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Chapter 39
Plant Responses to Internal
and External Signals
Overview: Stimuli and a Stationary Life
• Linnaeus noted that flowers of different species
opened at different times of day and could be
used as a horologium florae, or floral clock (꽃시계)
• Plants, being rooted to the ground, must
respond to environmental changes that come
their way
– For example, the bending of a seedling toward
light begins with sensing the direction, quantity,
and color of the light
© 2011 Pearson Education, Inc.
Figure 39.1
Concept 39.1: Signal transduction pathways
link signal reception to response
• A potato left growing in darkness produces
shoots that look unhealthy, and it lacks
elongated roots
• These are morphological adaptations for
growing in darkness, collectively called
etiolation(황화현상: 엽록소 형성없이 카로티노이드의 황색이 나타냄)
• After exposure to light, a potato undergoes
changes called de-etiolation(greening), in
which shoots and roots grow normally
© 2011 Pearson Education, Inc.
Figure 39.2
Dark condition
(a) Before exposure to light
Light condition
(b) After a week’s exposure
to natural daylight
What happen to potato?
• A potato’s response to light is an example of
cell-signal processing
• The stages are reception, transduction, and
response
© 2011 Pearson Education, Inc.
Figure 39.3
Review of a general model for signal transduction pathways
CELL
WALL
1 Reception
CYTOPLASM
2 Transduction
3 Response
Relay proteins and
second messengers
Receptor
Hormone or
environmental
stimulus
Plasma membrane
Activation
of cellular
responses
Reception
• Internal and external signals are detected by
receptors, proteins that change in response to
specific stimuli
• In de-etiolation, the receptor is a phytochrome
capable of detecting light
© 2011 Pearson Education, Inc.
Transduction
• Second messengers transfer and amplify
signals from receptors to proteins that cause
responses
• Two types of second messengers play an
important role in de-etiolation: Ca2+ ions and
cyclic GMP (cGMP)
• The phytochrome receptor responds to light by
– Opening Ca2+ channels, which increases Ca2+
levels in the cytosol
– Activating an enzyme that produces cGMP
© 2011 Pearson Education, Inc.
Figure 39.4-1
An example of signal transduction in plants: the role of
phytochrome in the de-etiolation response
1 Reception
CYTOPLASM
Plasma
membrane
Phytochrome
Cell
wall
Light
Figure 39.4-2
2 Transduction
1 Reception
CYTOPLASM
Plasma
membrane
cGMP
Second
messenger
Phytochrome
Protein
kinase 1
Cell
wall
Protein
kinase 2
Light
Ca2+ channel
Ca2+
Figure 39.4-3
2 Transduction
1 Reception
3 Response
Transcription
factor 1 NUCLEUS
CYTOPLASM
Plasma
membrane
cGMP
Second
messenger
Phytochrome
P
Protein
kinase 1
Transcription
factor 2
P
Cell
wall
Protein
kinase 2
Transcription
Light
Translation
Ca2+ channel
Ca2+
De-etiolation
(greening)
response proteins
Response
• A signal transduction pathway leads to
regulation of one or more cellular activities
• In most cases, these responses to stimulation
involve increased activity of enzymes
• This can occur by transcriptional regulation
or post-translational modification
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Post-Translational Modification of
Preexisting Proteins
• Post-translational modification involves
modification of existing proteins in the signal
response
• Modification often involves the phosphorylation
of specific amino acids
• The second messengers cGMP and Ca2+
activate protein kinases directly
© 2011 Pearson Education, Inc.
Transcriptional Regulation
• Specific transcription factors bind directly to
specific regions of DNA and control
transcription of genes
• Some transcription factors are activators that
increase the transcription of specific genes
• Other transcription factors are repressors that
decrease the transcription of specific genes
© 2011 Pearson Education, Inc.
De-Etiolation (“Greening”) Proteins
• De-etiolation activates enzymes that
– Function in photosynthesis directly
– Supply the chemical precursors for chlorophyll
production
– Affect the levels of plant hormones that regulate
growth
© 2011 Pearson Education, Inc.
Concept 39.2: Plant hormones help
coordinate growth, development, and
responses to stimuli
• Plant hormones are chemical signals that
modify or control one or more specific
physiological processes within a plant
© 2011 Pearson Education, Inc.
The Discovery of Plant Hormones
• Any response resulting in curvature of organs
toward or away from a stimulus is called a
tropism(굴성)
• In the late 1800s, Charles Darwin and his son
Francis conducted experiments on
phototropism(굴광성), a plant’s response to light
• They observed that a grass seedling could bend
toward light only if the tip of the coleoptile(자엽초, 떡잎)
was present
• They postulated that a signal was transmitted
from the tip to the elongating region (see next
slide)
© 2011 Pearson Education, Inc.
Figure 39.5
What part of a grass coleoptile senses light, and
how is the signal transmitted?
