Lateral Root - Early Morphological Changes

Early Morphological Changes

The following description is for early events in lateral root formation of the model organism Arabidopsis thaliana, where lateral roots typically form when the plant is between seven and nine days old.

• Stage I: The first morphologically identifiable stage is the asymmetric division of two cells of the pericycle, termed pericycle founder cells, which are adjacent to the protoxylem poles and from which the lateral roots are derived entirely. These cells then undergo further division, causing radial expansion.
• Stage II: The small, central cells then divide periclinally (parallel to the surface of the plant body) in a series of transverse, asymmetric divisions such that the young primordium becomes visible as a projection made up of an inner layer and an outer layer.
• Stages III and IV: At the third stage, the outer layer of cells divide so that the primordium is now made of three layers. The fourth stage is then characterised by the inner layer undergoing a similar division, such that four cell layers are visible.
• Stages V to VIII: Expansion and further division of these four layers eventually results in the emergence of the young lateral root from the parent tissue (the overlying tissue of the primary root) at stage eight.