Phases of Growth in Plants

Growth is a complex, multi-phase process. Meristematic cells undergo four distinct phases: cell division, elongation, maturation, and differentiation.

 

Cell Division Phase

In this phase, meristematic cells undergo mitotic division to generate new cells. This stage primarily occurs at the tips of roots and shoots, characterized by (i) small cell size, (ii) spherical nuclei positioned toward the cytoplasm's center, (iii) absence of vacuoles in the cytoplasm, and (iv) post-division enlargement of daughter cells through the synthesis of cytoplasm and cell wall materials.

The Root tip (LS) is divided into four sizes

Elongation Phase

The zone of cell elongation follows the cell division region in both roots and shoots. During this phase, (i) cytoplasm synthesis increases the cell's dry weight, (ii) the formation of vacuoles leads to increased cell wall plasticity, resulting in irreversible cell wall elongation, and (iii) a significant uptake of water occurs via osmosis.

 

Maturation Phase

At this stage, cells reach their final size. Cells destined to become pith or cortex do not elongate significantly along the longitudinal axis. In contrast, fibers and tracheids exhibit substantial elongation parallel to the stem or root's long axis and limited elongation in other directions.

 

Differentiation Phase

During this phase, cell wall differentiation initiates, and cell walls thicken as cell elongation ceases. The thickening is usually uneven, with various cell types and tissue elements, such as tracheids and xylem, developing pitted cell walls. Cells across different tissues vary in spatial dimensions, and numerous new structural features emerge during this phase.