RESULTS
Shaded
side
Control
(1) 정단부위에서만 빛 인지함
(2) 굴광성을 유도하는 신호는 빛에 의해
활성화되어 이동 가능한 화학물질임
Light
Boysen-Jensen(1913년)
Illuminated
side
Light
Phototropism occurs only when the tip is illuminated
 The tip senses light
Darwin and Darwin (1880년)
Light
Gelatin
(permeable)
Tip
removed
Opaque
cap
Transparent
cap
Opaque
shield over
curvature
Mica(운모)
(impermeable)
Phototropism occurs when the tip is
separated by a permeable barrier but not an
impermeable barrier
The signal was a mobile chemical substance
• In 1926, Frits Went extracted the chemical
messenger for phototropism, auxin, by modifying
earlier experiments
Figure 39.6
RESULTS
Excised tip on
agar cube
Does asymmetrical distribution
of a growth-promoting
chemical cause a coleoptile to
grow toward the light?
Growth-promoting
chemical diffuses
into agar cube
Control
(agar cube
lacking
chemical)
Control has no effect
자엽초의 굴광성은
어두운 부분은 고농도의
옥신이 분포해서
발생하는 것임
© 2011 Pearson Education, Inc.
Agar cube with
chemical stimulates
growth
Offset cubes
cause curvature
화학물질을
균일하게 전달되는
경우 직선성장
경사지게 놓아 둔
조각은 식물을
휘어지게 함
A Survey of Plant Hormones
• Plant hormones are produced in very low
concentration, but a minute amount can greatly
affect growth and development of a plant organ
• In general, hormones control plant growth and
development by affecting the division, elongation,
and differentiation of cells
© 2011 Pearson Education, Inc.
Table 39.1
종자의 배, 줄기
정단분열조직,
어린잎
뿌리에서 합성되어
다른 기관으로 이동
줄기정단분열조직,
뿌리분열조직, 어린잎, 배
성장촉진, 발아촉진, 노화지연
종자, 눈의 발아, 줄기신장, 잎생장 촉진,
뿌리생장과 분화 조절
뿌리생장 억제, 잎의 탈리 지연, 물관형성 촉진
생장억제, 종자휴면 유도, 기공 폐쇄
과일성숙 촉진
Auxin
• The term auxin refers to any chemical that
promotes elongation of coleoptiles
• Indoleacetic acid (IAA) is a common auxin in
plants; in this lecture the term auxin refers
specifically to IAA
• Auxin is produced in shoot tips and is
transported down the stem
• Auxin transporter proteins move the hormone
from the basal end of one cell into the apical end
of the neighboring cell
© 2011 Pearson Education, Inc.
Figure 39.7
•
Q: What causes polar movement of
auxin from shoot tip to base?
Auxin transporters (옥신 수송체는 한
세포의 기저부에 위치하여 극성수송을
가능하게 함)
– Move the hormone out of the basal
end of one cell, and into the apical
end of neighboring cells
100 µm
RESULTS
Cell 1
Cell 2
Epidermis
Cortex
Conclusion: The results
Phloem
support the hypothesis that
concentration of the auxin Xylem
transport protein at the
basal ends of cells
Pith
mediates the polar transport
of auxin
25 µm
Basal end
of cell
옥신 수송단백질의
항체를 녹색형광물질로
표지한 후 위치추적함
The Role of Auxin in Cell Elongation
• According to the acid growth hypothesis, auxin
stimulates proton pumps in the plasma
membrane
• The proton pumps lower the pH in the cell wall,
activating expansins, enzymes that loosen the
wall’s fabric
• With the cellulose loosened, the cell can
elongate
© 2011 Pearson Education, Inc.
Figure 39.8
Cell elongation in response to auxin:
the acid growth hypothesis
Cross-linking
polysaccharides
Cell wall–loosening
enzymes
(3) Wedge-shaped expansins, activated by low pH, separate cellulose
microfibrils from cross-linking polysaccharides. The exposed cross-linking
polysaccharides are now more accessible to cell wall enzymes.
Expansin
CELL WALL
Cellulose
microfibril
(4) The enzymatic cleaving
of the cross-linking
polysaccharides allows
the microfibrils to slide.
The extensibility of the
cell wall is increased. Turgor
causes the cell to expand.
H2O
H+
(2) The cell wall
becomes more
acidic.
H+
H+
(1) Auxin
increases the
activity of
proton pumps.
Plasma
membrane
H+
ATP
H+
H+
H+
Cell wall
H+
H+
Plasma membrane
CYTOPLASM
Nucleus Cytoplasm
Vacuole
(5) With the cellulose loosened,
the cell can elongate.
• Auxin also alters gene expression and
stimulates a sustained growth response
© 2011 Pearson Education, Inc.
Auxin’s Role in Plant Development
• Polar transport of auxin plays a role in pattern
formation of the developing plant
• Auxin is synthesized in shoot tips
• Reduced auxin flow from the shoot of a branch
stimulates growth in lower branches
• Auxin transport plays a role in phyllotaxy(잎차례), the
arrangement of leaves on the stem(줄기에 잎이 달리는 배열상태)
• Polar transport of auxin from leaf margins(잎둘레)
directs the patterns of leaf veins (극성옥신수송을 저해하면 잎자루의
관다발 연속성이 결핍한 잎사귀 초래)
• The activity of the vascular cambium is under
control of auxin transport (식물체가 휴면기에 들어갈때 옥신수송능력
감소와 옥신수송체의 유전자발현의 감소와 관련됨)
© 2011 Pearson Education, Inc.
