External factors and Plant growth Chapter 28 External factors and Plant growth
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
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
Went’s experiment- chemical produced by growing tips influences direction of growth
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
Gravitropism- starch-statolith plastids hypothesis
Auxin and root gravitropism
Gravitism video
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
Thigmotorpism- tendrils of bur cucumber, twisting Caused by different growth Rates on the inside and Outside of tendril
Phototropism Common response to light
Diurnal movements of Wood sorrel (Oxalis)
Diurnal movement- biological clock is the organism keeping itself in time with some external stimulus?
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.
Pulvini Mimosa pudica vascular tissue surounded By a cortex which consists largely of thin-walled Parenchyma cells
Mimosa pudica
Entire leaf drops in response To movement, shock, thermal Stimulation, touch Results from changes in turgor Pressure in pulvini
Touch reponse in the venus flytrap (Dionaea muscipula)
Thigmomorphogenesis- The inhibition of growth by touch Arabidopsis thaliana both six weeks of age
Solar tracking Lupine (Lupinus arizonicus)
Sunflower solar tracking