Transcript Chapter 38 Control of Plant Growth and Response

Chapter 26
Control of Plant Growth
Responses in Flowering Plants
Read Ch 26 in Textbook
Read pg 210-214 in Cliffs AP Book
Mills AP Bio 2003/2013
Chapter 26
Control of Plant Growth Responses in Flowering Plants
Overview
• Topics
– 26.1 Plant Hormones
– 26.2 Plant Responses
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.1 Plant Hormones
• Mechanism of action – hormones
– Receptor
– Transduction pathway
– Cellular response
Mills AP Bio 2003/2013
Second Messenger Animation
Mills AP Bio 2003/2013
• Groups of Plant Hormones
–
–
–
–
Auxins
Gibberellins
Cytokinins
Inhibitory hormones
– Hormones work together to cause various effects
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.1 Plant Hormones
• Auxins
– Most common auxin is
indoleacetic acid(IAA)
– Prevent growth of axillary buds
 supports apical dominance
– Promotes adventitious root
growth (roots from stem)
– Promotes root branching
– Auxins produced by seeds
promote growth of fruit. If
auxins high in fruits and low in
stems and leaves, fruit won’t
fall off.
– Promote phototropism and
gravitropism
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.1 Plant Hormones
• How Auxins work
–Auxin binds to receptors on cell membrane
–Activates ATP driven proton (H+) pump
–Pumps H ions into space between cell membrane and cell wall.
–H ions (acid) weaken cell wall.
–Gradient set up that pulls solutes then water into cell causing it to swell
–Pushes on cell wall
–Cell elongates
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.1 Plant Hormones
• Gibberellins
– About 70 different
gibberellins, GA3 the
most common
– Promote stem elongation
especially in dwarf plants
– Can break dormancy in
seeds and buds
– Sources: young leaves,
roots, embryos, seeds,
fruits
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.1 Plant Hormones
• How Gibberellins work
– Gibberellin binds to a
receptor on the cell
membrane
– Activates a second
messenger inside the cell –
Ca++
– Ca++ combines with a
protein called calmodulin
– This complex activates the
gene that codes for
amylase
– Amylase acts on starch to
release sugars
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.1 Plant Hormones
• Cytokinins(remember cytokinesis?)
– Derivatives of adenine
In tissue culture:
• Zeatin
Auxin and cytokonins in
• –Kinetin
usual amounts
tobacco strip develops
into undifferentiated
callous.
If ratio of auxin to
cytokinins is appropriate,
the callous produces
shoots.
A different ratio
– Promote cell division and differentiation
promotes vegetative
shoots and leaves.
– Prevent senescence (aging process)
A different ratio
promotes floral
shoots.
• In senescence, large molecules in the plant are broken down
• Can lead to leaf loss etc
• Cytokinins inhibit leaf death and can promote leaf growth
– Varying ratios of cytokinins and auxins can effect how plant
differentiates
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.1 Plant Hormones
• Inhibitory Hormones
– Abscisic acid (stress hormone)
• Promotes bud and seed dormancy
• Closes stomates(when water supply
low) by causing K+ to leave guard cells
• Inhibits gibberellins (which break
dormancy)
• Produced by any “green tissue” with
chloroplasts, by endosperm and by
roots.
• Abscission=dropping of leaves, fruit
and flowers from plants
– Originally thought that abscisic acid
caused this – now believe it is ethylene
– Ethylene
• Induces leaf, flower and fruit abscission
(falling off)
• Promotes fruit ripening-increases
activity of enzymes that soften fruit (ex.
cellulase)
• Gas released from fruit (wound?)
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.1 Plant Hormones
Functions of Plant Hormones
Hormone
Function – all of these hormones work together
Auxins
Stimulate growth
Involved in stem and root cell elongation in phototropism and gravitropism
Gibberellins
Stimulate growth especially stems, especially in dwarf plants.
Can break seed and bud dormancy
Cytokines
Stimulate growth by causing cell division
Abscisic Acid
Inhibit growth
Causes stomates to close
Maintains seed and bud dormancy
Ethylene
Inhibit growth
Causes fruit to ripen and fall
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• 38.1 Plant responses
– Tropisms
– Nastic movements
• Tropisms
– Plant growth toward (positive) or away (negative) from a stimulus
– Receptiontransductionresponse
– Common tropisms
• Phototropism
• Gravitropism
• Thigmotropism
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• Phototropism
– Cells on dark side of plant
grow faster, so plant bends
toward the light – positive
phototropism
– Pigment related to
riboflavin acts as a receptor
which somehow causes the
release of the hormone
auxin, which migrates to the
shady side, causing
increased growth.