Practical Uses for Auxins
• The auxin indolbutyric acid (IBA) stimulates
adventitious roots and is used in vegetative
propagation of plants by cuttings : treating a
detached leaf or stem with powder containing IBA
causes adventitious roots to form near the cut
surface
• An overdose of synthetic auxins can kill plants
– For example 2,4-D is used as an herbicide on
eudicots (Monocots such as maize and turfgrass can rapidly
inactivate such synthetic auxins  2,4-D spray를 이용하면 쌍떡잎
씨앗을 제거할 수 있음)
© 2011 Pearson Education, Inc.
Cytokinins
• Cytokinins are so named because they
stimulate cytokinesis (cell division)
•
•
•
•
1940s Johannes van Overbeek에 의해 발견
코코넛 밀크를 첨가하면 식물성장 촉진
핵산인 아데닌의 변형물질임이 밝혀짐 (Skoog & Miller)
대표적인 시토키닌은 옥수수에서 발견된 zeatin임
© 2011 Pearson Education, Inc.
(1) Control of Cell Division and Differentiation
• Cytokinins are produced in actively growing tissues
such as roots, embryos, and fruits
• Cytokinins work together with auxin to control
cell division and differentiation
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(2) Control of Apical Dominance (정단우성조절)
• Cytokinins, auxin, and strigolactone interact in
the control of apical dominance, a terminal bud’s
ability to suppress development of axillary buds
• If the terminal bud is removed, plants become
bushier (숱이 많아짐)
© 2011 Pearson Education, Inc.
Figure 39.9a
(1) 끝눈의 옥신이 곁눈의
생장을 억제하며 줄기의
주축성장을 촉진함
(2) 뿌리에서 이동되어 온
시토키닌은 옥신과는
반대로 곁눈생장을 촉진함
Axillary buds
(a) Apical bud intact (not shown in photo)
Figure 39.9b
끝눈의 제거시
옥신의 주요생성장소인
끝눈이 없으므로 상대적으로
시토키닌의 기능이 우세하게
되어 곁눈생장을 촉진되며
따라서 곁가지가 자람
Lateral branches
“Stump (잘리고
난 남은 부분)” after
removal of
apical bud
(b) Apical bud removed
Figure 39.9c
끝눈의 제거후 옥신 첨가시
곁눈의 성장 억제
(c) Auxin added to decapitated stem
(3) Anti-Aging Effects
• Cytokinins slow the aging of some plant organs by
inhibiting protein breakdown, stimulating RNA and
protein synthesis, and mobilizing nutrients from
surrounding tissues
• Cytokinins slow the progress of apoptosis
• 시토키닌 용액에 잎을 담가두면 오랫동안 싱싱한 상태를
유지할 수 있다
• 화초재배자들은 시토키닌 스프레이를 꽃의 신선도 유지를
위해 사용함
© 2011 Pearson Education, Inc.
Gibberellins
• 1926년, 일본 식물병리학자인 Kurosawa에 의해
발견
• 키만 멀대처럼 큰 허약한 벼의 원인균인
Gibberella속의 곰팡이에서 특정 화학물질이
분비되어 벼 줄기의 길이신장을 유도함을 알게
되었고 이를 지베렐린으로 명명함
• Gibberellins have a variety of effects, such
as stem elongation, fruit growth, and
seed germination
© 2011 Pearson Education, Inc.
Stem Elongation
• Gibberellins are produced in young roots and
leaves
• Gibberellins stimulate growth of leaves and
stems
• In stems, they stimulate cell elongation and cell
division: 세포벽을 느슨하게 해 주는 효소의 활성화를 유도하여
expansin의 세포벽 안쪽으로의 유입을 촉진하여 세포신장 발생함
• Bolting(추대): 꽃자루의 급격한 생장현상; 배추는
영양생장기에는 로제트형태(키가 낮고 땅에 붙은)로 자라고,
생식생장기에는 지베렐린의 농도증가로 인해 줄기 마디사이의
급격한 신장으로 꽃눈의 위치가 위로 올라감
© 2011 Pearson Education, Inc.
Figure 39.10a
(a) Rosette form (left) and
gibberellin-induced bolting (추대:
(right)
꽃줄기 형성)
Fruit Growth
• In many plants, both auxin and gibberellins must
be present for fruit to develop
• Gibberellins are used in spraying of Thompson
seedless grapes
Figure 39.10b
(b) Grapes from control vine
(left) and gibberellin-treated
vine (right)
© 2011 Pearson Education, Inc.
Germination
• After water is imbibed(absorbed), release of
gibberellins from the embryo signals seeds to
break dormancy and germinate
© 2011 Pearson Education, Inc.
