This document discusses plant movements, which are divided into movements of locomotion and movements of curvature. Movements of locomotion involve the whole plant or parts moving from one place to another, and include autonomous movements like cytoplasmic streaming as well as induced movements in response to stimuli. Movements of curvature involve bending or coiling of plant parts without changing position, and can be autonomous due to growth differences or induced by external stimuli. Induced movements include tropisms like phototropism in response to light, as well as nastic movements whose direction is determined by the plant and not the stimulus, such as opening and closing of leaves and flowers.

1. CONTROL AND
COORDINATION IN PLANTS
T V Preethi

2. Introduction

4. PLANT MOVEMENTS ARE MAINLY DIVIDED IN TWO PARTS
1.Movements of Locomotion
2.Movements of Curvature
1. Movements of Locomotion –
In this type of movement Plant’s whole body or a part of plant goes from one
place to another. In short plant changes its position, is called movements of
locomotion.
Those movements in which whole of the plant body or the cell or cytoplasm
moves from one place to another are called as movements of locomotion. These
movements may occur either spontaneously or in response to a certain external
stimulus and are called as autonomic and paratonic (or induced) movements
respectively. Paratonic movements of locomotion are also known as tactic
movements.
This type of movements is also divided in two types –

5. Movements of Locomotion
I. Autonomous Movements – This type of movements is induced by internal
stimuli. It is divided in 3 parts –
A. Amoeboid - e.g. Gametes of Spirogyra
B. Ciliary -
Such type of movements take place due to the presence of cilia or flagella e.g.,
Chlamydomonas, Volvox, flagellated or ciliated reproductive cells etc.
C. Cyclosis –
In living cells of many plants the cytoplasm including various cell-organelles
moves around the vacuoles. This movement of the cytoplasm is called
protoplasmic streaming or cyclosis. It is of two types—rotation and circulation. In
rotation, which is exhibited by plants like Chara, Hydrilla Vallisneria, Elodea etc.,
the cytoplasm moves either clockwise or anti-clockwise around a larger central
vacuole. While in circulation, which is exhibited by the cell of staminal hairs of
plants like Tradeschantia, the cytoplasm moves in both clockwise and
anticlockwise directions around many smaller vacuoles
a. Rotation – When protoplasm moves around the central vacuole.
e.g. Hydrilla, Vallisneria
b. Circulation – When protoplasm moves randomly in cell.
e.g. Tradescantia
Cytoplasmic Streaming in
Tradescantia Stamen Hair
Cells
https://www.youtube.com/watc
h?v=AgFpsVS3xXg
Rotation
Gametes of Chlamydomonas
Gametes of Spirogyra

6. II. Induced or Para tonic Movements – It is induced by External stimuli. It is
also divided in 3 types
A. Chemo-tactic
These movements occur in response to an external chemical stimulus. Such
movements are exhibited most commonly by the antherozoids in bryophytes and
pteridophytes where the archegonia secrete some chemical substances having a
peculiar odour towards which the antherozoids are attracted chemotactically.
e.g. Anthaloziades
B. Photo-tactic
These movements occur in response to an external stimulus, the light and are
exhibited by zoospores and gametes of certain algae e.g., Chlamydomonas,
Volvox, Ulothrix, Cladophora etc. They show a positive phototactic movement
under diffused light and a negative phototactic movement under intense light.e.g.
Eye spot in algae
C. Thermo-tactic
Such movements result due to an external heat stimulus. For instance, if a large
vessel containing some Chlamydomonas in cold water is warmed on one side, the
Chlamydomonas cells will move and collect towards the warmer side (positive
thermotaxis). However, a negative thermotaxis will occur if the temperature
becomes too high.e.g. Euglena, Chlamydomonas

7. 2. Movements of Curvature –
In this type of movement plant shows movement without changing its position.
In higher plants which are fixed, the movements are restricted only to the bending
or, curvature of some of their parts. Such movements are called as curvature
movements and may be either autonomic i.e., spontaneous or paratonic i.e.,
induced. The curvature movements may be of two types—variation movements
and growth movements. In variation movements the curvature or the bending of
the plant part is temporary while in growth movements it is of permanent nature.It
is divided in 2 types –
I. Autonomous Movements –
Induced by internal Stimuli. e.g. – Desmodium gyrens (Indian Telegraph Plant)
(1) Autonomic movements of variation:
(2) Autonomic Movements of Growth:

8. Autonomic movements of variation:
Telegraph plant (Desmodium gyrans) is an excellent example of such movements. In this plant the
compound leaf consists of a larger terminal and two smaller lateral leaflets (Fig. 21.2). During day
time, the two lateral leaflets exhibit peculiar and interesting movements.
Sometime they move upward at an angle of 90° and come to lie parallel to the rachis. Again, they
may move downward at 180° so that they are parallel to the rachis. They may again move upward at
90° to come in their original position. All these movements occur with jerks after intervals, each
movement being completed in about 2 minutes.

9. • Epinasty & Hyponasty movements of leaves or flowers.
• Epinasty – growth of upper surface of leaf/flower.
• Hyponasty – growth of lower surface of leaf/flower.
(2) Autonomic Movements of Growth:
(i) Hyponastic and epinastic movements:
These movements occur in bifacial organs like young leaves, flower sepals, petals etc., and
result due to the differential growth on the two sides of such organs. For instance, if there
is more growth on the lower side of sepals and petals the flower will close. Such
movements are called as hyponastic movements.
On the other hand, if there is more growth on their upper side the flower will open. Such
movements are called as epinastic movements. Examples of these nastic movements may
be found in ferns where the leaves (fronds) become circinately coiled in young condition
(hyponasty) and erect in older condition (epinasty) or in the opening and closing of
flowers in many plants such as Crocus.

10. (ii) Nutational movements:
Sometimes the growth of the stem apices occurs in a zig-zag manner. It is because the two
sides of the stem apex alternatively grow more. Such growth movements are called as
nutational movements and are common in those stem apices which are not strictly rounded but
flattened.
(iii) Circumnutational movements:
In strictly rounded apices the growth occurs in a rotational way. It is because the region of
maximum growth gradually passes round the growing apex. Such movements are called as
circumnutational movements.

11. II. Induced or Para tonic Movements – It is induced by external stimuli.
Types of Induced movements –
A. Tropic Movements
It is unidirectional movement.
a. Chemo-tropic – movement because of chemical. e.g. Movement of pollen tube
b. Thigmo-tropic – movement because of touch. e.g. movement of suckers & hairs of plant
c. Geotropic – movement because of gravitation. e.g. Root (+), Shoot (-)
d. Phototropic – movement because of light. e.g. Shoot (+), Root (-)
e. Hydrotropic – movement because of water. e.g. Root (+), Shoot (-)
f. Trauma-tropic – movement because of loss or wound.
B. Nastic Movements
a. Seism nasty – movements because of turgor pressure or K+ ions.
e.g. Mimosa pudica
b. Thigmonasty – movements because of touch.
e.g. movements of sensors of pitcher plant
c. Chemonasty – movements because of chemical.
e.g. pitcher plant
d. Nyctinasty – movements because of day & night.
e.g. movements of leaves and flowers

12. HYGROSCOPIC MOVEMENT
• Is movement of part of plant that is caused by the influence of the change of water level from
its cells so happens non-homogenous wrinkling
Example
the breaking of dried Calanchoe pinnata fruit (pacar air)
the opening of sporangium in fern as the cause of wrinkling annulus cells
The opening of sporangium of moss as the cause
of the wrinkling peristome cells
Based on its stimulus, the movements in plant are grouped into three :
1. HYGROSCOPIC MOVEMENT 2. ENDOGENOUS MOVEMENT
3. EXOGENOUS MOVEMENT /ETIONOM

13. ENDOGENOUS MOVEMENT (autonomic)
• • Is movement that is not known yet its cause certainly but predicted this motion is caused by
stimulus that comes from the body of plant itself.
Examples
• the flowing movement of cytoplasm in cell
• the bending movement of leaf bid because of difference of growth velocity
EXOGENOUS MOVEMENT (etionom/esionom)
Is plant movement that it is caused by external stimulus
External stimulus such as :
• Light, gravity, water, touch, and chemical substance

14. The various kinds of exogenous movements in plants
1. Tropism movement 2. Nastic movement 3. Taxis movement
• TROPISM MOVEMENT
• • Is movement of part of plant to stimulus that is movement direction is determined by
the stimulus
• A tropism (from Greek τρόπος, tropos, "a turning") is a biological phenomenon,
indicating growth or turning movement of a biological organism, usually a plant, in
response to an environmental stimulus. In tropisms, this response is dependent on the
direction of the stimulus (as opposed to nastic movements which are non-directional
responses). Tropisms are usually named for the stimulus involved (for example, a
phototropism is a reaction to sunlight) and may be either positive (towards the stimulus)
or negative (away from the stimulus).
• Tropisms occur in three sequential steps. First, there is a sensation to a stimulus, which is
usually beneficial to the plant. Next, signal transduction occurs. And finally, the
directional growth response occurs.
Kinds of tropism
• 1. phototropism 2. geotropism 3. chemotropism 4. thigmotropism
• 5. hydrotropism

15. PHOTOTROPISM
Is tropism movement that caused by stimulus of light
This kind of movement is induced by light. Not all plants and
not all parts respond in the same way to this stimulus. In
general, the stem mostly grows and turns towards the source of
light, while the roots away from it. As shown in fig. the leaves
also positively respond toward the source of light. The leaves,
however, take up such a position in which the broad surface of
the blade is at right angles to the light rays. A stem is, therefore,
said to be positively phototropic, a root negatively phototropic,
and a leaf transversely phototropic or diaphotropic.
Phototropism is also known as heliotropism.
Examples
• the tip of plant that lies in room will bend to direction of
incident light
In certain plants, such as Arachis
hypogea (ground nut) more
complex changes occur within a
short period of time. The flower-
stalks of this plant initially show
positive phototropism until they
have produced flowers. Soon after
fertilization the stalks curl up and
eventually bury the developing
pods under the soil, thus showing
negative phototropism.