– Auxin is produced in the
Phototropism short clip:
shoot tips
..\..\Biology\Biology Clipart Movies Animations Sounds\Biology
movies\phototrop1.2[1].mov
– Roots are either insensitive
to light or show negative
phototropism
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• Gravitropism
– Roots show positive
gravitropism
• If root cap removed, root
doesn’t respond to gravity
• Statoliths in cap
– Stems show negative
gravitropism
– Auxin moves to lower side of
stem or root in response to
gravity (may be newer theories)
Section of pea root, showing
• Auxin inhibits growth of root
statoliths settled at bottom of cells
cells on lower side  root
grows down
• Stimulates growth of stem
Gravitropism(negative) in stems movie.
cells on lower side  stem
Time lapse/actual time 1 hour:
..\..\Biology\Biology Clipart Movies Animations
grows up
Mills AP Bio 2003/2013
Sounds\Biology movies\gravitropism.mov
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• Thigmotropism
– Unequal growth due
to contact with a
solid object
– Cells opposite the
side being touched
elongate
– Hormones auxin and
ethylene may be
involved.
Thigmotropism movie – Pictures taken at 10 min intervals– morning glory vine grows:
..\..\Biology\Biology Clipart Movies Animations
movies\Thigmotropism vine
Mills AP BioSounds\Biology
2003/2013
winding.mov
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• Nastic Movements
– Independent of direction of
stimulus
– Types
• Seismonastic movements
– Respond to touch, shaking or
thermal
» Ex: Mimosa – sleeping
grass, Venus flytrap
• Sleep movements
– Occur daily in response to light
and dark changes
» Ex: Prayer plant – folds
Mimosa plant after being touched
up at night
– Rhythmic sleep behavior =
..\..\Biology\Biology Clipart Movies
Circadian rhythms
Animations Sounds\Biology movies\nastic
sensitive_plant_open[2].avi
– Circadian rhythms can persist
even without the stimulus d/t
biological clocks Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
•
Greenhouse-grown plants were placed in continuous light. The diurnal
opening/closing of the leaflets (nyctinasty) is clearly observed.
– Nastic movement over time movie
– Also (nyctnasty in silk plant)
http://employees.csbsju.edu/ssaupe/images/Movies/silk_tree.avi
– From http://employees.csbsju.edu/ssaupe/biol327/Lab/movie/movies.htm
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• Nastic Movements-how
they work
– Stimulus causes K ions to
move out of a specialized
area of cells (pulvinus) at
base of leaf.
– Water follows by osmosis
 decreased turgor
Trigger
Hairs
pressure.
– Stimulus on one leaf can
cause other leaves to
close, so must have some
system of communication.
Three sensitive trigger hairs on each leaflet
Venus Flytrap movies:
..\..\Biology\Biology Clipart Movies Animations
Sounds\Biology movies\venus flytrap movie.mov
..\..\Biology\Biology Clipart Movies Animations
Sounds\Biology movies\Venus Fly Trap.wmv
..\..\Biology\Biology Clipart Movies Animations
Mills AP Bio 2003/2013
Sounds\Biology movies\Venus flytrap eating a spider.wmv
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• Photoperiodism
– Physiological
responses brought
about by changes in
the length of day or
night.
• Three plant groups
– Short-day plants
• Flower when the day length is
shorter than a critical length.
– Long-day plants
• Flower when the day length is
longer than a critical length.
– Day-neutral plants
• Flowering not dependent on
day length.
– Plant flowering actually
depends on a critical length of
darkness.
– Short days correspond with long
nights.
Kolonchoe –
short day plantMills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
If light at least critical length or shorter flowers
More accurate:
If light at least critical length or longer flowers
26.2 Plant Responses
More accurate:
If dark at least critical length or longer (regardless of
length of light) and continuous flowers
If dark at least critical length or shorter (regardless of
length of light) flowers
flash of light during dark will inhibit flowering
If critical darkness longer than critical length, but
interrupted by a flash of light, flowering will occur.
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• Phytochromes
– Theory: pigment molecules that detect photoperiods, and
directs flowering of plants
– Blue green leaf pigments that exist in two forms:
• Pr – phytochrome red (inactive form) – absorbs red light
660mm wavelength – gets converted to Pfr
• Pfr – phytochrome far red (active form) – absorbs red light
730nm – gets converted to Pr
– Sunlight has more red than far red wavelengths, shade and
sunset have more far red wavelengths
• So in sunlight, Pr absorbs red light and gets converted to Pfr,
which is the active form and induces flowering etc.
– Phytochrome conversion may be the first step in reception
transduction  reaction pathway?
Mills AP Bio 2003/2013
Phytochrome Animation
Mills AP Bio 2003/2013
Chapter 26 Control of Plant Growth Responses
26.2 Plant Responses
• Phytochromes – other functions
– Pr  Pfr (in sunlight)
• Promotes seed germination, leaf expansion, stem branching, and inhibits
stem elongation
– Presence of Pfr tells some seeds that conditions are right for
germination
• Some seeds need dark to germinate, some do better with some light
– In presense of more far red (shade), Pfr increases, leading to shade
avoidance strategies – stem elongation, flowering to produce seeds
Mills AP Bio 2003/2013
The End
Mills AP Bio 2003/2013