Figure 39.11
Mobilization of nutrients by GA during the
germination of grain seeds such as barley
Aleurone(호분층)
Endosperm 1
2
3
(배젖)
α-amylase
Sugar
GA
Water
GA
Scutellum
(cotyledon)
Radicle
(어린뿌리, 유근)
(떡잎)
 종자에 물이 흡수되면
배로부터 GA방출되어
호분층에 신호전달
 호분층에서는 소화효소
(알파 아밀라제) 분비하여
배젖의 영양분을
가수분해함
떡잎에 의해
배젖으로부터 흡수된
영양분은 배발생동안
소비됨
Brassinosteroids
• Brassinosteroids are chemically similar to the
sex hormones of animals
• They induce cell elongation and division in stem
segments and seedlings
• They slow leaf abscission(leaf drop, 낙옆) and promote
xylem differentiation
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Abscisic Acid(앱시스산)
• Abscisic acid (ABA) slows growth
• ABA often antagonizes the actions of growth
hormones, and the ratio of ABA to one or more
growth hormones determines the final physiological
outcome
• Two of the many effects of ABA
– Seed dormancy(종자 휴면)
– Drought tolerance(내건성)
© 2011 Pearson Education, Inc.
Seed Dormancy
• Seed dormancy ensures that the seed will
germinate only in optimal conditions
• In some seeds, dormancy is broken when ABA
is removed by heavy rain, light, or prolonged
cold
• Precocious (early) germination can be
caused by inactive or low levels of ABA
• ABA와 GA간의 농도비가 휴면 또는 발아의
결정에 중요함 (see next slide)
© 2011 Pearson Education, Inc.
Figure 39.12a
Red mangrove
(Rhizophora mangle)
seeds
• Precocious germination is observed in maize mutants That
lack a functional transcription factor required for ABA to
induce expression of certain genes (앱시스산에 의해 조절되는
전사조절인자의 돌연변이로 인해 휴면관련 유전자발현에 이상이 생김)
Coleoptile
Figure 39.12b
Maize mutant
Drought Tolerance
• ABA is the primary internal signal that enables
plants to withstand drought
• ABA accumulation causes stomata to close
rapidly
© 2011 Pearson Education, Inc.
Strigolactones
• The hormones called strigolactones
– Stimulate seed germination
– Help establish mycorrhizal associations (균근공생)
– Help control apical dominance
• Strigolactones are named for parasitic Striga
plants (악마의 풀)
• Striga seeds germinate when host plants
exude strigolactones through their roots
© 2011 Pearson Education, Inc.
Ethylene
• A gaseous plant hormone
• Plants produce ethylene in response to stresses
such as drought, flooding, mechanical pressure,
injury, and infection
• The effects of ethylene include response to
mechanical stress, senescence, leaf
abscission, and fruit ripening
© 2011 Pearson Education, Inc.
(1) The Triple Response to Mechanical Stress
• Ethylene induces the triple response, which
allows a growing shoot to avoid obstacles
• The triple response consists of a slowing of
stem elongation, a thickening of the stem, and
horizontal growth
© 2011 Pearson Education, Inc.
Figure 39.13
0.00
0.10
0.20
0.40
0.80
Ethylene concentration (parts per million)
• Ethylene-insensitive mutants fail to undergo the
triple response after exposure to ethylene
• Other mutants undergo the triple response in air
but do not respond to inhibitors of ethylene
synthesis
© 2011 Pearson Education, Inc.
Figure 39.14a
ein mutant
Ethylene-insensitive mutants
(ein mutant):
Fail to undergo the triple
response after exposure to
ethylene
(a) ein mutant
Figure 39.14b
ctr mutant
Other types of mutants (ctr mutant):
Undergo the triple response in air but
do not respond to inhibitors of
ethylene synthesis (에틸렌 신호전달
과정이 지속적인 가동으로 인해 항상
3중반응을 보이며, 에틸렌 합성 저해제
처리에도 3중반응 보임)
ctr돌연변이 유전자는 protein kinase을
암호화하며, 이 효소는 에틸렌 신호전달과정의
negative regulator로 추정됨
(b) ctr mutant
(2) Senescence
• Senescence is the programmed death of cells
or organs
• A burst of ethylene is associated with
apoptosis, the programmed destruction of cells,
organs, or whole plants
(3) Leaf Abscission
• A change in the balance of auxin and ethylene
controls leaf abscission, the process that
occurs in autumn when a leaf falls
© 2011 Pearson Education, Inc.
Figure 39.15
옥신과 에틸렌의 상대적인 농도변화에
따른 잎의 탈리 조절반응
0.5 mm
오랜된 잎에서는 옥신의 합성
감소로 탈리층 세포의 에틸렌에
대한 민감성 증가 초래
에틸렌의 효과 증대로 세포들은
셀룰로오스 등의 세포벽
구성물질을 분해하는 효소의
합성을 촉진하여 탈리를 유도함
Protective layer
Abscission layer
Stem
Petiole
단풍나무
잎의 탈리
(4) Fruit Ripening
• A burst of ethylene production in a fruit triggers
the ripening process
• Ethylene triggers ripening, and ripening triggers
release of more ethylene
• Fruit producers can control ripening by picking
green fruit and controlling ethylene levels
© 2011 Pearson Education, Inc.
Concept 39.3: Responses to light are critical
for plant success
• Light cues many key events in plant growth and
development
• Effects of light on plant morphology are called
photomorphogenesis(광형태형성)
© 2011 Pearson Education, Inc.
