Kim Sung-Yong, Sivaguru Mayandi, Stacey Gary
National Center for Soybean Biotechnology and Division of Plant Sciences , University of Missouri, Columbia, Missouri 65211, USA.
Plant Physiol. 2006 Nov;142(3):984-92. doi: 10.1104/pp.106.085670. Epub 2006 Sep 8.
Extracellular ATP (eATP) in animals is well documented and known to play an important role in cellular signaling (e.g. at the nerve synapse). The existence of eATP has been postulated in plants; however, there is no definitive experimental evidence for its presence or an explanation as to how such a polar molecule could exit the plant cell and what physiological role it may play in plant growth and development. The presence of eATP in plants (Medicago truncatula) was detected by constructing a novel reporter; i.e. fusing a cellulose-binding domain peptide to the ATP-requiring enzyme luciferase. Application of this reporter to plant roots allowed visualization of eATP in the presence of the substrate luciferin. Luciferase activity could be detected in the interstitial spaces between plant epidermal cells and predominantly at the regions of actively growing cells. The levels of eATP were closely correlated with regions of active growth and cell expansion. Pharmacological compounds known to alter cytoplasmic calcium levels revealed that ATP release is a calcium-dependent process and may occur through vesicular fusion, an important step in the polar growth of actively growing root hairs. Reactive oxygen species (ROS) activity at the root hair tip is not only essential for root hair growth, but also dependent on the cytoplasmic calcium levels. Whereas application of exogenous ATP and a chitin mixture increased ROS activity in root hairs, no changes were observed in response to adenosine, AMP, ADP, and nonhydrolyzable ATP (betagammameATP). However, application of exogenous potato (Solanum tuberosum) apyrase (ATPase) decreased ROS activity, suggesting that cytoplasmic calcium gradients and ROS activity are closely associated with eATP release.
动物细胞外ATP(eATP)已有充分的文献记载,并且已知其在细胞信号传导中发挥重要作用(例如在神经突触处)。植物中已推测存在eATP;然而,对于其存在与否并没有确凿的实验证据,也没有关于这样一个极性分子如何能够离开植物细胞以及它在植物生长发育中可能发挥何种生理作用的解释。通过构建一种新型报告基因检测了植物(蒺藜苜蓿)中eATP的存在;即,将纤维素结合结构域肽与需要ATP的荧光素酶融合。将该报告基因应用于植物根部,可以在底物荧光素存在的情况下观察到eATP。在植物表皮细胞之间的间隙中,主要是在活跃生长细胞的区域可以检测到荧光素酶活性。eATP的水平与活跃生长和细胞扩张的区域密切相关。已知能改变细胞质钙水平的药理化合物表明,ATP释放是一个钙依赖性过程,可能通过囊泡融合发生,这是活跃生长的根毛极性生长中的一个重要步骤。根毛尖端的活性氧(ROS)活性不仅对根毛生长至关重要,而且还依赖于细胞质钙水平。虽然施加外源ATP和几丁质混合物会增加根毛中的ROS活性,但对腺苷、AMP、ADP和不可水解的ATP(βγ-甲基ATP)没有观察到变化。然而,施加外源马铃薯(茄属)焦磷酸酶(ATPase)会降低ROS活性,这表明细胞质钙梯度和ROS活性与eATP释放密切相关。