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Botanik 1
• Föreläsning 080513
• Johan Edqvist
• [email protected]
Gibberelliner (GA)
Fler än 125 olika
gibbereliner har
identifierats
Tetracykliska
terpenoider
Gibberelliner (GA)
Upptäcktes av japanska forskare på 1920-talet
Risplantor som blev tokigt långa ”bakanae eller
foolish seedling disease” efter infektion av svampen
Giberella fujikoroi.
1958 isolerades GA från rosenbönan Phaseolus coccineus.
GA
GA syntetiseras via
Terpenoid pathway.
Innehåller syntessteg i
plastider, ER och cytosol.
Gibberelliner (GA)
Syntes av GA sker i många olika vävnader
Gibberelliner (GA)
Fenotyper hos
Arabidopsis
plantor med
mutationer vid
olika steg av GA
syntesen.
Gibberelliner (GA)
Stimulerar tillväxt
GA stimulerar både
celldelning och
cellelongering
Dvärgmutant
Gröna revolutionen
60- o 70-talet
Ris, vete
Dvärgmutanter
+Gibberellin
Gibberelliner (GA)
GA stimulerar både
celldelning och
cellelongering
Tillsats av GA
påverkar
dvärgmutant
men inte
vildtyp.
Gibberelliner (GA)
GA3 kan inducera bolting
och blomning i kål
Gibberelliner (GA)
Påverkar
fruktutveckling
Thompson Seedless
+Gibberelin (GA3)
Gibberelliner (GA)
Reglerar frövila och frögroning
GA 100 pp miljard
GA 1 pp miljard
Vatten
Gibberelliner (GA)
Reglerar frövila och frögroning
korn
GA verkar i aleuronelagret
Samspel mellan GA och ABA
Tobak
Brassica
Styr frövila och frögroning
Samspel mellan GA och ABA
Styr frövila
och
frögroning
Gibberelliner (GA)
Gibberelliner (GA)
Gibberelliner (GA)
A tropism is a biological phenomenon, indicating
growth or turning movement of a biological
organism, usually a plant, in response to an
environmental stimulus.
Types of tropisms
Chemotropism: in response to chemicals
Geotropism or Gravitropism: in response to gravity
Hydrotropism: in response to moisture or water
Heliotropism: in response to sunlight
Phototropism: response to light
Thermotropism: to temperature
Thigmotropism: in response to touch or contact
Phototropism
Phototropism
Phototropism
Blue-light 400-500 nm
Phototropism
Expression of the DR5::GUS reporter in hypocotyl of
untreated (a) or auxin efflux inhibitor (NPA)-treated (b)
wild-type seedlings upon stimulation by light (a, b)
Friml et al (2002) Nature 415: 806-809
Phototropin
Ingen phototropism i nph-mutanter
nph: non-phototrophic hypcotyl
NPH= photoreceptor phototropin
(Phot1)
Liscum & Briggs (1995) Plant Cell 7, 473-485
Phototropin
Nph1(Phot1) undergoes
autophosphorylation and
functions as a photoreceptor for
phototropism
NPH photoreceptorn phototropin är ett plasmamembran
associerat phosphoprotein med massan 120kD.
Phototropins are blue-light receptors controlling a range of responses
that serve to optimize the photosynthetic efficiency of plants.
Liscum & Briggs (1995) Plant Cell 7, 473-485
Phototropin
Phot1 & Phot2 har
överlappande
funktioner
Annual Reviews
Phototropin
Light drives the formation of a
covalent adduct between the
FMN chromophore and a
conserved cysteine residue within
the LOV domain.
In darkness, the FMN chromophore is
noncovalently bound within the LOV
domain, forming a species that
absorbs maximally at 447 nm
(LOV447). Light drives the production
of a highly reactive triplet-state flavin
(LOV660) that leads to formation of a
covalent bond between the C(4a)
carbon of the FMN chromophore and
a conserved cysteine residue within
the LOV domain (LOV390).
Annual Reviews
Phototropin
Expression of the
phot1-GFP Fusion
Protein in 3-DayOld Etiolated
Seedlings.
Sakamoto & Briggs (2002)
Plant Cell 14: 1723-1735
Gravitropism
Root gravitropism
Perception of gravity is correlated with sedimentation of amyloplasts
Root cap
Columella cells from root cap
Amyloplast: Starch-containing non-pigmented plastids
Columella cells
Amyloplasts and gravity
Starch-statholith hypothesis: amyloplasts=gravity sensors
Gravitropism
Starch-statholith hypothesis: amyloplasts=gravity sensors
Protoplast pressure hypothesis: The weight of the
entire protoplast changes the gravity perception of
the plant.
Tensegrity model (tensegrity = tensional integrity): The
interaction of falling amyloplasts with the structural
integrity of the cell is responsible for gravitropism. Actin
filaments form a structural meshwork anchored to the
plasma membrane. The amyloplasts create tension
which leads to disruption of the actin meshwork.
Because actin tension affects calcium channels on the
plasma membrane, we expect a transient increase in
cytosolic Ca2+ level.
Auxin and root
gravitropism
Assymetric distribution of auxin
Growth inhibition on lower side
of root
Gravistimulation results in asymmetric auxin
accumulation in lateral root cells
Auxin and root
gravitropism
PIN3-auxin
efflux carrier
Efflux: something
that flows out
b, c, pin3 hypocotyls are
defective in gravitropic (b) as
well as phototropic (c)
responses. Scale bars, 500 m. d, pin3 mutants are
defective in root
gravitropism. Each
gravistimulated root was
assigned to one of twelve 30°
sectors. The length of each
bar represents the
percentage of seedlings
showing direction of root
growth within that sector.
