1. Plant responses to Internal and External Stimuli

2. Response  Stimulus Results in survival of species
respond by changing their growth pattern
Tropism – growth toward or away from a unidirectional stimulus, toward +, away -
Phototropism - light
Gravitropism - gravity
Thigmotropism – touch
Reception  transduction  response

3. Reception – Transduction - Response

4. Transduction – a multistep pathway that amplifies the signal
Reception – cell signals are detected by receptors that undergo changes in shape in response to specific stimulus.
Transduction – a multistep pathway that amplifies the signal
Response – accomplished by 2 mechanisms:
Turning genes on or off
Activation existing enzyme molecules

5. Plant Hormones
Chemical signals produced in very low concentrations for communication

6. Auxin affect many aspects of plant growth and development
Indoleacetic acid(IAA) most common occurring
Apical dominance – prevents lateral buds
Promotes root growth if applied
Promotes growth of fruit
Induce development of fruit without pollination
Weed control (Agent Orange)
Gravitropism and phototropism
moves to shady side, 2nd messengers lead to production of growth factors, elongation of stem on shady side, bends toward light

7. Ethylene
Involved in abscission, stimulates enzymes which cause leaves, fruit or flowers drop
Used to speed up ripening of fruit
Applied to citrus to keep color
Release gas at wound, speeds up ripening of fruit around fruit

8. Nastic movements
Movements that do not involve growth, not dependent on direction of stimulus
Seismonastic movements – touching, shaking, light or thermal stimulation
Mimosa plant, prayer plant
Changes in turgor pressure, K+
Circadian rhythm – biological rhythm with 24 hours cycle
Biological clock – mechanism by which the biological rhythm is maintained

9. Photoperiodism
Physiological response prompted by changes of length of day or night
Germination – breaking of bud dormancy
Can influence flowering
3 groups of flowering plants
Short day – day length 14 hours or shorter
Long day – 14 hours or longer
Day neutral - not dependent on day length
If dark period is interrupted, flowering will not result, not the same result if reversed

10. Photoperiodic control of flowering

11. Phytochrome blue/green leaf pigment, absorb red
has 2 forms that absorbs red light at different wavelengths
Phytochrome red – 660 nm
Phytochrome far-red – 730 nm
Allows a plant to detect photoperiod changes
Other functions of phytochrome
Promotes seed germination
Inhibits stem elongation

12. Plant defenses Thorns Chemicals such as bitter or poisonous compounds
Airborne attractants to recruit other animals to kill herbivores
Epidermal layer – protects against viruses by sealing off the pathogen and then killing the cells in the area – brown spots…