16. GEOTROPISM
Is tropism movement that follows earth
gravitational force
• • positive geotropism is geotropism
movement that its direction is downward
• • Negative geotropism is geotropism
movement that its direction upward
Any reaction to the stimulus of earth’s gravity is called geotropism. The effects of gravity on plants
are not like those of light and temperature because it is both continuous in action and constant in
strength. Primary roots and certain other portions of the root system tend to grow directly toward
the centre of gravity and hence called positively geotropic.
Stem mostly grows away from the centre of gravity and is thus negatively geotropic. However,
stems in prostrate plants have lost their negative geotropism and even develop into root stock or
tubers which behave exactly like roots. Most of the leaves take up their positions at right angles to
the centre of gravity and are, therefore, called transversely geotropic or diageotropic. Geotropism is
of three types: orthogeotropism (e.g. primary root), plageotropism (e.g., secondary roots) and
diageocropism (movement of tertiary roots)

17. CHEMOTROPISM
Is tropism movement that is caused by chemical substances stimulus
• Example :
the movement of root to food/fertilizer substance in soil
Certain chemical substances are responsible to bring about curvature movements in plant organs.
For instance, movement of Pollen tube towards ovary due to absorption of calcium and borate
from style of carpel; movement of tentacles in Drosera, closing of lid of Nepenthes due to
nitrogenous food, and penetration of haustoria of parasite into host body etc.

18. Thermotropism:
• Some of the plant organs markedly respond towards fluctuating atmospheric temperature. In
response to this kind of stimulus plant parts exhibit curvature movements in order to take some
advantageous position. Such movements are called thermotropism.

19. Thigmotropism
Is tropism movement that is caused by stimulus of touch to harder thing.
Growth movements made by plants in response to contact with a solid object are
called thigmotropism. These are curvature movements and are most apparently
seen in tendrils and twiners. In most plants the curvatures of the tendrils which
follow contact with a support are mostly the result of increased growth on the
side opposite the stimulus
Example
Tendril of plant movement

20. HYDROTROPISM
Is the movement of plant root that is influenced by
reservation of soil water.
The paratonic curvature movements of growth in
relation to the stimulus of water are called
hydrotropic movements. The tropic response to the
stimulus of water is called hydrotropism. The
roots show positive hydrotropic response, i.e., they
bend towards the water. Hydrotropism is stronger
in roots compared to geotropism.

22. NASTIC MOVEMENT
• • Is plant movement to stimulus, that its direction is not determined by stimulus but by plant
itself
• Nastic movement are directional responses to stimuli (e.g. temperature, humidity, light
irradiance), and are usually associated with plants. The movement can be due to changes in
turgor or changes in growth. Decrease in turgor pressure causes shrinkage while increase in
turgor pressure brings about swelling. Nastic movements differ from tropic movements in that
the direction of tropic responses depends on the direction of the stimulus, whereas the direction
of nastic movements is independent of the stimulus's position. The tropic movement is growth
movement but nastic movement may or may not be growth movement.
• • Kind of nastic movement
• 1. Photonasty
• 2. Nyctinasty
• 3. Thigmonasty
• 4. Thermonasty
• 5. Complex nasty

23. Photonastic
Is nasty movement that its caused by stimulus of light
These movements are induced by fluctuations in the intensity
of light Such movements are exhibited by flowers of several
plants. Many flowers open with the increasing illumination of
the day and close up with the decrease in light intensity.
Flowers of Cestrum nocturnum open at night, and close up with
the dawn of the day.
Example
The opening of Mirabilis jalapa flower at certain time

24. Nyctinasty
Is nasty movement that its caused by dark condition (sleeping movement)
• These movements are commonly called ‘sleeping movements’. Some authors have classified
such movements under the category of photonastic or thermonastic movements. These
movements are induced by alternation of day and night. The leaves of some plants like
Enterobium, clover and oxalis, growing approximately horizontal during the day, begin to
droop and close toward evening and do not rise again until the next morning.
• • Examples
the closing of Butterfly flower ‘s leaves at night
the closing of compound leaves of Leucaena glauca at night

25. Thigmonasty/Seismonasty
Is nasty movement that
• it’s caused by stimulus of touch
These movements are brought about by mechanical stimuli such as contact with a foreign body,
fast wind and rain drops etc. Seismonastic movements are seen in stigmas, stamens and leaves of
many plants. For instance, movements of leaf lets in Mimosa pudica (Biophytum sensitivum and
Neptunia, etc.
Example
• the closing of leaves of Mimosa pudica when touched

26. Thermonasty
Is nasty movement that is caused by temperature stimulus
Such movements are brought about by changes in temperature. Many of the
flower movements are thermonastic. Such flowers open with a rise and close
with a drop in temperature. Sometimes thermonastic movements are
associated with photonastic movements. In both types of responses the
mechanism may be either differential growth, or changes in turgor on upper
and lower sides of the petiole, leaf blade, or perianth part.
Example
• Tulip flower will bloom if suddenly get temperature increased

27. Complex nasty
Is nasty movement that is caused by several factors altogether
Example
the opening and closing of stomata is influenced by light, chemical substance and water
Picture The Opening And Closing Of Stomata

28. • TAXIS MOVEMENT
• • Is transfer movement of all part of plant to stimulus that its direction is determined
by the stimulus
• A taxis (plural taxes/ˈtæksiːz/, from Ancient Greek τάξις (taxis), meaning
'arrangement) is the movement of an organism in response to a stimulus such as light
or the presence of food.
• Taxes are innate behavioural responses. A taxis differs from a tropism (turning
response, often growth towards or away from a stimulus) in that in the case of taxis,
the organism has motility and demonstrates guided movement towards or away from
the stimulus source.
• It is sometimes distinguished from a kinesis, a non-directional change in activity in
response to a stimulus.
Kinds of taxis movement
• 1. phototaxis
• 2. chemotaxis

29. • PHOTOTAXIS
• • Is taxis movement that is caused by stimulus of light
• Phototaxis is a kind of taxis, or locomotory
movement, that occurs when a whole organism
moves towards or away from a stimulus of light.
• This is advantageous for phototrophic organisms as
they can orient themselves most efficiently to receive
light for photosynthesis. Phototaxis is called positive
if the movement is in the direction of increasing light
intensity and negative if the direction is opposite
• • Example
• the movement of chlorophyll to surface/nearer
surface the leaves to get the light

30. Chemotaxis
Is the taxis movement that is caused by
chemical substances stimulus.
Example
movement of spermatozoid of moss and
fern to ovum that is found in
archegonium
attracted to the sugar or protein that is
produced by archegonium

31. What are phytohormones?
Frits Went, 1903-1990 Kenneth Thimann, 1904-1997
“........characterized by the property of serving as
chemical messengers, by which the activity of
certain organs is coordinated with that of others”.
-Frits Went and Kenneth Thimann, 1937
Introduction to Phytohormones
Phytohormones
Phytohormones regulate cellular activities
(division, elongation and differentiation),
pattern formation, organogenesis,
reproduction, sex determination, and
responses to abiotic and biotic stress.

32. Definition
They are various organic compounds other than nutrients produced by plants that
control or regulate germination, growth, metabolism, or other physiological activities.
Also called phytohormone and recently called growth bioregulators.
Plant Hormones & Growth

33. Definition
Plant hormones, which are active in very low concentrations, are produced in certain parts of
the plants and are usually transported to other parts where they elicit specific biochemical,
physiological, or morphological responses.
They are also active in tissues where they are produced. Each plant hormone evokes many
different responses. Also, the effects of different hormones overlap and may be stimulatory or
inhibitory.
The commonly recognized classes of plant hormones are the auxins, gibberellins, cytokinins,
abscisic acid, and ethylene.
Some evidence suggests that flower initiation is controlled by hypothetical hormones called
florigens, but these substances remain to be identified.
A number of natural or synthetic substances such as brassin, morphactin, and other growth
regulators not considered to be hormones nevertheless influence plant growth and
development.

