1. Plant Responses
Chapter 31

5. Section 1
Plant Hormones

6. Auxins

7. Apical Dominance

8. Apical Dominance

9. Gibberellins

10. Ethylene

11. Cytokinins

12. Section 2
plant movement

13. Tropism Tropism is a growth response
Positive tropism = growth toward stimulus
Negative tropism = growth away from stimulus

14. Phototropism – growth in response to light
Positive phototropism – toward it
Negative phototropism – away from it

15. Thigmotropism – growth in response to touch
Positive thigmotropism – toward it
Negative thigmotropism – away from it

16. Gravitropism – growth in response to gravity
Positive gravitropism – toward the source
Negative gravitropism – away from source

17. Chemotropism
Plant growth in response to a chemical

18. Nastic movements

19. Nastic Movements
Movements by a plant that are responding to a stimuli ( a tropism )
The direction they move is not important
no positive
no negative

20. Thigmonastic Response
A response to touch
Due to a drop in turgor pressure
Water pressure decrease – leaf evaporation

21. Thigmonastic Response
Venus flytrap
Prayer plant
Mimosa plant

22. Nyctinastic Response A daily response to light and dark cycle
Bean plant
Roses
Tulips

23. Section 3
seasonal responses

24. Photoperiodism
Plant response to seasonal changes in the length of day (or night)
Response is due to a pigment that is light sensitive
Affects:
flowering
dormancy start for buds
formation of storage organs

25. Day and Night Length A key factor in flowering
Many species have a “critical night length”

26. Day and Night Length Today – botanists use the phrases:
Short-Day plant (SDP)
Long-Day plant (LDP)
But the night length determines flowering

27. Short-Day Plants SDP flower when the days are short
This really means the nights are long
Those conditions occur only in the:
Spring and Fall

28. Long-Day Plants LDP flower when the days are long
This really means the nights are short
Those conditions occur only in the:
Summer

29. Seasonal Responses to Light
Type of Plant
Flowering
Conditions
Season
Examples
day-neutral plant
( DNP )
not affected by
day-night cycle
anytime spring to fall
tomatoes, dandelions,
roses, corn, beans
short-day
( SDP )
short days – LONG nights
spring, fall
ragweed, poinsettias, goldenrods, strawberries
long-day plant
( LDP )
long days – SHORT nights
summer
asters, irises

30. Fall Colors Changing fall color is due to photoperiodism
Change due to day length – temperature 

31. Fall Colors As nights become longer Leaves stop producing chlorophyll
Orange (carotenoids) and yellow (xanthophylls) become visible – by default

32. The End
Chapter 31