1. Plant hormones

2. Plant hormones compared to animal hormones
Similarities with animal hormones
organic
Signal molecules
Target cells are distant to the source
Differences to plant hormones
Don’t travel in general circulation
Are not produced by an endocrine gland
Are not polymers

3. Most cells in a plant are capable of making growth regulators/hormones
Small in size they can diffuse readily through the cell wall to influence nearby cells
Can transport through xylem or phloem to affect more distant cells

4. Auxin response in a plant cell

5. Types plant hormones/growth regulators
Plant growth regulator
Produced in
Transport in plant
effects
Auxins
Apical tip
Young leaves
Tip to base through parenchyma cells
Stimulates cell elongation, cell division in the cambium and differentiation of phloem and xylem
Trophic response to light and gravity
Suppress growth of lateral buds
Delay leaf senescence and fruit ripening: stimulates growth of flower parts
Gibberellins
Young leaves, roots, shoots and embryo seed
Xylem and phloem
Promotes cell division and elongation in plant shots
Extend internodes and can rise flower heads
Cytokinins
Roots
xylem
Stimulate cell division and the middle layer of cells in leaves.
Tend to concentrate starch in seeds and young fruit
Abscisic acid
Older leaves, root cap and stem
Vascular tissue
Generally acts as an inhibitor
Promotes the closer of the stomata(especially in water stress
Stimulates dormancy in seeds and buds
ethylene
Stems, ripening fruit, damaged and senescing tissue, seeds
Diffusion throughout intercelluar space
Promotes fruit ripening, leafs fall, senscences(plant aging) and stress response

6. Tropism in plants
Phototropism – respond to light by growing towards the light
Geotropism – respond to gravity
Negative shoots grow upwards
Positive roots grow down
Photoperiodism – responds to change in day length or change of season
Vernalisation – responds to periods of cold
Thigmotropism – climbing plants to wrap themselves around a support
Heliotropism – plants to follow the sun during the course of the day

7. Phototropism Stimulus light receptor transmission Response
effector
Response
Grow to light

8. Plant life cycle Life cycle event Hormones involved
Environmental factors involved
Germination of a seed
Abscisic acid concentration decreases
Gibberellin and ethylene increases
Seed dormancy broken by swelling with water
Length day and night
Long period of prolonged cold
Physical damage to seed coat(may pass through animal gut)
Growth to a mature plant
Auxins - geotropism response
Gibberellin promotes elongation and cell division
Cytokinins – cell division
Gravity – negative and positive geotropism
Avaliabilty of light and water
Winter dormancy
Increase of ethylene – promotes leaf drop
Increase abscicis acid – stops budding/shots growing
Lengthening nights
Flowering
Gibberellins(in some species)
Ethylene (in other species)
Photoperiodism
Some require long nights to initiate
Some require prolonged cold periods
Some require shorter nights
All depends on the time of year it flowers
Fruit development
Auxin and gibberellins promote fruit growth
Some light is required for fruit development
Seed dormancy
Abscisics acid – prevent germination
Until correct germination conditions are reached

9. Ripening a tomato

10. Plant flowering response to red light

11. Gibberellins and auxins especially