34. Each hormone performs its specific functions; however, nearly all of the measurable
responses of plants to heredity or environment are controlled by interaction between two or
more hormones.
Such interactions may occur at various levels, including
a. The synthesis of hormones,
b.Hormone receptors, and second messengers,
c.Ultimate hormone action.
Furthermore, hormonal interactions may be cooperative, antagonistic, or in balance.
Plant hormones (or plant growth regulators, or PGRs) are internally secreted chemicals in
plants that are used for regulating the plants' growth.
According to a standard definition, plant hormones are:
Signal molecules produced at specific locations, that occur in very low concentrations, and
cause altered processes in target cells at other locations

35. Characteristics
The concentration of hormones required for the
plant response is very low(10-6 to 10-5M),
comparing with the requirement of mineral and
vitamin for plants.
The synthesis of plant hormones is more diffuse
and not always localized.
Classes of Plant Hormones :
It is accepted that there are two major classes of
plant hormones:
What do hormones control in plants?
• Roots and shoots growth
• Seed germination
• Leaf fall
• Disease resistance
• Fruit formation and ripening
• Flowering time
• Bud formation
• Anything related to plant growth!

36. Phytohormones – old timers and
newcomers
Cytokinins Gibberellins
Auxin
Abscisic Acid
Ethylene
Strigolactones
Brassinosteroids
JasmonatesSalicylates

37. Phytohormones regulate all
of the plant life cycle
stages
GerminationFruit
ripening
Seed
dormancyEmbryogenesis
Growth and
branching
Fertilization and
fruit formation
Flower
development

38. Hormones also help plants cope
with
Fruit
ripening
stress throughout their life
Germination
Seed
dormancyEmbryogenesis
Growth and
branching
Fertilization and
fruit formation
Flower
development

39. Most hormones affect most stages
of the plant life cycle
We will examine each hormones within the
context of one of its roles.
Remember that these are merely examples;
most hormones affect most processes in
one way or another.

40. Lecture outline
How hormones work
Hormonal control of vegetative development
Auxin Cytokinins
Strigolactones
Gibberellins
Brassinosteroi
Hormonal control of
reproduction
Ethylene
Abscisic Acid
Hormonal responses to stress
Salicylates
Jasmonates
Cross-regulation of hormonal effects

41. Production of
active hormone
Downstream
effects
Transport
Downstream
effects
H
Binding to
receptor Signal
transduction
Hormones: Synthesis, transport,
perception, signaling and responses

42. HConjugation
De-conjugation
H
Synthesis
Breakdown
Production of
active hormone
Many tightly regulated
biochemical pathways
contribute to active
hormone accumulation.
Conjugation can
temporarily store a
hormone in an inert form,
lead to catabolic
breakdown, or be the
means for producing the
active hormone.
Synthesis

43. Production of
active hormone
Transport
H
Binding to
receptor
Several hormone receptors
have recently been identified.
They can be membrane
bound or soluble
Hormones can move:
• through the xylem or phloem
• across cellular membranes
• through regulated transport proteins
Transport and perception

44. Protein
phosphorylation
P
Protein
dephosphorylation
H
Proteolysis
Signal
transduction
Hormonal signals are
transduced in diverse
ways. Common
methods are
reversible protein
phosphorylation and
targeted proteolysis
Signal transduction

45. Downstream
effects
Transcription
Downstream
effects
Non-genomic effects
(e.g. Ion channel
regulation)
Downstream effects can
involve changes in gene
transcription and changes
in other cellular activities
like ion transport
Responses

46. Conjugation
De-conjugation H
H
Synthesis Breakdown
Production of
active hormone
Downstream
effects
Transcription
Protein
phosphorylationTransport
P Downstream
effects
Non-genomic effects
(e.g. Ion channel
regulation)
Protein
dephosphorylation
H
Proteolysis
Binding to
receptor Signal
transduction
Hormones: Synthesis, transport,
perception, signaling and responses

47. Receptors can be membrane-bound
BrassinosteroidsCytokininsEthylene
P
P
P
Hormone binding initiates an information relay

48. Soluble receptors can facilitate
interactions between proteins
TIR1
Auxin
PYR1
ABA
GA
COI1 JA-
IleGID1
Hormones can act like “molecular glue”

49. Some receptors initiate
proteolysis
protein
The hormones (red) bind to
receptors (green), initiating
proteolysis of repressors
(yellow) to activate a
transcriptional regulator
(blue)
Auxin Gibberellin Jasmonate
Reprinted by permission from Macmillan Publishers, Ltd: NATURE Wolters, H., and Jürgens, G. (2009). Survival of the flexible:
Hormonal growth control and adaptation in plant development. Nat. Rev. Genet. 10: 305– 317. Copyright 2009.

50. Proteolytic targets are covalently
linked to ubiquitin
Ubiquitin
Target
Ubiquitin is a small (76 aa)
protein that targets proteins for
proteolytic cleavage.

51. Hormones affect vegetative growth:
elongation, branching and organogenesis
Elongation in the shoot and
root of a germinating soybean
Organogenesis
Germinated
seedling Growth by
branching
Growth by
elongation
Photo courtesy of Shawn Conley

52. Disrupting hormone synthesis or
response interferes with elongation
Lester, D.R., Ross, J.J., Davies, P.J., and Reid, J.B. (1997) Mendel’s stem length gene (Le) encodes a gibberellin 3-hydroxylase. Plant Cell 9: 1435-1443.;Gray WM
(2004) Hormonal regulation of plant growth and development. PLoS Biol 2(9): e311; Clouse SD (2002) Brassinosteroids: The Arabidopsis Book. Rockville, MD:
American Society of Plant Biologists. doi: 10.1199/tab.0009
Wild type Gibberellin
biosynthesis
mutant
Wild type Auxin
response
mutant
Wild type Brassinosteroid
biosynthesis
mutants
GA
Pea
Auxin
Arabidopsis
Brassinosteroid
Arabidopsis

53. Auxins

Introduction:
 Auxin is a general name for a group of hormones
that are involved with growth responses (i.e.,
elongate cells, stimulate cell division in callus).
 Not surprisingly, the term "auxin" is derived
from the Greek word "to increase or grow".
This was the first group of plant hormones
discovered.

54. Auxins

tryptophan 14
3/2/2014

55. •Growth
•Phototropism and
gravitropism
•Branching
•Embryonic patterning
•Stem cell maintenance
•Organ initiation
Indole-3-acetic acid (IAA), the
most abundant natural auxin
Auxin

56. Auxin controls growth
Site of signal
perception
Site of
response
Coleoptile drawing from Darwin, C., and Darwin, F. (1881) The power of movement in plants. Available online.
Charles Darwin studied
the way seedlings
bend towards light, a
direct effect of auxin
action

57. Darwin concluded that a signal
moves through the plant controlling
growth
“We must therefore conclude that when
seedlings are freely exposed to a lateral
light some influence is transmitted from
the upper to the lower part, causing the
latter to bend.”
Coleoptile drawing from Darwin, C., and Darwin, F. (1881) The power of movement in plants. Available online. Photograph of Darin statue by Patche99z

58. Auxins

Site
Auxin is made in actively growing tissue
which includes young leaves,
especially the shoot apex.
Made in cytosol of cells .
fruits, and
3/2/2014 17

59. Differential cell growth is a result of
auxin movement to the shaded side
Cell
length
Auxin
concentration
Esmon, C.A. et al. (2006) A gradient of auxin and auxin-dependent transcription precedes tropic growth responses. Proc. Natl. Acad. Sci. USA 103: 236– 241.
Friml, J., et al. (2002) Lateral relocation of auxin efflux regulator PIN3 mediates tropism in Arabidopsis. Nature 415: 806-809.
Auxin
accumulation
on shaded side
stimulates
elongation and
bending.

60. Auxins

Site
Auxin is made in actively growing tissue
which includes young leaves,
especially the shoot apex.
Made in cytosol of cells .
fruits, and
3/2/2014 17

61. Auxin moves in part by a
chemiosmotic
Cell wall
mechanism
pH 5.5
Cytoplasm
pH 7
IAA-
IAA- + H+IAAH
IAAH
IAA- + H+
Redrawn from Robert, H.S., and Friml, J. (2009) Auxin and other signals on the move in plants. Nat. Chem. Biol. 5: 325-332.
Auxin is a charged anion (IAA-) in
the cytoplasm (pH 7).
In the more acidic cell wall (pH 5.5)
some is uncharged (IAAH). The
uncharged form crosses the
plasma membrane into the cell
where it is deprotonated and
unable to exit other than through
specific transporters.

