Topic 12 - Plant Control Systems & Behaviour Flashcards
1
Q
Plant Hormones
A
- Plant hormones (plant growth regulators) are chemical signals that modify or control one or more specific physiological processes
- They are produced in very low concentrations, but can have profound effects on growth and development
- Plant hormones are mobile throughout the body of the plant
2
Q
Hormonal Responses to Stimuli
A
- Many long-term responses are mediated by chemical signals = plant hormones
- Produced in active growth regions
- Auxin (Indolacetic acid, IAA)
- Cytokinins
- Gibberellins (GAs)
- Abscisic acid
- Ethylene
3
Q
Auxin
A
- Compounds that promote cell elongation
- Produced in shoot apical meristems & leaf primordia
- Root apical meristem = very little!!
4
Q
Auxin Functions
A
- Growth responses (cell elongation)
- Phototropism
- Gravitropism
- Pattern development
- Branching pattern
- Phyllotaxy
- Promotes lateral roots
5
Q
Acid-Growth Hypothesis
A
- Membrane proton pumps
- Cell wall acidification
- Expansin activation
- Separation of microfibrils
- Wall enzyme activation
- Cleavage of crosslink polysaccharides
- Cell wall loosening
- Turgor pressure > wall Pressure
6
Q
Phototropism
A
- Shoots: positive
- In grasses:
1. Shoot apical meristem
2. Auxin redistribution- Lateral transport to the shady side
- Unequal cell elongation
- Stem bends
- Lateral transport to the shady side
7
Q
Gravitropism
A
- Positive or Negative
- Statoliths
- Dense starch granules in the root cap
- In a horizontal settle
1. Statoliths settle- Cytoskeletal distortion
- Auxin redistribution
- Lateral transport to the storage side
- Growth Inhibition
- Cytoskeletal distortion
8
Q
Cytokinins
A
- Compounds that stimulate cell division.
- Produced in:
- Root apical meristems
- Embryos & fruit
- Cell division at meriistems
- Cytokinesis
- Cytokinin:auxin ratio
- Callus
- More cytokinin - shoots develop
- More auxin - roots develop
9
Q
Apical Dominance
A
- A balance of two hormones
- Auxin gradient
- Produced in the terminal bud(s)
- Cytokinin gradient
- Produced in the roots
- Removal of shoot apical meristem
- Axillary bud activation
- Addition of auxin after cutting?
10
Q
Gibberellins
A
- Compounds that stimulate fruit growth, stem elogation, and germination
- Roots & young leaves
- Fruit growth
- Stem and leaf growth
- Cell wall loosening
- Foolish rice & bolting cabbage
11
Q
Gibberellins and Germination
A
- Seed imbibes
- Dormancy breaks
- Gibberellins (GA) produced by embryo
12
Q
Abscisic Acid
A
- Slows growth
- Seed dormancy
- Maintained by abscisic acid
- Imbibition washes
- Embryo development
- Drought tolerance
- Stomata closing
- Guard cell K+ channels open
13
Q
Ethylene
A
- Gaseous growth regulator in response to stress
- Ethylene from coal gas
- Also produced in fruit
- Stress responses
- Drought, physical pressure, injury
- Induced by auxin
- Senescence
- Programmed death
- Fruit Ripening
14
Q
Mechanical Stress
A
- Triple Response
- Growth into an obstacle
- Ethylene production
- Shoot tip
- Morphological changes
- Obstacle avoidance
- Concentration dependent effect
- Normal growth resume
15
Q
Senescence
A
- Autumnal leaf abscission
- Balance between auxin & ethylene
- ion reclamation
- Stored in parenchyma
- New pigments and old
- Auxin concentration
- Sensitivity to ethylene
- Cell wall breakdown
- Cork layer
- Leaf scar
