Cell size regulation in the meristem

Abstract

Among plants and animals, cell size is restricted at the tissue level. Especially in a tissue where cells are actively dividing, they maintain a uniform size by the coordination of cell division and cell growth. In the Arabidopsis inflorescence meristem, which can be observed for several days under confocal microscopy, cells often divide unevenly and cell size variation of daughter cells is greater than that of mother cells. This variation is, however, reduced in subsequent cell cycles by changing cell cycle length or relative growth rate (RGR), depending on cell size. Several studies combined observation with mathematical models and indicated that cell size-dependent cell cycle regulation could maintain cell size regardless of variation in daughter cell size or RGR. In addition, cells need to properly regulate their size in response to environmental stress. TOR (target of rapamycin) pathway or responses to phytohormones would be involved in this regulation because those are activated by environmental signals and affect cell cycle or cell growth. It is also suggested that altered meristem cell size may influence gene expression pattern or tissue-level molecule gradient. Therefore, cell size regulation in the meristem should have an important role in organogenesis.