62. Polar auxin transport
Cell wall
pH 5.5
Cytoplasm
pH 7
IAA-
IAA- + H+IAAH
Net flow
of auxin
IAAH
IAA- + H+
Redrawn from Robert, H.S., and Friml, J. (2009) Auxin and other signals on the move in plants. Nat. Chem. Biol. 5: 325-332.
Auxin transport out of cells is
controlled by three families of
transport proteins that collectively
control the directionality of auxin
movement. Asymmetric distribution
of the transporters controls polar
auxin transport.

63. Auxin biosynthesis
Indole
Tryptophan
Indole-3-
pyruvic acid
(IPA)
Tryptamine Indole-3-
acetamide
(IAM)
Indole-3-
acetaldoximine
(IAOx)
Indole-3-
acetaldehyde
IAA
Adapted from Quittenden, L.J., Davies, N.W., Smith, J.A., Molesworth, P.P., Tivendale, N.D., and Ross, J.J.
(2009). Auxin biosynthesis in pea: Characterization of the tryptamine pathway. Plant Physiol. 151: 1130-1138..
IAA is produced from
tryptophan (Trp) via several
semi-independent pathways and
one Trp-independent pathway.
Environmental and
developmental control of the
genes controlling auxin
biosynthesis, conjugation and
degradation maintain auxin
homeostasis.

64. Auxin regulates plant development
Wolters, H., and Jürgens, G. (2009). Survival of the flexible: Hormonal growth control and adaptation in plant development. Nat. Rev. Genet. 10: 305– 317.
Promote branching
in the root
Maintain stem cell fate
at the root apical
meristem
Patterning and vascular
development
Inhibit branching in
the shoot
Lateral organ initiation at the
shoot apical meristem

65. Many
by
of auxin’s effects are mediated
changes in gene expression
Genes controlling
cell growth
Genes involved in
signaling
Genes coordinating other
hormone response
pathways
Wolters, H., and Jürgens, G. (2009). Survival of the flexible: Hormonal growth control and adaptation in plant development. Nat. Rev. Genet. 10: 305– 317.

66. 19
Auxin Actions
1. Cellular Elongation:


Auxin can induce and amplify proton pumping.
Acidified cell walls have increased elasticity which
lead to cell elongation.

67. Auxin Actions

2. Cell differentiation
Auxin promotes differentiation of vascular
xylem & phloem):
tissue (i.e.,
 Auxin
Auxin
Auxin
 Auxin
and
and
and
and
sugar -----> Vascular tissue
low sugar (1.5 - 2.5%) -----> Xylem
high sugar (4%)
moderate levels
------->- Phloem
of sugar (2.5 - 3.0%) ----->-
Xylem & Phloem
3/2/2014 20

68. Auxin Actions
3. Ethylene production
 IAA apparently stimulates
ethylene.
4. Inhibition of root growth
the production of
 [IAA] > 10-6 M inhibit root elongation.
 However, very low [IAA]
elongation.
(>10-8 M) favor root
5. Stimulate root initiation (lateral roots,
adventitious roots)
Roots always form at the basal end of cutting
3/2/2014
21

69. Auxin
Formation of
Actions

adventitious roots
3/2/2014 22

70. Auxin Actions

6. Flowering
Although most plants don’t initiate the
production of flowers after auxin treatment,
pineapple and its relatives (Bromeliaceae) do.
 Once flowers are initiated, in many species,
IAA promotes the formation of female flowers.
3/2/2014 23

71. Auxin Actions

7. Parthenocarpic fruit development
 Pollination of the flowers of angiosperms initiates
the formation of seeds.
As the seeds mature, they release auxin to the
surrounding flower parts, which develop into the
fruit that covers the seeds.
Some commercial growers deliberately initiate fruit
development by applying auxin to the flowers. Not
only does this ensure that all the flowers will "set"
fruit, but it also maximizes the likelihood that all the
fruits will be ready for harvest at the same time.


24
3/2/2014

72. Auxin Actions

Auxin produced by seeds promotes
tissue growth
ovary
3/2/2014 25

73. Auxin Actions
8- Apical Dominance
 Lateral branch growth are inhibited near the shoot
apex, but less so farther from the tip.
Apical dominance is disrupted in some plants by
removing
bushy.
the shoot tip, causing the plant to become
3/2/2014 26

74. Auxin Actions
8- Apical Dominance
Plant b has apical bud removed so3/2/2014 27
axillary buds grow

75. Auxin Actions

10- Tropic responses
Such as gravitropism and phototropism
A-Phototropism
 is a growth
stimulus
movement induced by a light
3/2/2014 28

76. Auxin Actions
Phototropism
Sunlight breaks down auxin
Plant stems indirect sunlight
least amount of auxin
will have the
Area of the plant that is more shaded
have more auxin
will
More
Plant
cell growth on shaded side
bends towards light
3/2/2014 29

77. Auxin Actions
Phototropism

 Greater light on
side of the plant
the right Light directly
plant
 Auxins are in
quantity
over the
 Auxin quantity becomes
greater on the left cell
 Auxins trigger cell
equal
elongation on the left side Cell elongation is equal
on all sides of the cell
30
 Plant ‘stretches’ to the
3/2/2014

78. Auxin Actions

Geotropism or Gravitropism
 The plant stem that was once upright is on its side
 The auxin are settle on the bottom side of the stem
 More auxin accumulate on the stems bottom side
 More cell growth occurs on bottom side
 Plant bends upward
 A growth response to gravity which causes roots to
grow downward and shoots to grow upward
3/2/2014 31

79. 
Auxin Actions
Gravitropism3/2/2014 32

80. Auxin Actions

Gravitropism
3/2/2014 33

81. Cytokinins
Site:
Synthesized primarily in the
of the roots.
meristematic region
This is known in part because roots can be
cultured (grown in Artificial medium in a flask)
without added cytokinin, but stem cells cannot.
 Cytokinins are also produced in developing
embryos .3/2/2014 48

82. Cytokinins

Transport:
 Via xylem (transpiration stream).
 Zeatin ribosides are the main transport form;
converted to the free base or glucosides in
leaves.
 Some cytokinin also moves in the phloem.
the
3/2/2014 49

83. •Cell division
•Control of leaf
senescence
•Control of nutrient
allocation
•Root nodule
development
•Stem cell maintenance
•Regulate auxin action trans-zeatin, a cytokinin
Cytokinins

84. Cytokinins are a
adenine-like
family of related
compounds
dihydrozeatin cis-zeatin
Isopentenyl adenine trans-zeatin
Hirose, N., Takei, K., Kuroha, T., Kamada-Nobusada, T., Hayashi, H., and Sakakibara, H. (2008). Regulation of cytokinin
biosynthesis, compartmentalization and translocation. J. Exp. Bot. 59: 75– 83.

85. Cytokinin (CK) biosynthesis
Regulated
by CK and
nitrogen Tissue specific;
auxin, CK and
ABA sensitive
Meristem
specific
Inactive form
Upregulated by
CK andABA
Hirose, N., Takei, K., Kuroha, T., Kamada-Nobusada, T., Hayashi, H., and Sakakibara, H. (2008). Regulation of cytokinin
biosynthesis, compartmentalization and translocation. J. Exp. Bot. 59: 75– 83.
CKX
CK biosynthesis
and inactivation
are strongly
regulated by CK,
other hormones
and exogenous
factors.

86. Cytokinins
Site:
Synthesized primarily in the
of the roots.
meristematic region
This is known in part because roots can be
cultured (grown in Artificial medium in a flask)
without added cytokinin, but stem cells cannot.
 Cytokinins are also produced in developing
embryos .3/2/2014 48

87. Cytokinins

Transport:
 Via xylem (transpiration stream).
 Zeatin ribosides are the main transport form;
converted to the free base or glucosides in
leaves.
 Some cytokinin also moves in the phloem.
the
3/2/2014 49

88. Cytokinins
1- Control morphogenesis
Actions
In plant tissue cultures, cytokinin is required for the
growth
cells):
of a callus (an undifferentiated, tumor-like mass of
Ratio of cytokinin and auxin are important in determining
the fate of the callus:
The concentration The callus differentiation
callus + low [cytokinin/auxin] callus grows well, forms roots
callus + high [cytokinin/auxin] callus grows well, forms meristem & shoots
The Medium The callus differentiation
callus + auxin + no cytokinin little growth of callus
callus + auxin + cytokinin callus grows well, undifferentiated

89. Cytokinins Actions
1- Control morphogenesis
51

90. Cytokinins

Actions
2- Regulates the cell cycle/cell division
 (hence, the name "cytokinins) –especially by
controlling the transition from G2 mitosis.
This effect is moderated by cyclin-dependent
protein kinases (CDK's) and their subunits,
cyclins.
3/2/2014 52

91. Cytokinins
3- Bud development
Actions
 Direct application of cytokinin promotes
of axillary buds
 Exogenous cytokinin and auxin are thus
the growth
antagonistic in their effects on axillary bud growth
17-53

92. Cytokinins
4- Delay senescence
Actions
 Senescence is the
programmed aging process
that occurs in plants.
Loss of chlorophyll, RNA,
protein and lipids.
Cytokinin application to an
intact leaf markedly reduces
the extent and rate of
chlorophyll and protein
degradation and leaf drop.


