Laufs P, Grandjean O, Jonak C, Kiêu K, Traas J
Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique, Route de Saint Cyr, 78026 Versailles Cedex, France.
Plant Cell. 1998 Aug;10(8):1375-90. doi: 10.1105/tpc.10.8.1375.
The shoot apical meristem (SAM) is a small group of dividing cells that generate all of the aerial parts of the plant. With the goal of providing a framework for the analysis of Arabidopsis meristems at the cellular level, we performed a detailed morphometric study of actively growing inflorescence apices of the Landsberg erecta and Wassilewskija ecotypes. For this purpose, cell size, spatial distribution of mitotic cells, and the mitotic index were determined in a series of optical sections made with a confocal laser scanning microscope. The results allowed us to identify zones within the inflorescence SAM with different cell proliferation rates. In particular, we were able to define a central area that was four to six cells wide and had a low mitotic index. We used this technique to compare the meristem of the wild type with the enlarged meristems of two mutants, clavata3-1 (clv3-1) and mgoun2 (mgo2). One of the proposed functions of the CLV genes is to limit cell division rates in the center of the meristem. Our data allowed us to reject this hypothesis, because the mitotic index was reduced in the inflorescence meristem of the clv3-1 mutant. We also observed a large zone of slowly dividing cells in meristems of clv3-1 seedlings. This zone was not detectable in the wild type. These results suggest that the central area is increased in size in the mutant meristem, which is in line with the hypothesis that the CLV3 gene is necessary for the transition of cells from the central to the peripheral zone. Genetic and microscopic analyses suggest that mgo2 is impaired in the production of primordia, and we previously proposed that the increased size of the mgo2 meristem could be due to an accumulation of cells at the periphery. Our morphometric analysis showed that mgo2 meristems, in contrast to those of clv3-1, have an enlarged periphery with high cell proliferation rates. This confirms that clv3-1 and mgo2 lead to meristem overgrowth by affecting different aspects of meristem function.
茎尖分生组织（SAM）是一小群进行分裂的细胞，可产生植物的所有地上部分。为了提供一个在细胞水平上分析拟南芥分生组织的框架，我们对Landsberg erecta和Wassilewskija生态型的活跃生长的花序顶端进行了详细的形态计量学研究。为此，在共聚焦激光扫描显微镜制作的一系列光学切片中测定了细胞大小、有丝分裂细胞的空间分布和有丝分裂指数。这些结果使我们能够识别花序SAM内具有不同细胞增殖率的区域。特别是，我们能够定义一个宽四到六个细胞且有丝分裂指数较低的中心区域。我们使用这项技术将野生型的分生组织与两个突变体clavata3-1（clv3-1）和mgoun2（mgo2）的扩大分生组织进行比较。CLV基因的一个推测功能是限制分生组织中心的细胞分裂速率。我们的数据使我们能够否定这一假设，因为在clv3-1突变体的花序分生组织中有丝分裂指数降低。我们还在clv3-1幼苗的分生组织中观察到一个大的缓慢分裂细胞区域。在野生型中未检测到该区域。这些结果表明，突变体分生组织的中心区域大小增加，这与CLV3基因对于细胞从中心区域向周边区域转变是必需的这一假设一致。遗传和显微镜分析表明，mgo2在原基产生方面存在缺陷，并且我们之前提出mgo2分生组织增大的原因可能是周边细胞的积累。我们的形态计量分析表明，与clv3-1不同，mgo2分生组织的周边扩大且细胞增殖率高。这证实了clv3-1和mgo2通过影响分生组织功能的不同方面导致分生组织过度生长。
