1. External factors and Plant growth
Chapter 28
External factors and Plant growth

2. Nastic Movement
Nastic Movements- plants movement that occur in response to a stimulus independent of position of stimulus ( leaves light and dark cycle)
Phototropism- response to light- caused by elongation- under the influence of Auxin
Gravitropism- response to gravity
Thigmotropism- response to touch

3. External Factors and Plant Growth
Tropism- the growth response involving bending, or curving, of a plant part toward or away from an external stimulus determines the direction of movement

4. Went’s experiment- chemical produced by growing tips influences direction of growth

5. What role does the light play in the phototropic response?
Light decreases the auxin sensitivity of the cells on the lighted side
Light destroys auxin
Light drives auxin to the shaded side
‘Light eliminates auxin activity’
Tropism video

6. Gravitropism- starch-statolith plastids hypothesis

8. Auxin and root gravitropism

11. Gravitism video

12. Thigmotropism is growth in response to touch
Tendrils of bur cucumber
Enables shoots and roots to navigate, cling and climb
Thigmotropism in Opuntia acanthocarpa flowers video

13. Thigmotorpism- tendrils of
bur cucumber, twisting
Caused by different growth
Rates on the inside and
Outside of tendril

14. Phototropism
Common response to light

15. Diurnal movements of Wood sorrel (Oxalis)

16. Diurnal movement- biological clock is the organism
keeping itself in time with some external stimulus?

17. Other types of Movement
Thigmonastic (seismonastic) Movement are results of mechanical stimulation
Most night closure (nyctinastic movement) are results from changes in the size of perenchyma cells in the jointlike thickening (pulvinus) structure at the base of each leaf.

18. Pulvini Mimosa pudica vascular tissue surounded
By a cortex which consists largely of thin-walled
Parenchyma cells

19. Mimosa pudica

20. Entire leaf drops in response
To movement, shock, thermal
Stimulation, touch
Results from changes in turgor
Pressure in pulvini

21. Touch reponse in the venus flytrap (Dionaea muscipula)

22. Thigmomorphogenesis- The inhibition of growth by touch Arabidopsis thaliana both six weeks of age

23. Solar tracking Lupine (Lupinus arizonicus)

24. Sunflower solar tracking