3/2/2014 54

93. Cytokinins

5- Greening
Actions
 Cytokinins promotes the light-induced formation of
chlorophyll and conversion of etioplasts to
chloroplasts (greening process).
3/2/2014 55

94. 56
Cytokinins

Actions
6. Promote cell expansion
 Cytokinins stimulate the
expansion of cotyledons.
 The mechanism is
associated with increased
plasticity of the cell wall, not
associated with acidification.
3/2/2014

95. Cytokinins act antagonistically to
auxins
the shoot
branching inPromote
differentiation
apical
Reprinted by permission from Macmillan Publishers, Ltd: NATURE Wolters, H., and Jürgens, G. (2009). Survival of the flexible:
Hormonal growth control and adaptation in plant development. Nat. Rev. Genet. 10: 305– 317. Copyright 2009.
Promote
at the root
meristem
Maintain stem
cell fate at the
root apical
meristem
Inhibit
Promote
branching t
in the root
he shoot
Promote
branching in
Inhibit
branching in
the shoot
Auxin
Promote lateral
organ initiation
at the shoot
apical
meristem
CK
Promote stem
cell fate at the
shoot apical
meristem

96. Auxin and cytokinin regulate each
other’s function at the root apex
Auxin
transportCell
differentiation
Cell
division Cytokinin
Auxin transport
and response
Cytokinin
biosynthesis
Auxin
Through effects on each other’s synthesis,
transport and response, auxin and cytokinin
establish two mutually exclusive domains that
coordinate cellular activities at the root apex.

97. Auxin, cytokinin and strigolactones
control branching
promoted by CK
Coleus shoot image by Judy Jernstedt, BSA ; lateral root image from Casimiro, I., et al. (2001) Auxin
transport promotes Arabidopsis lateral root initiation. Plant Cell 13: 843-852.
Shoot branches are
and inhibited by
auxin and
strigolactones
Branching controls
every aspect of
plant productivity
from nutrient uptake
to crop yields.
Root branches,
called lateral roots,
are promoted by
auxin and inhibited
by CK

98. Cytokinin control of gene
expression in Arabidopsis
Receptor
D D
HPt H
D
A-ARR or
C-ARR D
B-ARR
Transcription
Type B Arabidopsis response regulators
(ARRs) are transcription factors. Type A or
C ARRs interfere with CK signaling through
as yet unknown means.
HH

99. Cytokinins affect grain production
and drought tolerance
Ashikari, M. et al. (2005) Cytokinin oxidase regulates rice grain production. Science 309: 741 – 745, with
permission from AAAS; Rivero, R. M. et al. (2007) PNAS 104: 19631-19636.
Wild-type Elevated CK
Tobacco plants that produce
more CK are more drought
tolerant because of the
delay in leaf senescence
conferred by CK.
Rice plants that
accumulate more
CK can produce
more grain per plant
because of changes
in inflorescence
architecture.

100. Host plant
Image source USDA APHIS PPQ Archive ; Reprinted from Tsuchiya, Y., and McCourt, P. (2009). Strigolactones: A new
hormone with a past. Curr. Opin. Plant Biol. 12: 556– 561 with permission from Elsevier.
Strigolactones, synthesized from carotenoids,
are produced in plant roots. They attract
mycorrhizal fungi and promote the germination
of parasitic plants of the genus Striga.
Striga seeds
Current Opinion in Plant Biology
Strigolactones

101. Strigolactones inhibit
outgrowth
branch
WT Mutant
Apex
Bud
Auxin Strigolactone
Lin, H., et al. (2009) DWARF27, an iron-containingprotein required for the biosynthesis of strigolactones,
regulates rice tiller bud outgrowth. Plant Cell 21: 1512-1525.
In a rice mutant that
does not produce
strigolactones, tillers
(lateral branches)
grow out as shown.
Auxin transported from
the shoot to the root
induces strigolactone
synthesis, which indirectly
inhibits bud outgrowth.

102. Gibberellins

3/2/2014 34

103. Gibberellins

 Gibberellins are plant hormones that promote
growth, seed germination and leaf expansion.
They occur at low concentrations in vegetative
tissues but at higher concentrations in
germinating seeds.
Induce cell elongation and cell division.
Important for plant growth and development
through flowering and/or seed germination.
3/2/2014 35

104. Gibberellins
Site :
 Young leaves, roots, and developing
(developing endosperm) and fruits.
Transport :
seeds
 Made in the tissue in which it is used
 Transport occurs through xylem, phloem,
cell.
or cell-to-
 Phloem seems to be most important transport route
 Transport is not polar, as it is for auxin.
3/2/2014
36

105. Gibberellins Actions
1- Promotes stem elongation

 When applied to intact plants, GA usually causes
increase, unlike auxin.
an
 It overcomes dwarfism in mutants that have a
mutation in the GA synthesis
dwarf = short;
wild type = tall ;
dwarf + GA = tall.
 Thus, GA application:
pathway.
(1) stimulates elongation; and
(2) acts on intact plants.
37
3/2/2014

106. Gibberellins Actions
1- Promotes stem elongation
3/2/2014 38

107. Gibberellins Actions
2- Overcomes dormancy in seeds
 Gibberellins also have a fundamental role in breaking
dormancy and stimulating germination.
The endosperm of many seeds contains protein and
seed

carbohydrate reserves upon which a developing embryo
relies for energy and nutrition.
These reserves must be mobilised and transported to the
embryo.
A range of hydrolytic and proteolytic enzymes break down
endosperm starches and proteins into smaller, more easily
transported molecules, such as sugars and amino acids.


39
3/2/2014

108. Gibberellins Actions
2- Overcomes dormancy in seeds
40

109. Gibberellins

Actions
3- Involved in parthenocarpic fruit development
3/2/2014 41

110. Gibberellins Actions

4- GA can induce fruit enlargement
External
application of
gibberellins can
also enlarge fruit
size in grapes
3/2/2014 42

111. Gibberellins Actions
5- Promotes cell
division & elongation
3/2/2014 43

112. Gibberellins

Actions
6- Flowering
 GA stimulates bolting in Long Day plants
treatments
and can
substitute for long days or cold that are
necessary for flowering.
3/2/2014 44

113. Gibberellins

Actions
7-Sex expression
In plants with separate male and female
flowers, GA application can determine sex.
 For example, in cucumber and spinach, GA
treatment increases the proportion of male
flowers.
 In maize, GA treatment causes female flower
development.
3/2/2014 45

114. •Growth
•Seed germination
•Promote flowering
•Promote sex
determination
species
•Promote fruit
in some
A Gibberellin (GA4)
growth
Gibberellins

115. Gibberellins are a family
compounds
of
GA4 is the major active
GA in Arabidopsis
Sun T (2008) Gibberellin metabolism, perception and signaling pathways in Arabidopsis: September 24, 2008. The Arabidopsis Book. Rockville,
MD: American Society of Plant Biologists. doi: 10.1199/tab.0103
Only some GAs are
biologically active. The
major bioactive
gibberellins are shown
here.

116. Major GA biosynthetic and catabolic
pathways in higher plants
Inactivation
Olszewski, N., Sun, T.p., and Gubler, F. (2002) Gibberellin Signaling: Biosynthesis, Catabolism, and Response Pathways Plant Cell 14: S61-S80
Active

117. Gibberellins regulate growth
Inactivation
Lester, D.R., Ross, J.J., Davies, P.J., and Reid, J.B. (1997) Mendel’s stem length gene (Le) encodes a gibberellin
3-hydroxylase. Plant Cell 9: 1435-1443.
Wild type Gibberellin
biosynthesis
mutant le
Active
The pea mutant le, studied by
Mendel, encodes GA3 oxidase, which
produces active GA. Loss of function
of le reduces active GA levels and
makes plants dwarfed.

