Department of Biology, University of Essex, Colchester CO4 3SQ, United Kingdom.
Plant Physiol. 2011 Jul;156(3):1375-85. doi: 10.1104/pp.111.174722. Epub 2011 May 11.
Extracellular purine nucleotides are implicated in the control of plant development and stress responses. While extracellular ATP is known to activate transcriptional pathways via plasma membrane (PM) NADPH oxidase and calcium channel activation, very little is known about signal transduction by extracellular ADP. Here, extracellular ADP was found to activate net Ca(2+) influx in roots of Arabidopsis (Arabidopsis thaliana) and transiently elevate cytosolic free Ca(2+) in root epidermal protoplasts. An inward Ca(2+)-permeable conductance in root epidermal PM was activated within 1 s of ADP application and repeated application evoked a smaller current. Such response speed and densitization are consistent with operation of equivalents to animal ionotropic purine receptors, although to date no equivalent genes for such receptors have been identified in higher plants. In contrast to ATP, extracellular ADP did not evoke accumulation of intracellular reactive oxygen species. While high concentrations of ATP caused net Ca(2+) efflux from roots, equivalent concentrations of ADP caused net influx. Overall the results point to a discrete ADP signaling pathway, reliant on receptor-like activity at the PM.
细胞外嘌呤核苷酸参与植物发育和应激反应的调控。虽然已知细胞外 ATP 通过质膜 (PM) NADPH 氧化酶和钙通道激活来激活转录途径，但对于细胞外 ADP 的信号转导知之甚少。在这里，发现细胞外 ADP 激活了拟南芥（Arabidopsis thaliana）根部的净 Ca（2+）内流，并瞬时增加了根表皮原生质体中的细胞质游离 Ca（2+）。ADP 应用后 1 秒内激活了根表皮 PM 中的内向 Ca（2+）渗透性电导，重复应用会引起较小的电流。这种响应速度和密度与动物离子型嘌呤受体的作用一致，尽管迄今为止在高等植物中尚未鉴定出此类受体的等效基因。与 ATP 不同，细胞外 ADP 不会引发细胞内活性氧物质的积累。虽然高浓度的 ATP 导致根中净 Ca（2+）流出，但等效浓度的 ADP 导致净流入。总的来说，结果表明存在离散的 ADP 信号通路，该通路依赖于质膜上的受体样活性。
