Meristems

Abstract

A central feature of plant development is the continuous generation of organs throughout the lifespan of the plant. In the region designated the meristem, undifferentiated cells are maintained throughout the life cycle of the plant, providing a source of cells from which plant organs are derived. Cells that are differentiating as they are channelled toward a particular developmental fate also reside in the meristem, as do the resultant organ primordia. The meristem is a self‐renewing structure and its stem cell population is maintained at a near constant number despite the perpetual mobilisation of differentiating cells into organogenesis. The meristem's capacity to balance continuous differentiation of cells while replenishing the pool of undifferentiated, pluripotent cells is tightly controlled by a very complex and overlapping network of regulatory pathways. Key Concepts: Plants, unlike animals, have the capacity to generate new organs post‐embryonically, throughout the lifespan of the plant. Shoot and root apical meristems have the capacity to balance perpetual differentiation of cells while maintaining a population of undifferentiated stem cells. Because fates of meristematic cells are determined by their relative positions, they must be in continuous communication with their neighbouring cells. Signals can be transmitted from more mature cells to initial cells to specify the pattern of meristem differentiation. The number of stem cells in meristems is remarkably constant despite the continuous recruitment of differentiating cells into organs. In Arabidopsis shoot meristems, a feedback loop between WUSCHEL and the CLAVATA signalling pathway is crucial for specifying and maintaining the stem cell niche in the shoot apex. Within their niche boundaries, stem cells remain in an undifferentiated state in response to positional cues from neighbouring cells while cells displaced from the niche begin the process of differentiation.