118. Genes controlling GA synthesis are
important “green revolution” genes
Tremendous increases in crop
yields (the Green Revolution)
20thduring the century
occurred because of increased
use of fertilizer and the
introduction of semidwarf
varieties of grains.
The semidwarf varieties put
more energy into seed
production than stem growth,
and are sturdier and less likely
to fall over.
Photos courtesy of S. Harrison, LSU Ag center and The World Food Prize.
Distinguished plant breeder and Nobel Laureate
Norman Borlaug 1914-2009

119. Several of the green revolution
genes affect GA biosynthesis
Wild-type Semidwarf
Reprinted by permission from Macmillan Publishers, Ltd. (Nature) Sasaki, A., et al. (2002) Green revolution: A mutant gibberellin-synthesis gene in rice Nature 416: 701-
702, copyright 2002.; Olszewski, N., Sun, T.p., and Gubler, F. (2002) Gibberellin sgnaling: Biosynthesis, catabolism, and response pathways Plant Cell 14: S61-S80.
Semidwarf rice varieties
underproduce GA because
of a mutation in a the GA20
oxidase biosynthetic gene.
Active

120. A gene affecting DELLA protein
stability is a “green revolution” gene
GA
rht1
Reprinted by permission of Macmillan Publishers, Ltd. Peng, J., et al. (1999) 'Green
revolution' genes encode mutant gibberellin response modulators. Nature 400: 256-261.
Dwarf rht1
rht1
The wheat Rht1 locus encodes
a DELLA protein. The dwarf
allele lacks the DELLA domain
and resists proteolysis.
Wild-type
GA
Rht1
DELLA
Transcription

121. Brassinosteroids

BR-deficient mutants exhibit dramatic
growth defects, including dwarfism, reduced
apical dominance and male fertility, as well
as delayed senescence and flowering
Brassinosteroids switch on specific genes by
inactivating a protein that otherwise
indirectly blocks transcription of those genes


17-74

122. Brassinosteroids

Fig. 17.20: Signal transduction chain for the response to
brassinosteroids3/2/2014 75

123. •Cell elongation
•Pollen tube growth
•Seed germination
•Differentiation of
vascular tissues and
root hairs
•Stress tolerance
Brassinolide, the
most active
brassinosteroid
Brassinosteroids

124. Brassinosteroid (BR)
dwarfed
mutants are
Tomato
Pea
Bishop, G. J., and Koncz, C. Brassinosteroids and plant steroid hormone signaling. (2002) Plant Cell14: S97-S110.
Arabidopsis
BRs promote cell elongation
in part by loosening cell walls
Cell wall
loosening
Lowered resistance to internal
turgor pressure; cell expansion

125. Reducing BR signaling
dwarf barley
H
produces
H
Wild-type
uzu
Chono, M., et al., (2003) A semidwarf phenotype of barley uzu results from a nucleotide substitution in
the gene encoding a putative brassinosteroid receptor Plant Physiology 133:1209-1219.
Less cell
elongation
Cell
elongation
The uzu plants have a
missense mutation in the
BR receptor, making them
less sensitive to BR. This is
the first dwarf grain
produced through
modification of BR
signaling.

126. Plant hormones have diverse effects
on plant growth.
Auxin, gibberellins and
brassinosteroids contribute to
elongation growth.
Auxin, cytokinins and strigolactones
regulate branching patterns.
Growth and branching profoundly
affect crop yields.
Summary – hormonal control of
vegetative growth

127. In
•
angiosperms:
transition from vegetative to
reproductive growth
flower development,
fruit development and
ripening
seed development,
maturation and germination
•
•
•
Photo courtesy of Tom Donald
Hormonal control of reproductive
development

128. Transition to flowering
The decision to reproduce is tightly
controlled by environmental and
hormonal factors. For many plants day-
length is critical in this transition, but
other plants are day-length neutral.
Similarly, some plants absolutely require
specific hormonal signals which have
little or no effects on other plants.
Lithops flowering

129. GA’s role in initiating flowering
varies by species and growth-habit
Arabidopsis thaliana
Annual
Lolium temulentum
Annual temperate grass
Yes
Beta vulgaris
Biennial
Yes
Malus domestica
Perennial
No Short Days
Yes
Long Days
No
Photos courtesy of Plate 271 from Anne Pratt's Flowering Plants, Grasses, Sedges and Ferns of Great Britain c.1878,
by permission of Shrewsbury Museums Service; David Kuykendall ARS; Vincent Martinez; Takato Imaizumi.

130. pineapple is a fruit
roduced from
neapple flowers.
ommercial growers
eat the plants with
hylene to
nchronize flowering.
Ethylene promotes flowering in
pineapples and other bromeliads
A
p
pi
C
tr
et
sy

131. Flower development
Hormones contribute to
flower development in
many ways:
• Patterning of the
floral meristem
Outgrowth of organs
Development of the
male and female
gametophytes
Cell elongation
•
•
•

132. Ethylene and gibberellins are
involved in sex determination
Hermaphrodite Male Female
Image courtesy of Abdelhafid Bendahmane, URGV - Plant Genomics Research INRA

133. Fruit development and ripening are
under hormonal control
Pollination initiates petal
senescence, cell division
and expansion in the
ovary to produce a fruit,
and fruit ripening.

134. Auxin and
and
GA promote cell division
growth of the fruit
Auxin + GA
GA
Auxin
Seedless varieties of grapes
and other fruits require
exogenous application of GA for
fruit development. Strawberry
receptacles respond to auxin.

135. Fruit ripening is induced by ethylene
Auxin
GA
Ethylene
Ethylene is a gaseous hormone
that promotes fruit softening and
flavor and color development

136. Ethylene

H
C
/
H
H
/
C
H
=
3/2/2014 63

137. Ethylene

Ethylene is the only gaseous plant hormone (C2H4)
It is produced naturally by higher plants and is able to
diffuse readily, via intercellular spaces, throughout
the entire plant body
Ethylene is involved primarily in plant responses to
environmental stresses such as flooding and drought,
and in response to infection, wounding and
mechanical pressure
It also influences a wide range of developmental
processes, including shoot elongation, flowering, seed




germination, fruit ripening and leaf abscission and
senescence
3/2/2014 64

138. Ethylene Action
1- Ethylene—signal transduction

 Several transmembrane
proteins have been
identified that bind to
ethylene at the cell
surface and function
signal transducers.
as
17-65

139. Ethylene
2- Ethylene—fruit ripening
Action
 Under natural conditions, fruits undergo a series
changes, including changes in colour, declines in
acid content and increases in sugar content
of
organic
 In many fruits, these metabolic processes often coincide
with a period of increased respiration, the respiratory
climacteric
During the climacteric there is also a dramatic increase in
ethylene production
Ethylene can initiate the climacteric in a number of fruits
and is used commercially to ripen tomatoes, avocados,
melons, kiwi fruit and bananas


3/2/2014 66

140. 673/2/2014
Ethylene Action
2- Ethylene—fruit ripening

141. Ethylene
3- Ethylene—Shoot Growth
Action


Applied ethylene has the capacity to influence shoot growth
Application of ethylene to dark-grown seedlings can cause
reduced elongation of the stem, bending of the stem and
swelling of the epicotyl or hypocotyl.
3/2/2014 68

142. Ethylene

Action
4- Ethylene—flowering
 The ability of ethylene to affect flowering
pineapples has important commercial
applications.
in
 Ethylene also promotes flower senescence
(ageing) in plants such as petunias, carnations
and peas.
3/2/2014 69

143. Ethylene Action
4- Ethylene—flowering
3/2/2014 70

144. Ethylene Action
 (b)(a)
Fig. 17.19: Senescence in carnations
3/2/2014 71

145. Ethylene Action
5- Thigmomorphogenesis
 The change in growth form in response to a
mechanical stimulation such as touch.
3/2/2014

146. •Control of fruit ripening
•Control of leaf and
petal senescence
•Control of cell division
and cell elongation
•Sex determination in
some plants
•Control of root growth
•Stress responses
H
C2H4
C2H4
Ethylene induces the triple
•reduced elongation,
•hypocotyl swelling,
•apical hook exaggeration.
response:
H
C C
H H
Ethylene

147. Ethylene promotes senescence
petals
of
leaves and
In gas-lit houses,
plants were harmed
by the ethylene
produced from
burning gas.
Aspidistra is
ethylene- resistant
and so became
popular houseplant.
Beyer, Jr., E.M. (1976)A potent inhibitor of ethylene action in plants. Plant Physiol. 58: 268-271.
Air (control) 7 days ethylene
Cotton plants
Ethylene promotes
leaf and petal
senescence.

148. Ethylene shortens the longevity
fruits
of
cut flowers and
Strategies to limit ethylene effects
Limit production - high CO2 or low O2
Removal from the air -KMnO4 reaction, zeolite absorption
Interfere with ethylene binding to receptor - sodium
thiosulfate (STS), diazocyclopentadiene (DACP), others
Reprinted from Serek, M., Woltering, E.J., Sisler, E.C., Frello, S., and Sriskandarajah, S. (2006) Controlling ethylene
responses in flowers at the receptor level. Biotech. Adv. 24: 368-381 with permission from Elsevier.
Ethylene levels can be
managed to maintain
fruit freshness,
commercially and at
home.

149. Molecular genetic approaches can
limit ethylene synthesis
ACC
synthase
ACC
oxidase H H
C C
H H
ACC
(1-aminocyclopropane-1-
carboxylic acid)
S-adenosyl
methionine
Ethylene
Antisense
ACC synthase
Introduction of antisense
constructs to interfere with
expression of biosynthesis
enzymes is an effective way
to control ethylene production.Control
Theologis, A., Zarembinski, T.I., Oeller, P.W., Liang, X., and Abel, S. (1992) Modification
of fruit ripening by suppressing gene expression. Plant Phys. 100: 549-551.

