Transcript Control Systems in Plants

Control
Systems
in Plants
Etioloation
and
Deetiolation
Plant Hormones
• What is a Plant hormone?
• Compound produced by one part of an
organism that is translocated to other
parts where it triggers a response in
target cells and tissues.
Experiments on Phototropism
Discovery of Hormones
• 1. Darwin and Darwin
– Removed the tip of the coleoptile of a grass
seedling, and it failed to grow toward light.
• 2. Boysen-Jensen
– Put block of gelatin on coleoptile tip to allow
chemical diffusion
– Auxin purified later by Thimann
• 3. Went
– Modified Boysen-Jensen experiments
– Extracted the chemical messenger responsible
Functions of Plant Hormones
• Control plant growth and development by
affecting division, elongation, and cell
differentiation
• Effect depends on size of action, stage of
plant growth and hormone concentration
• Hormonal signal is amplified by gene
expression, enzyme activity, or membrane
properties
Five Classes of Plant
Hormones
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Auxins
Cytokinins
Gibberellins
Abscissic acid
Ethylene
Which hormones cause the following….
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Apical dominance from apical bud
Abscission
Stimulates growth of axillary buds
Root growth
Stimulates closing of stomata
Causes fruit ripening
Stimulates seeds to break dormancy and
germinate
Growth inhibitor
Cell division and differentiation
Cell elongation
Seedless fruit
Which hormone is made at each
location?
• Made in roots and transported upwards
• Found in meristems of apical buds and
seed embryos
• Found in tissues of ripening fruit
• Leaves stems, roots and green fruit
Which
hormone
caused
the
following?
Opposing hormones
• Which two hormones act in opposition
to one another regarding apical
dominance, cell division and
differentiation?
• Which two hormones work in opposition
regarding seed dormancy?
Phototropism
Acid
Growth
Hypothesis
Plant Movement
• A. Tropisms:
– growth response
toward or away from
stimuli
• 1. Phototropism
– cells on darker side of
shoot elongate faster
than cells on bright side
due to auxin distribution
– auxin move laterally
across the tip from the
bright to dark side by an
unknown mechanism.
– Cells on the dark side
grow
• 2. Gravitropism
(geotropism)
– gravity
– roots --> positive
geotropism
– stems---> negative
geotropism
• Statoliths
– starch grains in root cap
cells, they trigger calcium
redistribution which
results in auxin
movement in root
– auxin inhibits cell
elongation
– upperside of root
elongates faster than
bottom
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3. Thigmotropism
growth in response to touch
tendrils contacts solid and coils
increased production of ethylene
• 4. Hydrotropism
• growth toward water
• willow tree
Circadian Rhythms and the
Biological Clock
• Circadian Rhythm- a physiological cycle
with a frequency of about 24 hours that
persists even when an organism is
sheltered from environmental cues.
• Photoperiodism
– a physiological response to DAY length
– seasonal events
• Photoperiods Control of Flowering
– the amount of night length controls
flowering
• 1. Short day plants
– late summer, fall and winter
• 2. Long day plants
– late spring and summer
• 3. Day- Neutral plants
– unaffected by photoperiods
Critical Night Length
• Night (dark) actually causes flowering
not light
– Leaves detect the photoperiod while buds
produce flowers
• Florigen– scientists believe this unidentified hormone
is produced in the leaves and moves to
buds.
Phytochrome
• Protein containing chromophore (lightabsorbing component) responsible for a
plant’s response to photoperiod
– Pr - red absorbing
– Pfr- Far red absorbing
• Plants synthesize Pr in dark
– if phytochrome illuminated then Pr
both types of light are seen
Pfr since
• Pfr triggers many plant responses to light
• In darkness Pfr goes back to Pr
Response to Stress
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Water deficit
Oxygen deprivation
Salt Stress
Heat Stress
Cold Stress
Herbivores…
Defense Against Pathogens
• Gene for Gene relation between plant
and pathogen
• Coevolution between plant and
pathogen
Short Day Plant
Short Day Plant
• Spinach Long Day Plant
Spinach Long Day Plant
Which
wavelength of
light
causes
phototropism?
Auxins
IAA indoleactetic acid: natural
auxin
• Promotes elongation & secondary
growth
• Apical meristem is the major site of
auxin production
• Inhibits lateral growth
• Induces female floral parts & fruit
Cytokinins
• Move from the roots to tissues by moving up
xylem
• Works with auxin to promote differentiation
• Stimulates protein synthesis
• Made in roots
• Function:
– 1. Cell division and differentiation
– 2. Apical dominance
– 3. Anti-aging hormones
• slow protein deterioration
Observe Apical Dominance
Gibberellins
• Stimulate elongation of cells
• Inhibits root growth
• Stimulate flower part developmentbolting(large internode)
• Works with auxin for fruit development
• Signals seeds to break dormancy and
germinate
Abscisic Acid (ABA)
• Growth inhibitor
• returns seeds to dormancy
• inhibits cell division in vascular
cambium
• causes rapid closing of stoma during
dry periods
• promotes positive geotropism
Ethylene
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Gaseous hormone
high [auxin] induce release of ethylene
fruit ripening (positive feedback)
Apoptosis:
– Senescence (aging)
– Abscission
– leaves falling