Brigham L. A., Woo H. H., Nicoll S. M., Hawes M. C.
Departments of Plant Pathology and Molecular and Cellular Biology, University of Arizona, Tucson, Arizona 85721.
Plant Physiol. 1995 Oct;109(2):457-463. doi: 10.1104/pp.109.2.457.
Many plants release large numbers of metabolically active root border cells into the rhizosphere. We have proposed that border cells, cells produced by the root cap meristem that separate from the rest of the root upon reaching the periphery of the cap, are a singularly differentiated part of the root system that modulates the environment of the plant root by producing specific substances to be released into the rhizosphere. Proteins synthesized in border cells exhibit profiles that are very distinct from those of the root tip (root cap, root meristem, and adjacent cells). In vivo-labeling experiments demonstrate that 13% of the proteins that are abundant in preparations from border cells are undetectable in root tip preparations. Twenty-five percent of the proteins synthesized by border cells in a 1-h period are rapidly excreted into the incubation medium. Quantitative variation in levels of specific marker proteins, including glutamine synthetase, heat-shock protein 70, and isoflavone reductase, also occurs between border cells and cells in the root tip. mRNA differential-display assays demonstrate that these large qualitative and quantitative differences in protein expression are correlated with similarly distinct patterns of gene expression. These observations are consistent with the hypothesis that a major switch in gene expression accompanies differentiation into root border cells, as expected for cells with specialized functions in plant development.
许多植物会向根际释放大量具有代谢活性的根边缘细胞。我们提出，边缘细胞是由根冠分生组织产生的细胞，当到达根冠外围时与根的其余部分分离，它们是根系中一个独特分化的部分，通过产生特定物质释放到根际来调节植物根的环境。在边缘细胞中合成的蛋白质表现出与根尖（根冠、根分生组织和相邻细胞）非常不同的特征。体内标记实验表明，在边缘细胞提取物中大量存在的蛋白质，有13%在根尖提取物中检测不到。边缘细胞在1小时内合成的蛋白质中有25%会迅速分泌到培养液中。包括谷氨酰胺合成酶、热休克蛋白70和异黄酮还原酶在内的特定标记蛋白水平在边缘细胞和根尖细胞之间也存在定量差异。mRNA差异显示分析表明，这些蛋白质表达上的巨大质和量的差异与同样不同的基因表达模式相关。这些观察结果与以下假设一致，即基因表达的重大转变伴随着向根边缘细胞的分化，这正如在植物发育中具有特定功能的细胞所预期的那样。
