Download Regulation of Plant Function

Plant Response to
Stimuli
Chapters 39
What you need to know!
• The 3 steps to a signal transduction
pathway.
• The role of auxins in plants.
• The survival benefits of phototropism and
gravitropism.
• How photoperiodism determines when
flowering occurs.
Signal Transduction Pathway
Organismal responses to stimuli involve a
cascade of cellular interactions:
1.Reception: cells detect signals when
ligands bind to specific receptors which
change shape in response
–
Gprotein
2.Transduction: amplification of response
allowing for small number of molecules
(hormones) to trigger a large response
3.Response: Cell responds to specific stimuli
by:
1. Increasing or decreasing mRNA production, or
2. Activating existing enzyme molecules.
Signal Transduction Pathway
Hormones
• Hormones are chemical messengers that
allow coordinated cellular responses; they
are produced by one part of the organism
and transported to another
Tropism is a hormonal plant growth response
toward or away from a stimulus
• Phototropism: positive or negative growth
toward or away from light
• Gravitropism (growth parallel to gravity)
• Thigmotropism (detect support structure)
Phototropism
Gravitropism
Hormones in Plants
Name
Auxins
Function
Early plant growth; elongation of root
and shoot
Ethylene
(gas)
Apoptosis (leaves, flowers), fruit
ripening (positive feedback loop)
Cytokinin
Stimulates germination and
plant growth
Gibberilin
Works in concert with auxins in stem
elongation, germination
Abscisic
Acid (ABA)
Inhibits growth, maintains
dormancy, closes stomata
during water stress
Plant Responses to Light
• Light is critical for plant success
• Light receptors (phytochromes) detect
specific wavelengths of light
– Triggers plants development
• Photoperiodism is a response to the length
of day/night
– Short-day plants (long-night) flower in early
spring or fall
– Long-day plants (short-night) flower in late
spring or early summer
– Day-neutral plants flower in any day length
• Circadian rhythms are physiological cycles
of about 24 hours (not dependent on light)
Plant Defensive Responses
Herbivore Defense:
•Thorns
•Distasteful and/or poisonous chemicals
•Airborne attractants draw predators
Bacterial and Viral Immune Response
•First line of defense = epidermal layer
•Second line of defense =
1. recognition of pathogens
2. Develop resistance or isolate infected area
3. Deliver resistance throughout plant or
apoptosis
Mimosa Plant Reacting to
Herbivores