Friml et al (2002) Nature 415: 806-809
Gravitropism
Cytokinin and root gravitropism
GUS reporter gene
Symmetrical
distribution of cytokinin
Asymmetrical distribution of cytokinin
Circadian rythms
Regular rhythms of growth and activity, which occur in an
approximately 24-hour cycle
day
night
Diurnal movements
Controlled internally-the biological clock
Circadian rythms
Fig. 1. The circadian system has a regulatory role in nearly all aspects of a plant's life. (A)
Germination, (B) hypocotyl elongation, (C) leaf movements, (D) circumnutations, (E) shade
avoidance, (F) flowering time, (G) flower opening, (H) scent production, (I) tuberization, (J)
winter dormancy, (K) stomatal opening, (L) photosynthesis, (M) photoprotection, and (N)
protection from temperature extremes.
Environmental signals: zeitgeibers
Free-running
Suspension of
circadian
rhytm
Restart
PHY (phytochromes) red-light-sensing
CRY (cryptochromes) blue-light-sensing
Figure 1 Schematic representation of circadian clock structures
PHY (phytochromes) red-light-sensing
CRY (cryptochromes) blue-light-sensing
Biochemical Journal
www.biochemj.org
Biochem. J. (2006) 397, 15-24
Circadian oscillator
Light at dawn activates LHY and CCA1
LHY and CCA activates LHCB and other morning genes
LHY and CCA repress TOC1 and other evening genes
Circadian oscillator
Reduction of LHY and CCA1 during the day allows increase in TOC1-levels
TOC1 stimulates expression of LHY and CCA1
The circadian clock of
Arabidopsis has an
intrinsic period of
between 22 and 29 h,
depending on plant
accession and growth
conditions.
Consequently, the clock
mechanism is reset each
dawn and/or dusk to
prevent the clock
becoming increasingly
desynchronized with the
external light/dark
cycles.
CCG: circadian clock genes
Figure 4 Model of the Arabidopsis circadian clock
PHY (phytochromes) red-light-sensing
CRY (cryptochromes) blue-light-sensing
Biochemical Journal
www.biochemj.org
The circle around the
model indicates time
of day, with 0
representing dawn.
Components are
positioned within the
circle according to
their approximate
maximal transcript
abundance in
continuous light, with
the exception of LKP2
and ZTL which are not
transcribed in a
circadian-dependent
manner [105,108] and
thus are represented
by hexagons.
Biochem. J. (2006) 397, 15-24
CIRCADIAN CLOCK ASSOCIATED 1 (CCA1)
Wang and Tobin (1999) Cell 93: 1207-1217
CIRCADIAN CLOCK ASSOCIATED 1 (CCA1)
Wang and Tobin (1999) Cell 93:
1207-1217
Correct circadian period enhances growth and survival.
Dodd et al (2005)
Science 309: 630 - 633
ztl-1 [= 27.1 hours–32.5 hours]
toc1-1 [= 20.7 hours]
Correct circadian
period enhances
growth and
survival.
ztl-1 [= 27.1 hours–32.5 hours]
toc1-1 [= 20.7 hours]
Dodd et al (2005)
Science 309: 630 - 633
Photoperiodism
Daylength and flowering
Photoperiodism
LDP: Blommar när
daglängden överskrider en
viss kritisk längd
SDP: Blommar när
daglängden är kortare
än en viss kritisk längd.
Photoperiodism
Gullfrö
Light period shorter
than a critical length
Bolmört
Light period longer
than a critical length
22,5C: 10h 20min
Photoperiodism
Short-day
Long-day
Chrysantemum
Short-day plant
Short-day
Long-day
Spinach
Long-day plant
Photoperiodism
Photoperiodism
Red light
Red light
Red light
Far-red light
Red light
Far-red light
Red light
Far-red light
Red light
Far-red light
Phytochromes: red-light receptors
Red light induces germination
Far-red light prevents germination
Phytochromes: red-light receptors
Pfr=Biologically active
Present in two forms (Pr (r=red) and Pfr (fr=far-red))
with different absorption spectra
Phytochrome
Pfr=Biologically active
Phytochrome
Phytochrome chromophore (Pr form)
Phytochrome
Phytochrome
Phytochrome
Phytochrome
Fotomorfogenes
Thigmotropism
Growth in response
to touch
Thigma is the
Greek word for
touch
Thigmonastic movements
Mimosa pudica
Touch response
Nastic movement: Movement that is caused by an external stimulus, such
as light or temperature, but is directionally independent of its source, unlike
tropisms.
Nastic movement: Movement that is caused by an external stimulus, such
as light or temperature, but is directionally independent of its source, unlike
tropisms.
Thigmonastic movements – mechanical stimulation
Nyctinastic movements - sleep movements
Changes in turgor pressure
Turgor pressure or turgidity is the pressure of the
cell contents against the cell wall, in plant cells,
determined by the water content of the vacuole,
resulting from osmotic pressure.
Nastic leaf movements
Changes in
size of the
parenchyma
cells in the
pulvinus
Changes in turgor pressure
On receiving the action potential signal, the cells in the lower half of the
pulvinus respond by expelling potassium and chlorine ions and taking up of
calcium ions. This results in an osmotic gradient that draws water out of the
affected cells. The lower pulvinus cells temporarily shrink due to water loss.
This forces the entire structure to curve down in the manner of a fan. In this
contracted position, the pulvinus no longer functions as a support and the
petiole droops.
Thigmonastic movements
Thigmonastic movements
Nastic movement: Movement that is caused by an external stimulus, such
as light or temperature, but is directionally independent of its source, unlike
tropisms.
Thigmomorphogenesis
Untouched
Touched