1. Plant Response to Stimuli other than Light
By:
Catherine Dombroski
Minki Beak
Aime Flores
Allea Cauilan

2. Gravity Gravitropism: a plant’s response to gravity
Roots: display positive gravitropism
Shoots: display negative gravitropism
Plants detect gravity by the settling of statoliths: specialized plastids containing dense starch grains
Located in the cells of the root cap
Thought to trigger redistribution of calcium → lateral transport of auxin
Some plants lack statoliths; their mechanism for detecting gravity:
Cells pull proteins and stretch them on the “up” side and compress them on the “down” side of the root cells
Dense organelles distort the cytoskeleton when they are pulled by gravity

3. Mechanical Stimuli
Thigmomorphogenesis: changes in form that result from mechanical disturbance
Rubbing stems of young plants a couple of times daily results in plants that are shorter than controls
Thigmotropism: growth in response to touch
Occurs in vines and other climbing plants
Action potentials: rapid leaf movements in response to mechanical stimulation
Transmission of electrical impulse
Sensitive Plant

4. Environmental Stresses
Abiotic: nonliving
Biotic: living
Abiotic/biotic factors: flooding, drought, extreme temperature, herbivory
Plant that cannot tolerate stresses will succumb or be outcompeted by other plants
Local extinction
Defenses for biotic factors (pathogens, herbivores, etc.)

5. Drought
Plants stressed by water deficiency → losing water through transpiration faster than it can be restored through the soil → kills plant
When there is a deficit of water, plant cells lose their turgor, which closes the stomata, slowing transpiration
The leaf also releases abscisic acid → closing stomata
Inhibits the growth of young leaves- decreases leaf surface
Wilting plant → leaves roll up to decrease leaf surface
During a drought, shallow roots stop growing & deeper roots continue to grow (to reach moist water sources)

6. Flooding
Over-watering a plant can suffocate it because the soil lacks air spaces which are used for cellular respiration in roots
Oxygen deprivation stimulates ethylene-
Causes some cells in the root cortex to undergo apoptosis
Destruction of these cells cause cells to create air tubes that function as “snorkels”, providing oxygen for submerged roots

7. Salt Stress Excess salt in soil threatens plants because:
1) Lowering water potential of soil solution
2) Sodium and other ions are toxic to plants when their concentrations are relatively high
Water potential becomes negative which reduces water uptake
Intake of harmful ions can be stopped, but that means less water intake

8. Heat Stress
Heat can kill plants by damaging and denaturing enzymes/damaging metabolism
Results in the closing of stomata → response to stress in order to prevent dehydration
Plants back-up response to heat is the synthesis of heat-shock proteins → help protect other proteins from heat stress
Chaperone proteins (chaperonins), unstressed cells help other proteins fold to their functional shape

9. Cold Stress
When temperature falls there is a change in the fluidity of the cell membranes
When membrane cools below critical point the fluidity is lost as the lipids lock in a crystalline structure which alters transport
Response is altering lipid composition of membranes
Cold= more stressful to plants because of the amount of time it takes for membrane modification
At lower temperatures, lipids increase proportions of unsaturated fatty acids which keep the membrane fluid by stopping crystalline formation