提出问题：In plants, positional information provided by the hormone auxin regulates rhythmic organ production at the shoot apex, but the spatio-temporal dynamics of auxin gradients is unknown.

研究方法：We used quantitative imaging to demonstrate that auxin carries high-definition graded information not only in space but also in time.

研究结果：We show that, during organogenesis, temporal patterns of auxin arise from rhythmic centrifugal waves of high auxin travelling through the tissue faster than growth. We further demonstrate that temporal integration of auxin concentration is required to trigger the auxin-dependent transcription associated with organogenesis.

结论：This provides a mechanism to temporally differentiate sites of organ initiation and exemplifies how spatio-temporal positional information can be used to create rhythmicity.

Plants, like animals and many other multicellular organisms, control their body architecture by creating organized patterns of cells. These patterns are generally defined by signal molecules whose levels differ across the tissue and change over time. This tells the cells where they are located in the tissue and therefore helps them know what tasks to perform.

与动物和其它多细胞生物一样，植物通过有组织化的细胞模式来控制其植株结构。这些模式通常是由随着时间不断变化、并且在不同组织中的水平存在差异的信号分子所决定的。这些信号分子的时空波动告诉细胞其在组织中所处的空间位置，从而精确告诉每一个细胞具体该执行何种功能与任务。

A plant hormone called auxin is one such signal molecule and it controls when and where plants produce new leaves and flowers. Over time, this process gives rise to the dashing arrangements of spiraling organs exhibited by many plant species. The leaves and flowers form from a relatively small group of cells at the tip of a growing stem known as the shoot apical meristem.

有一个植物激素叫做生长素，其作为信号分子的一种，可以控制何时、何地产生新的叶片和花。长此以往，这种依赖于生长素的进程导致了许多植物中所表现出的螺旋器官排列。植物的叶片和花都来源于正在生长的茎的尖端一小群细胞，这一小群细胞叫做茎尖分生组织。

Auxin accumulates at precise locations within the shoot apical meristem before cells activate the genes required to make a new leaf or flower. However, the precise role of auxin in forming these new organs remained unclear because the tools to observe the process in enough detail were lacking.

在细胞中激活新叶或花形成必需相关基因之前，生长素就在茎尖分生组织特定的位置上开始积累。然而，由于缺乏高清分辨率的工具，生长素如何确切地作用于花叶等新器官的形成还存在很多未知的方面。

Galvan-Ampudia, Cerutti et al. have now developed new microscopy and computational approaches to observe auxin in a small plant known as Arabidopsis thaliana. This showed that dozens of shoot apical meristems exhibited very similar patterns of auxin. Images taken over a period of several hours showed that the locations where auxin accumulated were not fixed on a group of cells but instead shifted away from the center of the shoot apical meristems faster than the tissue grew. This suggested the cells experience rapidly changing levels of auxin. Further experiments revealed that the cells needed to be exposed to a high level of auxin over time to activate genes required to form an organ. This mechanism sheds a new light on how auxin regulates when and where plants make new leaves and flowers. The tools developed by Galvan-Ampudia, Cerutti et al. could be used to study the role of auxin in other plant tissues, and to investigate how plants regulate the response to other plant hormones. 

Galvan-Ampudia等人开发了一个新的显微观测和计算方法，用以观测拟南芥中生长素的分布动态。该研究显示，数十个茎尖分生组织都存在类似的生长素模式。持续数小时的图像监测，作者发现积累生长素的位置在一群细胞中并不是固定的，相反其从茎尖分生组织中心往外迁移的速率远快于组织生长的速度。这说明细胞经历了快速的生长素含量变化。进一步的实验揭示了细胞需要暴露在一个高水平的生长素浓度下一段时间，以此激活对于器官形成至关重要的基因的表达。本文的研究为生长素如何植物何时、何地生成新的叶片和花组织提供了新的视野。由Galvan-Ampudia等人所开发这套工具同样适用于其它植物组织中的生长素功能研究，以及探索植物是如何响应于其它植物激素的。