Download Chapter 39 Student Notes Plant Responses to Internal External

Chapter 39 Student Notes
Plant Responses to Internal External Signals
Concept 39.1: Signal transduction pathways
• Plants have cellular receptors that detect changes in their
• For a stimulus to elicit a response, certain cells must have an appropriate
receptor
• Stimulation of the receptor initiates a specific signal transduction pathway
• These are morphological adaptations for growing in darkness, collectively
called
• After exposure to light, a potato undergoes changes called
, in which shoots and roots grow normally
• A potato’s response to light is an example of cell-signal processing
• The stages are reception, transduction, and response
•
Internal and external signals are detected by receptors, proteins that change
in response to specific stimuli
•
.
transfer and amplify signals from receptors to proteins
that cause responses
•
Cellular response is primarily accomplished by two mechanisms:
(1)
(2)
Concept 39.2: Plant Hormones
A.
are defined as chemical messengers that coordinate different
parts of a multicellular organism
• They are produced by one part of the body and transported to
another
B. A
is a plant growth response from hormones that results in the
plant growing either
(positive) or
(negative) from a
stimulus
•
is the growth of a shoot in a certain
direction in response to light.
• Positive phototropism is the growth of a plant toward
•
Negative phototropism is the growth of a plant
from light
C. Discovery of
1. Charles and Francis Darwin (1881)
Concluded that
tips were responsible for
sensing light and producing a substance that was transported
to
region
2. Peter Boysen-Jensen
• Demonstrated that the substance for
was
mobile
3. F. W. Went (1926)
• Named substance for elongation—
A Survey of Plant Hormones
• In general, hormones control plant growth and development by
affecting the
,
, and
of cells
• Plant hormones are produced in very low concentration, but a minute
amount can greatly affect
and
of a
plant organ
•
D. Actions of Plant Hormones
1. Six Classes of Plant Hormones:
a.
(natural auxin—IAA–indoleacetic acid)
• Stimulates cell elongation
• Promotes
formation
• Regulates
development
• Enhances
dominance
b.
• regulate cell division
• Anti-aging effects (keeps cut flowers fresh)
• Slow
c.
• Promote stem
• Promote seed germination
• Contributes to fruit growth
d.
• Promote
and
• Promotes xylem differentiation
• Slow leaf abscission
e.
• Promotes seed dormancy until optimum conditions
•
tolerance (closes stomata during
water stress)
f.
(
)
• Promotes fruit
• Prepare for leaf abscission
• Initiates triple response (growth maneuver so a shoot
can avoid an obstacle)
Concept 39.3: Plant Responses to Light
A.
is the term used to describe the effects of light on plant
morphology
B. There are two major classes of light receptors:
1.
initiate a number of plant responses to
light including phototropisms and the light-induced opening of the
stomata
2.
are pigments that regulate many of a plant’s responses
to light throughout its life
• Responses include seed
and
• Phytochromes exist in two
states, with
conversion of Pr to Pfr triggering many developmental responses
•
absorb mostly red light
Biological Clocks and Circadian Rhythms
• Many plant processes
during the day
• Many legumes lower their leaves in the evening and raise them in the
morning, even when kept under constant light or dark conditions
C.
are physiological cycles that have a frequency of
about 24 hours and that are not paced by a known environmental clock.
In plants, the surge of Pfr at dawn resets the biological clock.
The combination of a phytochrome system and a biological clock allow
the plant to accurately assess the amount of daylight or darkness and
hence the time of the year
D.
is defined as a physiological response to a
photoperiod (the relative lengths of night and day).
•
•
Important in plant life cycles such as
It is
length—not day length—that controls flowering
and certain other response to photoperiod.
•
plants require a period of continuous darkness
longer than a critical period (length of day) in order to flower. These
plants usually flower in late summer, fall, and winter
•
flower only if a period of continuous darkness was
shorter than a critical period. They often flower in late spring or early
summer. They are actually short-night plants.
•
plants can flower in days of any length.
E. Responses to Other Environmental Stimuli
•
•
1.
•
•
•
2.
•
is a plant’s response to gravity
show positive gravitropism
show negative gravitropism
play a key role in gravitropism
is directional growth as a response to touch
Ex: tendrils
Environmental Stresses
• Environmental stresses have a potentially adverse effect on
,
, and
• Stresses can be
(nonliving) or
(living)
• Abiotic stresses include drought, flooding, salt stress, heat stress, and cold
stress
Concept 39.5: Plants respond to attacks by
and
• Plants use defense systems to deter herbivory, prevent infection, and combat
pathogens
Defenses Against
• defenses such as
and chemical defenses such as
or
• Some plants even “recruit” predatory animals that help defend against
specific
Defenses Against Pathogens
• A plant’s first line of defense against infection is the
and
If a pathogen penetrates the dermal tissue, the second line of defense is a
that kills the pathogen and prevents its spread
• A
pathogen is one that a plant has little specific defense
against
• An
pathogen is one that may harm but does not kill the host
plant
The Hypersensitive Response
• The
– Causes cell and tissue death near the infection site
– Induces production proteins, which attack the pathogen
– Stimulates changes in the cell wall that confine the pathogen
•