• Plants detect not only presence of light but also
its direction, intensity, and wavelength (color)
• A graph called an action spectrum(작용스펙트럼)
depicts relative response of a process to
different wavelengths
• Action spectra are useful in studying any
process that depends on light
– 식물체에서 두 종류의 빛수용체가 있음
– 광형태형성과정(photomorphogenesis)에는 적색광과
청색광이 가장 중요함
– 청색광은 blue-light photoreceptor, 적색광은
phytochrome(피토크롬)에 의해 흡수됨
© 2011 Pearson Education, Inc.
Figure 39.16
Phototropic effectiveness
What wavelengths
stimulate phototropic
bending toward light?
(어떤 파장의 빛이 굴광성을
유도하나?)
1.0
0.8
0.6
0.4
0.2
0
굴광성은 청색과 보라색
빛에 민감한 광수용체에
의해 발생함
436 nm
400
450
500
550
600
650
700
Wavelength (nm)
(a) Phototropism action spectrum
Light
Time = 0 min
Time = 90 min
(b) Coleoptiles before and after light exposures
Blue-light photoreceptors와
phytochromes의 발견
• Research on action spectra and absorption
spectra of pigments
– Led to the identification of two major classes of light receptors:
blue-light photoreceptors and phytochromes
(1) Blue-Light Photoreceptors
•
Various blue-light photoreceptors
–
Control hypocotyl elongation, stomatal opening, and phototropism
(자엽하축 신장, 기공열림, 굴광성의 조절)
(2) Phytochromes as Photoreceptors
•
Phytochromes
–
Regulate many of a plant’s responses to light throughout its life
–
종자발아(seed germination), 음지회피반응(shade avoidance)
© 2011 Pearson Education, Inc.
Phytochromes and Seed Germination
• Many seeds remain dormant until light conditions
change
• In the 1930s, scientists at the U.S. Department of
Agriculture determined the action spectrum for
light-induced germination of lettuce seeds
© 2011 Pearson Education, Inc.
Figure 39.17
How does the order of red and far-red illumination affect seed
germination? (적색광과 원적외선의 조사순서가 종자발아 미치는 영향은?)
RESULTS
미발아
발아
Red
Dark
Red Far-red
Dark
미발아
발아
Dark (control)
Red Far-red Red
Dark
Red Far-red Red Far-red
(1) 적색광은 발아촉진, 원적외선은 발아억제함
(2) 최종조사한 빛의 종류가 결정인자임
(3) 적색광과 원적외선의 효과는 가역적임
• The photoreceptor responsible for the opposing
effects of red and far-red light is a phytochrome
Figure 39.18 :
Structure of phytochrome
Two identical subunits
(1) 피토크롬은 두개의
동일한 단백질이
결합되어 기능을 나타냄
(2) 광수용체 활성부위는
비단백질성 색소인
색소포와 공유결합을 함
(3) 인산화 활성부위는
빛수용반응과 세포내
신호전달과정을
연결하는 기능
© 2011 Pearson Education, Inc.
Chromophore
(색소포: nonprotein pigment)
Photoreceptor activity
Kinase activity
Figure 39.UN01
The chromophore of phytochrome is photoreversible
Red light
Pr
Pfr
Far-red light
Phytochrome: a molecular switching mechanism
• Phytochromes exist in two photoreversible
states, with conversion of Pr to Pfr triggering
many developmental responses
• Red light triggers the conversion of Pr to Pfr
• Far-red light triggers the conversion of Pfr to Pr
• The conversion to Pfr is faster than the
conversion to Pr
• Sunlight increases the ratio of Pfr to Pr, and
triggers germination (see next slide)
© 2011 Pearson Education, Inc.
Figure 39.19
Sunlight
Pr
Pfr
Red light
Synthesis
Responses:
seed
germination,
control of
flowering, etc.
Far-red
light
Slow conversion
in darkness
(some plants)
Enzymatic
destruction
Phytochromes and Shade Avoidance
• The phytochrome system also provides the plant with
information about the quality of light
• Leaves in the canopy(차양막) absorb red light
• Shaded plants receive more far-red than red light
• In the “shade avoidance” response, the phytochrome
ratio shifts in favor of Pr when a tree is shaded
나무가 직접 햇빛을 받으면 Pfr의 농도가 증가하여 수직성장은
억제되고 곁가지의 생장이 촉진되어 옆으로 퍼지게 됨
키 큰 나무에 의해 음지에 놓이게 되면 잎을 통과한 원적외선을
조사받게 되므로 Pr의 농도가 증가하여 수직성장이 촉진됨 
햇빛을 많이 받게 위한 전략임
© 2011 Pearson Education, Inc.
Biological Clocks and Circadian Rhythms
• Many plant processes oscillate during the day
• 일정 환경조건 속에서도 기공개폐, 광합성관련 효소의 합성 등 식물체 내의
많은 생리작용은 24시간의 주기에 따라 조절됨
• Many legumes(콩과식물) lower their leaves in the
evening and raise them in the morning, even
when kept under constant light or dark
conditions (see next slide)
© 2011 Pearson Education, Inc.
