Reddy G Venugopala, Heisler Marcus G, Ehrhardt David W, Meyerowitz Elliot M
California Institute of Technology, Division of Biology, MC 156-29, 1200 E. California Boulevard, Pasadena, CA 91125, USA.
Development. 2004 Sep;131(17):4225-37. doi: 10.1242/dev.01261. Epub 2004 Jul 27.
Precise knowledge of spatial and temporal patterns of cell division, including number and orientation of divisions, and knowledge of cell expansion, is central to understanding morphogenesis. Our current knowledge of cell division patterns during plant and animal morphogenesis is largely deduced from analysis of clonal shapes and sizes. But such an analysis can reveal only the number, not the orientation or exact rate, of cell divisions. In this study, we have analyzed growth in real time by monitoring individual cell divisions in the shoot apical meristems (SAMs) of Arabidopsis thaliana. The live imaging technique has led to the development of a spatial and temporal map of cell division patterns. We have integrated cell behavior over time to visualize growth. Our analysis reveals temporal variation in mitotic activity and the cell division is coordinated across clonally distinct layers of cells. Temporal variation in mitotic activity is not correlated to the estimated plastochron length and diurnal rhythms. Cell division rates vary across the SAM surface. Cells in the peripheral zone (PZ) divide at a faster rate than in the central zone (CZ). Cell division rates in the CZ are relatively heterogeneous when compared with PZ cells. We have analyzed the cell behavior associated with flower primordium development starting from a stage at which the future flower comprises four cells in the L1 epidermal layer. Primordium development is a sequential process linked to distinct cellular behavior. Oriented cell divisions, in primordial progenitors and in cells located proximal to them, are associated with initial primordial outgrowth. The oriented cell divisions are followed by a rapid burst of cell expansion and cell division, which transforms a flower primordium into a three-dimensional flower bud. Distinct lack of cell expansion is seen in a narrow band of cells, which forms the boundary region between developing flower bud and the SAM. We discuss these results in the context of SAM morphogenesis.
精确了解细胞分裂的时空模式，包括分裂的数量和方向，以及细胞扩张情况，对于理解形态发生至关重要。我们目前对动植物形态发生过程中细胞分裂模式的了解，很大程度上是通过对克隆形状和大小的分析推断出来的。但这种分析只能揭示细胞分裂的数量，而无法揭示其方向或确切速率。在本研究中，我们通过监测拟南芥茎尖分生组织（SAMs）中的单个细胞分裂来实时分析生长情况。实时成像技术促成了细胞分裂模式时空图的绘制。我们整合了细胞随时间的行为以可视化生长过程。我们的分析揭示了有丝分裂活性的时间变化，并且细胞分裂在克隆上不同的细胞层之间是协调的。有丝分裂活性的时间变化与估计的叶龄期长度和昼夜节律无关。细胞分裂速率在SAM表面各不相同。外周区（PZ）的细胞比中央区（CZ）的细胞分裂速度更快。与PZ细胞相比，CZ中的细胞分裂速率相对不均匀。我们从未来花在L1表皮层包含四个细胞的阶段开始，分析了与花原基发育相关的细胞行为。原基发育是一个与独特细胞行为相关的连续过程。原基祖细胞及其近端细胞中的定向细胞分裂与原基的初始生长有关。定向细胞分裂之后是细胞扩张和细胞分裂的快速爆发，这将花原基转变为三维花芽。在形成发育中的花芽与SAM之间边界区域的窄带细胞中，明显缺乏细胞扩张。我们在SAM形态发生的背景下讨论了这些结果。
