Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 36
Plant Growth and
Development
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Plant growth and development are
controlled by
• Internal factors like location of cell in
plant body
–Causes some genes in cell to be turned
off and others to be turned on, thus
affecting gene expression during
development
• Environmental factors like changing
day length
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Germination and
seedling growth
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Germination is the process of seed
sprouting
• Internal factors affecting germination
–Maturity of the embryo
–Presence or absence of chemical
inhibitors
–Presence or absence of hard, thick
seed coats
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Germination, cont.
• External environmental factors
affecting germination include
requirements for
–Oxygen
–Water
–Temperature
–Light
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Photoperiodism is any response
of plants to the duration and
timing of light and dark
• In many plants, flowering is a
photoperiodic response
–Short-day plants
–Long-day plants
–Intermediate-day plants
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Light
treatment
Photoperiodic
responses
of shortday and
long-day
plants
Short-day
plant
Long-day
plant
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Photoperiodism, cont.
• Day neutral plants
–Flowering is not affected by
photoperiod
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Phytochrome is
• The photoreceptor in photoperiodism
• A family of ca. 5 blue-green pigments
• Each type has two forms named by the
wavelength of light they absorb
–Pr
–Pfr
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Phytochrome, cont.
• Pfr is the active form, triggering
or inhibiting physiological
responses such as
–Flowering
–Shade avoidance
–A light requirement for germination
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Phytochrome
This pigment
occurs in two forms,
Pr and Pfr, and readily converts
from one to the other.
Red light (660 nm) converts Pr to Pfr,
and far-red light (730 nm) converts
Pfr to Pr
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Phytochrome, cont.
• Each type of phytochrome may
have physiological functions both
–Unique and
–Overlapping
• PhyB seems to exert its influence
at all stages of the plant life cycle
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Phytochrome-induced
responses
• Some are rapid and short-term
–E.g., changes in membrane
properties
• Others are slower and long term
–E.g., regulation of gene
transcription
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Absorption of light by
phytochrome
• Triggers one or more signal
transduction pathways
–In signal transduction, a receptor
converts an extracellular signal into
an intracellular signal that causes
some change in the cell
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Phytochrome signal transduction
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Circadian rhythm
• A regular period in the growth or
activities of a plant or organism
–That approximates the 24-hour day
–Is reset by the rising and setting of
the sun
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Circadian rhythm, cont.
• Examples are
–The opening and closing of stomata
–Sleep movements
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Phytochrome and cryptochrome
• Photoreceptors that sometimes
interact to regulate similar
responses
–Phytochrome strongly absorbs red
light
–Cryptochrome absorbs blue light
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Plant movements occurring in
response to external stimuli
• Nastic movements
–Temporary and reversible
–Direction of movement is
independent of the direction of the
stimulus
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Nastic
movements
Mimosa pudica:
Leaves photographed
before being touched
(above) and
several seconds after
being touched (below)
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Biology, Seventh Edition
Nastic movements
Pulvini are
located in
three areas
—at the base
of each leaflet,
at the
base of
each cluster of
leaflets, and at the base of each leaf; Only changes
in the pulvini at the base of leaflets
are shown
Copyright © 2005 Brooks/Cole — Thomson Learning
CHAPTER 36 Plant Growth and Development
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Plant movements occurring in
response to external stimuli, cont.
• Tropisms
–Directional growth responses (i.e., the
direction of growth is dependent on
the direction of the stimulus)
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Phototropism
• Response to the direction of light
• Gravitropism
• Response to gravity
• Thigmotropism
• Response to contact with a solid object
• Heliotropism
• Ability of leaves or flowers to track the sun
across the sky
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Gravitropism
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Heliotropism
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Plants produce and respond to
hormones that
• Act as highly specific chemical
signals
• Elicit a variety of responses that
regulate
–Growth
–Development
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Hormones
• Are effective in very small
concentrations
• Functions of some overlap
• Many physiological activities are
regulated by interactions of
several at once
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
General
mechanism
of action of
plant
hormones
I
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Plant hormones bind to specific
receptor proteins in or on target
cells
• Binding may trigger production of
a second messenger (e.g., Ca2+)
–Second messenger may bind to and
activate or inactivate certain
enzymes
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Plant hormone binding, cont.
• Activation or inactivation of
enzymes may lead to either or
both
–Altered membrane permeability
–Altered gene expression
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Hormones affecting plant
growth and development
• Auxin is involved in
–Cell elongation
–Tropisms
–Apical dominance
–Inhibition of axillary buds by the
apical meristem
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Isolating auxin from coleoptiles
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Hormones, cont.
• Auxin, cont.
–Fruit development
–Stimulating root development on
stem cuttings
• Some synthetic auxins (2,4-D
and 2,4,5-T) are selective
herbicides
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Phototropism and the
unequal distribution of
auxin
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Hormones, cont.
• Gibberellins are involved in
–Stem elongation
–Flowering
–Germination
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Gibberellin and
stem elongation
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Hormones, cont.
• Cytokinins
–Promote cell division and
differentiation
–Delay senescence
–Interact with auxin and ethylene in
apical dominance
–Induce cell division in tissue culture
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Auxincytokinin
interactions
in tissue
culture
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Hormones, cont.
• Ethylene plays a role in
–Ripening fruits
–Apical dominance
–Leaf abscission
–Wound response
–Thigmomorphogenesis
–Senescence
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Hormones, cont.
• Abscisic acid is an environmental
stress hormone involved in
stomatal closure caused both
–By water stress
–In seed dormancy
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Abscisic
acid and
seed
germination
Arrows show
where some of the
kernels have
germinated while
still on the ear,
producing roots
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Brassinolides are
• Plant steroids
• Probably involved in aspects of
plant growth and development
such as
–Cell division
–Cell elongation
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Salicylic acid
• Helps defend plants against
–Pathogens
–Insect pests
• May bind to a cell receptor to
switch on genes to
–Fight infection
–Promote wound healing
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Salicylic acid, cont.
• A volatile form of it may serve as
an airborne chemical signal from
virus-infected plants to healthy
ones
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Systemin
• Is a plant polypeptide with
hormonal properties
• Stimulates a natural defense
mechanism in which
–Plant produces protease inhibitors
to disrupt insect digestion
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Oligosaccharins
• Are short, branched chains of
sugar molecules
• Have various functions
–Inhibit flowering
–Stimulate vegetative growth
• Bind to membrane receptors and
alter gene expression
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Jasmonates
• Affect several plant processes like
–Pollen development
–Root growth
–Fruit ripening
–Senescence
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Biology, Seventh Edition
CHAPTER 36 Plant Growth and Development
• Jasmonates, cont.
• Are produced in response to the
presence of
–Insect pests
–Disease-causing organisms
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