150. Ethylene-regulated gene expression
is negatively regulated
EthyleneAir
Air
Receptor
CTR
Benavente, L.M., and Alonso, J.M. (2006) Molecular mechanisms of ethylene signaling in Arabidopsis. Mol. BioSyst. 2: 165– 173. Reproduced by
permission of The Royal Society of Chemistry (RSC) for the European Society for Photobiology, the European Photochemistry Association, and the
RSC. Diagram adapted from Cuo, H., and Ecker, J.R. (2004) The ethylene signaling pathway: new insights. Curr. Opin. Plant Biol. 7: 40-49.
In the absence of
ethylene, CTR binds
the receptor and
prevents transcription.
Ethylene binding to
the receptor releases
CTR, permitting
transcription.

151. Ethylene perception mutants
interfere with ripening
Air or
Ethylene
Receptor
CTR
Barry, C. S., et al. (2005) Ethylene insensitivity conferred by the Green-ripeand Never-ripe 2 ripening mutants of tomato. Plant Physiol. 138: 267-275.
Several mutations
that affect ethylene
perception and
signaling interfere
with fruit ripening.
Wild type
Green-ripe
Never-ripe2
Never-ripe

152. Abscisic

acid
Inhibits growth
Promotes dormancy
Closes stomata
Produced in response to stress.
3/2/2014 57

153. Abscisic

acid
Sites :
Plastids
 Most tissues,
Transport :
especially leaves and seeds
 Xylem and phloem (greater amounts)
3/2/2014 58

154. Abscisic acid Actions

1- ABA—drought resistance
 Abscisic acid is the key internal signal that facilitates
drought resistance in plants
Under water stress conditions, ABA accumulates in
leaves and causes stomata to close rapidly, reducing
transpiration and preventing further water loss.

 K+ABA causes the opening of efflux channels in
guard cell plasma membranes, leading to a huge loss
of this ion from the cytoplasm.
 The simultaneous
decrease in guard
of stomata.
osmotic loss of water leads to a
cell turgor, with consequent closure
59
3/2/2014

155. Abscisic acid

Actions
2- ABA—freezing resistance
 Elevated ABA levels are associated with increased
freezing resistance.
ABA appears to mediate a plant’s response to
environmental stresses, such as freezing, by
regulating gene expression.
Certain genes are switched on by ABA while
others are switched off.


3/2/2014 60

156. Abscisic acid
3- ABA—Seed Dormancy
Actions


ABA plays a major role in seed dormancy
During seed maturation, ABA levels increase
dramatically.
This inhibits germination and turns on the production of
proteins that enable the embryo to survive dehydration
during seed maturation
As dormancy can only be broken by specific
environmental cues, it ensures that a seed will
germinate only under suitable conditions of moisture,
light and temperature

 The breaking of dormancy is associated with a decline
the level of ABA
in
61
3/2/2014

157. Abscisic acid

Actions
Fig. 17.15: Celmisia aseriifolia (snow daisy)3/2/2014 62

158. •Seed maturation and
dormancy
•Desiccation tolerance
•Stress response
•Control of stomatal
aperture
Abscisic acid

159. ABA accumulates in maturing seeds
Embryonic
patterning
Reserve
accumulation
Desiccation
tolerance
Seed maturation
requires ABA
synthesis and
accumulation of
specific proteins
to confer
desiccation
tolerance to the
seed.

160. ABA synthesis and signaling is
required for seed dormancy
ABA
Protein
Kinase
Transcription
Factor
Transcription
Loss of function of
ABA signaling
(protein kinase or
transcription factor
function) interferes
with ABA-induced
dormancy and
causes precocious
germination.

161. Once dormant and dry, seeds can
remain viable for very long times
Date palm growing
from 2000 year
seed.
old
From Sallon, S., et al. (2008). Germination, genetics, and growth of an ancient date seed. Science 320: 1464, with permission from AAAS Lotus picture by Peripitus
These date palm seeds are nearly
2000 years old, but still viable and
capable of germination. Five
-hundred year old lotus seeds have
also been successfully germinated.
Having a thick seed coat may help
these super seeds retain viability.

162. GA is required for seed germination
Reserve
mobilization
Cell
expansion
GA
ABA
Seed germination
requires elimination
of ABA and
production of GA to
promote growth
and breakdown of
seed storage
products.

163. GA is used by brewers to promote
barley germination
Breakdown of starch in the
endosperm is initiated by GA
produced by the endosperm or
added during the malting process.
GA
GA
sugars starch
Embryo
Endosperm Aleurone
Images by Prof. Dr. Otto Wilhelm Thomé Flora von Deutschland, Österreich und der Schweiz 1885 and Chrisdesign.
amylase

164. GA and ethylene promote flowering in some
plants.
Fruit growth, maturation and ripening are
regulated by auxin, GAand ethylene.
Seed maturation and germination are
regulated by ABA and GA.
Understanding the roles of hormones in plant
reproduction is important for food production,
because most of our caloric intake is derived
from seeds.
Summary – hormonal regulation of
reproductive development

165. Air pollution
Photooxidative
stress
Wounding and
mechanical
damage
High
temperature
stress
Water deficit,
drought
Soil salinity
Cold and
freezing
stress
Reprinted by permission from Macmillan Publishers, Ltd. Nature Chemical Biology. Vickers, C.E., Gershenzon, J., Lerdau, M.T., and Loreto, F.
(2009) A unified mechanism of action for volatile isoprenoids in plant abiotic stress Nature Chemical Biology 5: 283 - 291 Copyright 2009.
Plants’ lives are
very stressful.....
ABA and ethylene
help plants
respond to stress.
Hormonal responses to abiotic
stress

166. ABA biosynthesis is
regulated
strongly
Reprinted from Nambara, E., and Marion-Pol, A. (2003) ABA action and interactions in
seeds. Trends Plant Sci. 8: 213-217 with permission from Elsevier.
ABA levels are tightly controlled.
Critical steps in ABA biosynthesis
(circled in red) are encoded by
multiple tightly regulated genes to
ensure rapid and precise control.

167. ABA synthesis is strongly induced
in response to stress
[ABA]
µg/g dry
weight
Leaf
water
potential
(atm)
Hours of drought stress
R.L. Croissant, , Bugwood.org www.forestryimages.org . Zabadel, T. J. (1974) A water potential
threshold for the increase of abscisic acid in leaves. Plant Physiol. (1974) 53: 125-127.
ABA levels rise during drought stress
due in part to increased biosynthesis

168. H2O2
ABA induces stress-responsive
genes
Osmoprotectants
(sugars, proline,
glycine betaine)
Membrane and
protein stabilization
(HSPs, LEAs)
Movement of
water and ions
(aquaporins, ion
channels)
Oxidative stress responses
– peroxidase, superoxide
dismutase
O2¯

169. ABA binding to an intracellular
receptor initiates transcriptional
responses
Reprinted by permission of Macmillan Publishers Ltd. Miyazono, K., et al. (2009) Structural basis of abscisic acid signalling. Nature 462: 609-614.
PYL1 is an ABA receptor.
When PYL1 binds ABA, it
also binds the protein
phosphatase PP2C,
inhibiting its function.

170. ABA signal transduction
gene expression
affects
inactivation of the PP2C
kinase (e.g. SnRK) to
transcription of ABA-inducible
When ABA is present,
phosphatase permits a protein
phosphorylate and activate
ABA-inducible TFs, promoting
genes.
Low ABA
PYL1
PP2C
TF
SnRK
High ABA
ABA
PYL1
PP2C
P
P
Transcription

171. ABA regulates stomatal aperture by
changing the volume of guard cels
Pairs of guard cells
surround the
openings of plant
pores called stomata.
Guard cell image © John Adds, obtained through the SAPS Plant Science Image Database.
Guard cells control the opening and closing of stomata to
regulate gas exchange: a fine balance is required to allow
CO2 in for photosynthesis and prevent excessive water loss.
Image buYizhou Wang, University of Glasgow

172. ABA controls stomatal aperture by
changing the volume of guard cels
When stomata are open, plants lose water through
transpiration. ABA induced by drought causes the guard cells to
close and prevents their reopening, conserving water.
Sirichandra, C., Wasilewska, A., Vlad, F., Valon, C., and Leung, J. (2009)The guard cell as a single-cell model towards understandingdrought tolerance and abscisic
acid action. Journal of Experimental Botany 2009 60: 1439-1463. © The Author [2009]. Published by Oxford University Press on behalf of the Society for
Experimental Biology.

173. ABA-induced stomatal closure is
extremely rapid and involves
changes in ion channel activities
out
Cl-
in
A- channel
K+
in channel
K+
H2O
Adapted from Kwak JM, Mäser P, Schroeder JI (2008) The clickable guard cell, version II: Interactive model of guard cell signal
transduction mechanisms and pathways. The Arabidopsis Book, ASPB. doi: 10.1199/tab.0114.
ABA triggers an increase in cytosolic
calcium (Ca2+), which activates anion
channels (A-) allowing Cl- to leave the cell.
ABA activates channels that move
potassium out of the cell (K+ ) and inhibits
channels that move potassium into the cell
(K+ ). The net result is a large movement
of ions out of the cell.
As ions leave the cell, so does water (by
osmosis), causing the cells to lose volume
and close over the pore.