Figure 39.20
Sleep movements of a bean plant
Noon
Midnight
The movements are caused by reversible changes in the tugor pressure of
cells on opposing sides of the pulvini(옆침), motor organs of the leaf
• Circadian rhythms are cycles that are about
24 hours long and are governed by an internal
“clock”
• Circadian rhythms can be entrained to exactly
24 hours by the day/night cycle
• The clock may depend on synthesis of a
protein regulated through feedback control and
may be common to all eukaryotes
© 2011 Pearson Education, Inc.
The Effect of Light on the Biological Clock
• Phytochrome conversion marks sunrise and
sunset, providing the biological clock with
environmental cues
어두운 곳: 피토크롬의 비율은 Pr이 높아짐. 즉, Pr형태로
합성되며 Pfr이 Pr보다 쉽게 분해됨
빛이 있으면 Pr은 Pfr로 재빨리 전환되어 생체시계를 다시 맞추어 줌
© 2011 Pearson Education, Inc.
Photoperiodism(광주기성) and Responses to Seasons
• Photoperiod, the relative lengths of night and
day, is the environmental stimulus plants use
most often to detect the time of year
• Photoperiodism is a physiological response to
photoperiod
© 2011 Pearson Education, Inc.
Photoperiodism and Control of Flowering(개화)
• Some processes, including flowering in many
species, require a certain photoperiod
• Plants that flower when a light period is shorter
than a critical length are called short-day plants
• Plants that flower when a light period is longer
than a certain number of hours are called longday plants
• Flowering in day-neutral plants is controlled by
plant maturity, not photoperiod
© 2011 Pearson Education, Inc.
– 단일식물(short-day plants): 낮의 길이가 개화에
필요한 특정길이보다 짧으면 개화하는 식물 (늦여름,
가을, 겨울에 개화.); 국화(chrysanthemums),
포인세티아스, 콩과 식물(soybean)
– 장일식물(long-day plants): 광주기가 특정
시간보다 길어야 개화함 (늦봄이나 초여름에 개화.
즉, 낮이 14시간 이상일 때); 시금치, 무우, 상치, 붓꽃
(iris), 곡물류
– 중일식물(Day-neutral plants): 개화가 광주기와
상관없는 식물로서 maturity에 따라 개화; 민들레
토마토, 벼
Critical Night Length
• In the 1940s, researchers discovered that
flowering and other responses to
photoperiod are actually controlled by night
length, not day length
© 2011 Pearson Education, Inc.
How to control flowering by photoperiodic system
• Short-day plants are governed by whether the
critical night length sets a minimum number of
hours of darkness
• Long-day plants are governed by whether the
critical night length sets a maximum number of
hours of darkness
© 2011 Pearson Education, Inc.
Figure 39.21
24 hours
How does interrupting the dark
peroid with a brief exposure to
light affect flowering?
(암기 중 빛의 조사가 개화에
미치는 영향은?)
(a) Short day
(long-night) plant
Light
각 식물 종의 개화는
밤길이에 의해 결정됨.
따라서 short-day plant는
long-night plant로, longday plant는 short-night
plant로 부르는 게 타당함
Flowers when night
exceeds a critical dark
period. A flash of light
interrupting the dark
period prevents
Flash Darkness flowering
of
Critical
dark period light
(b) Long-day
(short-night) plant
Flowers only if the night
is shorter than a critical
dark period. A brief flash
of light interrupts a long
dark period, thereby
inducing flowering
Flash
of light
Reversible effect of red and far-red light on
photoperiodic response
• Red light can interrupt the nighttime portion of
the photoperiod
• A flash of red light followed by a flash of far-red
light does not disrupt night length
• Action spectra and photoreversibility
experiments show that phytochrome is the
pigment that receives red light (see next slide)
© 2011 Pearson Education, Inc.
Figure 39.22
24 hours
Is phytochrome the
pigment that measures the
interruption of dark
peroids in photoperiodic
response? (피토크롬이
광주기 반응에서 암기의
중단을 인지하는 색소인가?)
R
(1) 적색광 조사는 암기를 짧게
하며, 근적외선의 연이은
조사는 적색광이 효과를
반전시킴. 그 역반응도
가능함
(2) 이런 가역성은 피토크롬이
dark period의 중단을
인식하는 색소임을 입증함
R FR
RFR R
R FRR FR
Critical dark period
Long-day
Short-day
(long-night) (short-night)
plant
plant
• Some plants flower after only a single exposure
to the required photoperiod
• Other plants need several successive days of
the required photoperiod
• Still others need an environmental stimulus
in addition to the required photoperiod
– For example, vernalization(춘화처리) is a
pretreatment with cold to induce flowering
© 2011 Pearson Education, Inc.
A Flowering Hormone?
• Photoperiod is detected by leaves, which cue
buds to develop as flowers
• The flowering signal is called florigen
• Florigen may be a macromolecule governed
by the FLOWERING LOCUS T (FT) gene
© 2011 Pearson Education, Inc.
