MGSLG. (2020). Module 3 Unit 1 study guide

The general functions of auxins, gibberellins and abscisic acid

Terminology & definitions

Biological term

Description

Abscisic acid

The plant hormone that promotes seed dormancy

A plant hormone that causes leaves to fall off trees in autumn.

Apical dominance

Is the phenomenon whereby the main, central stem of the plant is dominant over other side stems

Auxins

The plant hormone that promotes root and stem growth

Geotropism

The growth of part of a plant in response to gravity.

Gibberellins

A plant growth hormone that stimulates seed germination.

Herbicide

Chemical used to kill weeds

Hormone

Chemicals that allow a plant to respond to some stimulus in the environment

Phototropism

The growth of a plant in response to light

Tropism

The growth movement of a plant or part of a plant in response to an environmental stimulus

Uniform light

A plant receives light of the same quality from all directions

Unilateral light

A plant received light from one direction only

Growth development in plants

  • Plants respond to stimuli in the environment by growing towards or away from the stimulus
  • This growth movement is controlled by plant hormones such as auxins, gibberellins, and abscisic acid
  • These substances are not true hormones because they work in the part of the plant where they are produced
  • Therefore, they are also referred to as plant growth substances
  • These allow plants to respond to certain stimuli in the environment:
    • Allow plants to bloom at an appropriate time
    • Allow plants to grow toward a light source
    • Allow seeds to germinate at the appropriate time
    • Induce dormancy in plants at the appropriate time

Fuseschool - Global Education. (2017). Plant hormaones: Tropisms (standard YouTube licence)

The role of auxins

Auxins stimulate the following responses in plants:

  • Cell division
  • Cell elongation (growth in stem length)
  • The development of fruit
  • The abscission of leaves and fruit
  • The development of adventitious root in stem cuttings
  • Tropic movement in stem and roots
  • Apical dominance: it suppresses the growth of the lateral buds.

   Apical dominance            

  Phototropism


The role of gibberellins

 

Gibberellins stimulate the following responses in plants:
- Stem elongation
- Root growth
- The germination of seeds
- Promotes flowering
- Fruit growth




FuseSchool - Global Education. (2017). Plant growth: auxins and gibberellins (CC BY)

 Seed germination

 Stem elongation

The role of abscisic acid

Abscisic acid stimulates the following responses in plants:

  • Is an inhibitor of growth
  • Causes plants to become dormant in winter
  • It causes abscission in leaves and fruit (they fall off the tree)
  • Lack of water (water stress) stimulates the production of Abscisic acid
  • Causes the closing of stomata when the plant wilts.

 Leaf fall

 Stomatal closing



                                     

Last modified: Friday, 26 March 2021, 6:43 AM