9.3 - Growth in Plants

Types of plant tissues

Dermal tissue: outer covering that protects

Ground tissue: thin-celled walls that have functions related to storage, photosynthesis, support, secretion

Vascular tissue: xylem and phloem, used for transport and support

• All arise from meristematic tissue: small clusters of undifferentiated cells that can specialize into types of plant tissues

Plant tissues and meristems

Apical meristem

• Occurs at tips of roots and stems

• Responsible for primary growth up and down (growing taller, extending roots)

• Results in soft tissue (non-woody stems, roots)

Lateral meristem

• Occurs at roots and stems

• Responsible for secondary growth (growing in diamter)

• Vascular cambium: produces more vascular bundles, which is a major component of wood

• Cork cambium: occurs within bark and produces cork cells

Factors influencing plant growth - hormones

Functions of membrane proteins: junction, enzymes, transport, recognition, anchorage, transduction (hormone binding)

• Many cells produce the same hormone that has many different effects depending on location of the receptor cell

1. Protein receptors in or on a specific plant cell receives stimulus from the environment, such as light

2. The protein receptor becomes activated

3. Activated protein receptor initiates a metabolic pathwya

4. Metabolic pathway produces a hormone

5. The hormone travels through the phloem

Plant hormone

Tropism: growth or movement in response to environmental stimuli (chemicals, gravity)

Phototropism: plant growth in response to light

• Necessary because it allows plants to compete for light or to maximize their exposure to light

1. Auxin is a plant hormone that is equally distributed in the plant cells

2. To bend towards light, auxin is actively pumped OUT of the cell that are closest to the light

3. Auxin accumulates in the space between cells

4. Auxin diffuses into the cells that are farthest from the light (passive)

5. Increased auxin levels activates genes that code from a specific enzyme

6. The enzyme causes the cell walls of the cells farthest from light to elongate

7. Elongation of cells away from the light cause the plant to bend toward the light

• Auxin also helps…

  • Stimulation of mitosis in meristematic tissue

  • Differentiation of xylem and phloem

    • Development of roots

Micropropagation

Using cells from the shoot apex (apical meristem, non-differentiated cells) to produce more individual plants

• A way to help preserve populations of endangered plants