Figure 39.23
Experimental evidence for a flowering hormone
24 hours
24 hours
Long-day plant
grafted to
short-day plant
Long-day
plant
24 hours
Graft
Short-day
plant
Under short-day conditions, a short-day plant will flower and a long-day one
will not. However, both flower if grafted together and exposed to short days
Concept 39.4: Plants respond to a wide
variety of stimuli other than light
• Because of immobility, plants must adjust to a
range of environmental circumstances through
developmental and physiological mechanisms
(1) Gravity
(2) Mechanical Stimuli
(3) Environmental stresses
Drought
Flooding
Salt Stress
Heat Stress
Cold stress
© 2011 Pearson Education, Inc.
Gravity
• Response to gravity is known as
gravitropism(굴중성)
• Roots show positive gravitropism; shoots
show negative gravitropism
• Plants may detect gravity by the settling of
statoliths, dense cytoplasmic components
Statoliths [stǽtəlìθ] : 평형립, specialized
plastids containing dense starch grains
© 2011 Pearson Education, Inc.
Figure 39.24
Positive gravitropism in roots:
the statolith hypothesis
뿌리가 수평으로 놓인 후
수분내로 평형립은 골무세포의
기저부로 모이게 됨
평형립 가설에 의하면 이렇게
평형립이 놓이게 되는 것이
중력감지기작이며 칼슘의
재분포를 유도하여 옥신의
측면수송을 가능게 함으로써
뿌리 아래쪽은 옥신의 농도가
높아져 세포신장이 억제되며,
따라서 뿌리 안팎의
세포신장률을 다르게 되고
뿌리가 굽어지게 되는 것임
Statoliths
(a) Primary root of maize
bending gravitropically
(LMs)
20 µm
(b) Statoliths settling to
the lowest sides of
root cap cells (LMs)
• Some mutants that lack statoliths are still
capable of gravitropism
• Dense organelles, in addition to starch granules,
may contribute to gravity detection
© 2011 Pearson Education, Inc.
Mechanical Stimuli
• The term thigmomorphogenesis(접촉형태형성) refers
to changes in form that result from mechanical
disturbance (thigma=touch)
• Rubbing stems of young plants a couple of
times daily results in plants that are shorter
than controls (see next slide)
© 2011 Pearson Education, Inc.
Figure 39.25
Altering gene expression by touch in
Arabidopsis
기계적인 자극으로 세포내
칼슘농도 변화가 유도되고
세포벽의 성질을 변화시킬
수 있는 유전자발현을
촉진하게 됨
• Thigmotropism(굴촉성) is growth in response to
touch
• It occurs in vines and other climbing plants
•
포도나무를 포함하는 덩굴식물들은 덩굴손을 가지고 있으며 접촉이 없으면
곧게 자라지만 접촉이 있으면 덩굴손 양쪽 세포의 생장 차이가 생겨
동그랗게 말리는 현상(coiling response)이 유도됨.
• Another example of a touch specialist is the
sensitive plant Mimosa pudica, which folds its
leaflets and collapses in response to touch
• Rapid leaf movements in response to
mechanical stimulation are examples of
transmission of electrical impulses called
action potentials
Ex: Rapid tugor movements by the sensitive
plant (see next slide)
© 2011 Pearson Education, Inc.
Figure 39.26
(a) Unstimulated state
(b) Stimulated state
Side of pulvinus
with flaccid cells
Pulvinus
(motor
organ)
(c) Cross section of a leaflet pair in the stimulated state (LM)
(흐늘흐늘해진 엽침의 측면)
Side of pulvinus
with turgid cells
(팽팽해진 엽침 측면)
Vein
0.5 µm
Leaflets
after
stimulation
미모사의 잎은 자극에 반응하여
소엽의 안쪽은 K+ 이온손실이
유도되고 이로인해 삼투압에 인한
물손실로 쭈글쭈글해지고 바깥쪽은
팽팽한 상태로 유지됨
 따라서 운동기관인 엽침의
굽어지는 현상이 유발됨
Environmental Stresses
• Environmental stresses have a potentially
adverse effect on survival, growth, and
reproduction
• Stresses can be abiotic (nonliving) or biotic
(living)
• Abiotic stresses include drought, flooding,
salt stress, heat stress, and cold stress
• Biotic stresses include herbivores and
pathogens
© 2011 Pearson Education, Inc.
Drought
• During drought, plants reduce transpiration by
closing stomata, slowing leaf growth, and
reducing exposed surface area
• Growth of shallow roots is inhibited, while
deeper roots continue to grow
© 2011 Pearson Education, Inc.
Flooding
• Enzymatic destruction of root cortex cells
creates air tubes that help plants survive
oxygen deprivation during flooding (홍수로 인한
산소부족을 극복하도록 예정된 세포죽음을 통해 공기통로를 생성함)
© 2011 Pearson Education, Inc.
Figure 39.27
A developmental response of maize roots
to flooding and oxygen deprivation
(홍수시의 옥수수뿌리의 발달 반응)
공기공급한 대조군 뿌리
공기공급 중단한 뿌리
Vascular
cylinder
Air tubes
Epidermis
100 µm
(a) Control root (aerated)
100 µm
(b) Experimental root (nonaerated)
Salt Stress
• Salt can lower the water potential of the soil
solution and reduce water uptake
• Plants respond to salt stress by producing
solutes tolerated at high concentrations
• This process keeps the water potential of cells
more negative than that of the soil solution
염류 농도가 높아지면 토양의 수분포텐셜이 감소하여 식물은 수분부족을 겪게 됨
유기물 용질을 합성하여 세포의 수분포텐셜을 토양의 그것보다 낮게
유지함으로써 해로운 염류의 유입을 방지함
© 2011 Pearson Education, Inc.
