细胞壁转化酶（cwINV）催化蔗糖水解，随后己糖被转运至靶细胞，这一过程对于植物的正常代谢、生长和分化似乎至关重要。质外体中己糖的摄取由单糖/H⁺共转运体（糖转运蛋白或STP）催化，这些共转运体具有感知糖类的潜力。细胞外己糖的转运可能会产生信号来协调细胞活动，或者仅仅为不同于蔗糖供能的代谢途径提供能量。据预测，拟南芥有6个cwINV基因和至少14个STP基因。这些基因表现出不同的时空表达模式，并且已经分离出了几个基因敲除突变体用于分析。AtSTP1转运葡萄糖、半乳糖、木糖和甘露糖，但不转运果糖。它在营养组织的AtSTP活性中占大部分，并且其活性会被外源糖处理显著抑制。这些观察结果与AtSTP1在回收细胞壁衍生糖类中的作用一致，例如在碳水化合物限制或细胞扩张期间。AtSTP1基因也在发育中的种子中表达，在那里它可能负责摄取源自输入蔗糖的葡萄糖。大量的AtcwINV和AtSTP基因，以及每个基因复杂的表达模式，还有每个蛋白质可能具有不止一种生理功能的可能性，为植物提供了多种单糖利用模式的潜力，以指导生长和分化或灵活应对不断变化的环境条件。
