Topic 8: Plant Growth - Roots

Taproot

In most eudicots, this is the first root to grow and serves as the main vertical root

Lateral Roots

Secondary branches that arise from the taproot. They originate from meristematically active regions within the pericycle

Fibrous Roots

• A shallow network of roots characteristic of most monocots, where the primary root dies and is replaced by many new roots coming off the stem, with no single branch predominating

Epiphyte

A plant that grows on the surface of another plant

Root Cap

A terminal structure that protects the root apical meristem (RAM) as it grows through the soil. It secretes a slime called mucilage to ease passage and is the primary site of gravity perception

Zone of Cell Division

The area at the root tip that includes the RAM and its immediate undifferentiated products where new cells are created

Zone of Cell Elongation

The region where cells can grow up to ten times their initial length, providing the force that pushes the root tip further into the soil

Zone of Cell Differentiation

The area where cells mature and take on distinct identities; for example, this is where root hairs emerge

Cortex

A region of ground tissue consisting of starch-storing parenchyma cells with intercellular spaces

Endodermis

The innermost layer of the cortex, only one cell thick, which forms a selective boundary between the ground tissue and the vascular cylinder

Pericycle

The outermost layer of the vascular cylinder, located just inside the endodermis, surrounding the xylem and phloem

Macronutrient

• Essential elements required by plants in large amounts (1–4% of dry weight), such as Nitrogen, Phosphorus, and Potassium

• C, H, O -> fixed as sugars by photosynthesis (H2O+CO2)

Micronutrient

• Essential elements required in very small amounts, primarily serving as enzymatic co-factors

• too much can be bad

Apoplast (Apoplastic Route)

• A transport pathway consisting of everything exterior to the plasma membranes, including cell walls and intercellular spaces

• this route eventualluy gets blocked by the casparian strip

Symplast (Symplastic Route)

A transport pathway consisting of the entire mass of cytosol of all living plant cells, which are connected by plasmodesmata

Transmembrane Route

A route where substances move out of one cell, across the cell wall, and into the neighboring cell, requiring them to cross plasma membranes

Plasmodesmata

Channels passing through cell walls that connect the cytoplasm of adjacent cells, allowing for symplastic transport

Casparian Strip

A belt of waxy lignin located in the transverse and radial walls of endodermal cells. It blocks the apoplastic route, forcing water and minerals to cross a plasma membrane to enter the vascular cylinder