Root Structure

How is the root organized longitudinally?

Moving from root tip toward the plant body (proximal), you will observe these structures: root cap, region of cell division, region of elongation, and the region of maturation

Region of Maturation (RoM)

  • Also, called the Region of Cell Differentiation

  • Proximal to RoE

  • Cells differentiate and mature

  • Root hairs created

  • Area of water absorption by plant

Region of Elongation (RoE)

  • An area proximal to the RCD and the apical meristem

  • Cells entering the G1 Period of Interphase

  • Cells expand in length

Region of Cell Division (RCD)

  • An area just behind the root cap

  • An area of active mitosis (cell division)

  • This is the Root Apical Meristem

Root Cap

  • The distal-most portion of the root

  • Cells created by the apical meristem to protect meristem

How is the root organized in cross-section?

Moving from the outside toward the center of the root, you will observe these structures: the epidermis, the cortex, the endodermis, the pericycle, and the vascular cylinder

Epidermis

  • The outer layer of cells that protects the root tissues

  • It is the "outer skin" (epi-dermis) of the organ

  • Root hairs are visible in the mature portions of the primary roots

Cortex

  • The area beneath the epidermis, up to the endodermis

  • This is mostly ground tissues that store materials and provide peripheral strength

Endodermis

  • A single ring-like band of cells that regulate water and mineral uptake

  • It is the "inner skin" (endo-dermis) of the organ

  • The cells have special thickening called Casparian Strips

    • Lignin (not suberin) coats the cells on the radial and transverse walls, which prevents passive movement of water from the cortex to the vascular cylinder (Geldner 2013)

    • Therefore, the plant has to actively move water into the vascular cylinder (symplastic transport)

Pericycle

  • Underneath the endodermis, is a single ring-like band of cells that creates lateral roots

  • These pericycle cells are embryonic, and not thickened

Vascular Cylinder or Stele

  • The vascular cylinder, or stele, are the names given to the area that includes the xylem and phloem

  • In young roots, the stele is composed of primary xylem and primary phloem, which formed from the root apical meristem