174. Jasmonates
insects, other
Necrotrophic
Salicylic Acid
Photo credits: A. Collmer, Cornell University; Salzbrot.
Herbivores –
animals, fungi –
organisms
Bacteria,
fungi,
viruses –
Biotrophic
organisms
Hormonal responses to biotic stress

175. •Response to
necrotrophic pathogens
•Induction of anti-
herbivory responses
•Production of
herbivore-induced
volatiles to prime other
tissues and attract
predatory insects
Jasmonates

176. JA biosynthesis
Cytoplasm
From Acosta, I., et al. (2009) tasselseed1 is a lipoxygenase affecting jasmonic acid signaling in sex determination of
maize. Science 323: 262 – 265. Reprinted with permission from AAAS.
JAR1
conjugation
JA-ILE
JA conjugated to
isoleucine (JA-
ILE) is the active
compound.

177. Jasmonate signaling contributes to
defense against herbivory
WT Mutant without JA
McConn, M., et al. (1997) Jasmonate is essential for insect defense in Arabidopsis. Proc. Natl. Acad. Sci. USA 94: 5473-5477.
When exposed to hungry
fly larvae, plants unable
to produce JA have low
rates of survival.

178. Jasmonates induce the expression
of anti-herbivory chemicals
R.J. Reynolds Tobacco Company Slide Set and R.J. Reynolds Tobacco Company, Bugworld.org
Protease inhibitors
Feeding deterants
Wound-induced signals
Insect oral secretions

179. Jasmonates contribute to systemic
defense responses
Defense
responses are
activated in
distant tissues

180. Jasomonates stimulate production
of volatile signaling compounds
First attack After a while
Herbivore-induced volatiles prime
other tissues (and other plants) for
(indicated in red).
attack making them unpalatable

181. Herbivore-induced volatiles are
recognized by carnivorous and
parasitoid insects
Tim Haye, Universität Kiel, Germany Bugwood.org; R.J. Reynolds Tobacco Company Slide Set and R.J. Reynolds Tobacco Company, Bugworld.org

182. e
JA-induced changes in gene
expression
High JA-Ile
Defense
genes
JA-Ile
Transcription
Proteolysis
Low JA-Ile
JAZ
JA- protein
responsiv
transcription
factor
No
F-box protein transcription
receptor
(COI1)

183. •Response to biotrophic
pathogens
•Induced defense
response
•Systemic acquired
resistance Salicylic Acid
Salicylic acid is named for
the willow Salix whose
analgesic properties were
known long before the
chemical was isolated.
Acetylsalicylic Acid - aspirin
Photo credit: Geaugagrrl
Salicylic Acid – plant hormone and
painkiller

184. Salicylate synthesis is induced upon
attackpathogen
Control +Pathogen
Isochorismate
synthase (ICS) is
induced by pathogen
infection
Reprinted from Métraux, J.P. (2002) Recent breakthroughsin the study of salicylic acid biosynthesis. Trends Plant Sci. 7: 332-334, with permission from Elsevier.
Reprinted by permission from Macmillan Publishers Ltd. Wildermuth, M.C., Dewdney, J., Wu, G., and Ausubel, F.M. (2001). Isochorismate synthase is required to
synthesize salicylic acid for plant defence. Nature 414: 562-565 copyright 2001.
SA accumulation induces PATHOGENESIS
RELATED (PR) and other defense genes

185. Salicylates contribute to systemic
acquired resistance
SAR
SA
MeSA
MeSA SA
SA is necessary in
systemic tissue for
SAR, but the
nature of the
mobile signal(s) is
still up in the air
It is likely that
multiple signals
contribute to SAR
MeSA

186. Plants recognize PAMPS (pathogen-
associated
PAMP-triggered
molecular patterns)
immunity
SA
Immune
Responses
Redrawn from Pieterse, C.M.J, Leon-Reyes, A., Van der Ent, S., and Saskia C M Van Wees, S.C.M. (2009) Nat. Chem. Biol. 5: 308 – 316.
Flagellin is a conserved
bacterial protein recognized
by plants, also known as a
pathogen-associated
molecular pattern (PAMP).
Recognition of PAMPs by a
plant cell triggers a set of
immune responses that are
mediated by salicylic acid.

187. Some pathogens elicit a stronger
defense response
Effector-triggered
immunity
R
SA
Immune
Responses
Redrawn from Pieterse, C.M.J, Leon-Reyes, A., Van der Ent, S., and Saskia C M Van Wees, S.C.M. (2009) Nat. Chem. Biol. 5: 308 – 316.
Many plants express resistance genes that
recognize the effects of bacterial proteins
effector proteins.
The interaction of an R protein with an
effector protein promotes a stronger immune
response, including the hypersensitive
response.

188. The hypersensitive response
involves cell death
Effector-triggered
immunity
R
SA
Pathogen Response (PR) genes
Antimicrobial compounds
Strengthening of plant cell walls
Programmed cell death
Hypersensitive response (HR)
Immune
Responses
From Cawly, J., Cole, A.B., Király, L., Qiu, W., and Schoelz, J.E. (2005) The plant gene CCD1 selectively blocks cell death during the
hypersensitive response to cauliflower mosaic virus infection. MPMI 18: 212-219; Redrawn from Pieterse, C.M.J, Leon-Reyes, A., Van der Ent,
S., and Saskia C M Van Wees, S.C.M. (2009) Nat. Chem. Biol. 5: 308 – 316.

189. The hypersensitive response seals
the pathogen in a tomb of dead cells
Drawing credit Credit: Nicolle Rager Fuller, National Science Foundation; Photo reprinted by permission of Macmillan Publishers Ltd. Pruitt,
R.E., Bowman, J.L., and Grossniklaus, U. (2003) Plant genetics: a decade of integration. Nat. Genet. 33: 294 – 304.
The HR kills the infected cells and
cells surrounding them and prevents
the pathogen from spreading.
HR
No HR
Without a hypersensitive
response, the pathogen
can multiply.

190. Other hormones affect defense
response signaling
Reprinted from Robert-Seilaniantz, A., Navarro, L., Bari, R., and Jones, J.D.G. (2007). Pathological hormone imbalances. Curr. Opin. Plant Biol. 10: 372– 379.
with permission from Elsevier.
As part of their immune
responses, plants
modulate synthesis and
response to other
hormones. Some
pathogens exploit the
connections between
growth hormones and
pathogen-response
hormones to their own
advantage, by producing
“phytohormones” or
interfering with hormone
signaling.

191. Hormonal signaling is critical for plant
defenses against abiotic and biotic stresses.
ABA and ethylene are produced in stressed
plants and critical for activating their defense
pathways.
JA and SA contribute to local and systemic
defenses against pathogens.
Understanding plant hormonal responses to
stress is needed to improving agricultural
yields. Abiotic and biotic stresses are major
causes of crop losses and reduced yields
and which must be minimized.
Summary – stress responses

192. Crosstalk (or cross-regulation) occurs when two
pathways are not independent. It can be positive
and additive or synergistic, or negative.
H1 H2
Response
H1 H2H1
Response
Crosstalk between hormone
signaling pathways

193. and additive or synergistic, or negative.
Crosstalk (or cross-regulation) occurs when two
pathways are not independent. It can be positive
Crosstalk can affect the
synthesis, transport or
signaling pathway of another
hormone.
H1 H2
Response
H1 H2H1
Response
H2 H1 H2
Response
Crosstalk between hormone
signaling pathways

194. Synergistic requirement for JA and
responseET signaling in defense
a TF that induces
JA
and ERF1 ERF1
ET Defense
genes
JA and ET signaling are
both required for high-
level expression of ERF1,
defense gene expression
NO JA NO ET
response response

195. Negative
SA
interaction between JA and
in defense responses
Why does ABA reduce SA and JA
signaling? Perhaps a plant that is
already stressed and producing high
levels of ABA may be better off
temporarily restricting its responses to
pathogens.
In defense signaling,
the JA and SA
pathways are mutually
antagonistic (locally),
and both are
antagonized by ABA.

196. GA and
with
DELLAs interact extensively
other signaling pathways
Although it is clear that GA’s effects
on DELLA proteins are very
important, we don’t yet understand
what these proteins do.
Just about every stage of the
plants life is coordinated by GA
and its effects on the other
hormone signaling pathways.

197. GA and
with
DELLAs interact extensively
other signaling pathways

198. Hormones coordinate plant growth and defense
Many aspects of hormone synthesis, homeostasis and
signaling are still being discovered
Knowledge of these processes provides tremendous
opportunities for agricultural improvements including the
development of stress-resistant and pathogen-resistant
plants, plants with greater abilities to take up nutrients,
foods that stay fresh longer, and increased crop yields
Ongoing research

199. The field of plant hormones is
blossoming and fruitful