Cell enlargement, maturation, and differentiation

Abstract

The root and shoot apical meristems are the source of all the cells for the continued extension of the plant body. Meristems grow away from the more basal cells that they have produced but, when measuring their growth, it is more convenient to use the meristem as the point of reference rather than some arbitrary point in the basal non-growing regions. We can then regard the cells as being displaced away from the growing tip by the growth of the cells of the apical meristem more distal to them. As they are displaced, the cells differentiate into the tissue systems of epidermis, cortex, and stele (and root cap in the root), and into the different cell types-xylem, phloem, fibres, pith, etc. As cells pass out of the meristem they stop dividing, they enlarge and vacuolate, and then stop growing. This cell growth is common to all cell and tissue types. It is accompanied by a loss of meristematic activity and ends with cessation of growth, and has been called cell maturation. This emphasizes that, although it may be regarded as a generalized differentiation of cells behind the meristem, it is a process that is superimposed on the differentiation of cell and tissues types.