Heat Stress
• Excessive heat can denature a plant’s
enzymes
• Heat-shock proteins help protect other
proteins from heat stress
© 2011 Pearson Education, Inc.
Cold Stress
• Cold temperatures decrease membrane fluidity
• Altering lipid composition of membranes is a
response to cold stress
– 불포화지방산의 비중을 높여 저온에서 지질이 고형화되는 것을 방지  막의 유동성 유지
– 동결스트레스를 견디기 위해 겨울이 오기 전에 당분과 같은 특정 용질의 농도를 증가시켜
세포바깥이 얼더라도 수분손실을 최소화함
• Freezing causes ice to form in a plant’s cell walls
and intercellular spaces
• Many plants, as well as other organisms, have
antifreeze proteins that prevent ice crystals
from growing and damaging cells
© 2011 Pearson Education, Inc.
Concept 39.5: Plants respond to attacks by
herbivores and pathogens (Biotic stresses)
• Plants use defense systems to deter herbivory,
prevent infection, and combat pathogens
© 2011 Pearson Education, Inc.
Defenses Against Herbivores
• Herbivory, animals eating plants, is a stress that
plants face in any ecosystem
• Plants counter excessive herbivory with
physical defenses, such as thorns and
trichomes, and chemical defenses, such as
distasteful or toxic compounds
•
특정 식물에 의한 Canavanine 생성 (아르기닌 유사아미노산)  곤충섭취시 canavanine은
곤충의 단백질 속으로 들어가게 되고 단백질 구조 또는 기능 이상을 유도하여 곤충을 죽게 함
• Some plants even “recruit” predatory animals
that help defend against specific herbivores (see
next slide)
© 2011 Pearson Education, Inc.
Figure 39.28
A maize leaf “recruiting” a parasitoid wasp as a
defensive response to an armyworm caterpillar, an
herbivore (초식동물의 포식자 유인용 휘발성물질 방출)
4 Recruitment of
parasitoid wasps
that lay their eggs
within caterpillars
1 Wounding
1 Chemical
in saliva
2 Signal transduction
pathway
3 Synthesis
and release
of volatile
attractants
Defenses Against Pathogens
• A plant’s first line of defense against infection is
the barrier presented by the epidermis and
periderm
• If a pathogen penetrates the dermal tissue, the
second line of defense is a chemical attack
that kills the pathogen and prevents its
spread
• This second defense system is enhanced by the
inherited ability to recognize certain pathogens
© 2011 Pearson Education, Inc.
Host-Pathogen Coevolution
• A virulent pathogen is one that a plant has little
specific defense against
• An avirulent pathogen is one that may harm but
does not kill the host plant
© 2011 Pearson Education, Inc.
• Gene-for-gene recognition involves
recognition of elicitor molecules by the protein
products of specific plant disease resistance (R)
genes
• An R protein recognizes a corresponding
molecule made by the pathogen’s Avr gene
• R proteins activate plant defenses by triggering
signal transduction pathways
• These defenses include the hypersensitive
response and systemic acquired resistance
© 2011 Pearson Education, Inc.
The Hypersensitive Response
• The hypersensitive response
– Causes cell and tissue death near the infection
site
– Induces production of phytoalexins and PR
(pathogenesis-related proteins) proteins, which
attack the pathogen
– Stimulates changes in the cell wall that confine
the pathogen
© 2011 Pearson Education, Inc.
Defense responses against an avirulent
pathogen (fig. 39.29)
(1) Specific resistance is based on the binding of pathogen effector
molecules to specific plant resistance R proteins
(2) The identification in step 1 triggers a signal transduction pathway
(3) In a hypersensitive response, plant cells produce antimicrobial
molecules, seal off infected areas by modifying their walls, and then
destroy themselves. This localized response produces lesions and
protects other parts of an infected leaf
(4) Before they die, infected cells release the signaling molecule
methylsalicylic acid
(5) The signaling molecule is distributed to the rest of the plant
(6) In cells remote from the infection site, methylsalicylic acid is converted
to salicylic acid, which initiates a signal transduction pathway
(7)Systemic acquired resistance is activated: the production of molecules
that help protect the cell against a diversity of pathogens for several
days
Figure 39.29
Infected tobacco leaf with lesions
4
3
Signal
5
Hypersensitive
response
Signal
transduction
pathway
6
2 Signal transduction pathway
7
Acquired
resistance
1
R protein
Avirulent
pathogen
Avr effector protein
R-Avr recognition and
hypersensitive response
Systemic acquired
resistance
Systemic Acquired Resistance
• Systemic acquired resistance causes
systemic expression of defense genes and is
a long-lasting response
• Salicylic acid is synthesized around the
infection site and is likely the signal that
triggers systemic acquired resistance
© 2011 Pearson Education, Inc.