Plant Regulators Flashcards
- a photoreceptor that absorbs light and helps plants
sense changes in light quality and duration.
Phytochrome
Two forms of phytochromes
Pr;
Pfr
Pr - absorbs _light with peak wavelength of __
red;
660nm
the inactive phytochrome form and does not initiate photomorphogenic response
Pr
Pfr - absorbs ____ light around ___nm
far-red;
700 to 750 nm
the active form and initiates responses such as seed germination.
flowering, and other growth processes
converts back to Pr after absorbing far-red light
Pfr
- refers to plant growth influenced by light; changes in shape, structure, and function
Photomorphogenesis
Photomorphogenesis:
seedlings undergo ___through ____where plant stems
grow even in dark environments to quickly reach potential light source
etiolation;
skotomorphogenesis
Two stages of photomorphogenesis
Pattern Specification;
Pattern Realization
- preparation of cells and tissues to
become more responsive to light
Pattern Specification
- occurs when the actual light-inducted
responses are executed
Pattern Realization
Photomorphogenic responses: 4
- Leaf expansion
- Stem shortening and thickening
- Flowering timing - via photoperiodism
- Shade avoidance
- the physiological response of plants to the length of day and night,
influencing seasonal behaviors such as flowering, seed
germination, and dormancy
Photoperiodism
refers to how plants use the length of day and night to determine the timing of
their flowering.
Photoperiodism in Flowering
Internal clocks which measures the specific length of darkness that a plant needs to start or prevent flowering
Critical night length
Types of Photoperiodic Plants:
Short-Day plants
Long-Day plants
Day-neutral plants
- plants which require less exposure to light; need nights longer than their critical night length to flower.
Short-Day plants
- plants which require more exposure to light
need nights shorter than their critical night length to flower.
Long-Day plants
- plants that are not sensitive to day length
Day-neutral plants
movement in plants is mostly seen as
__, __, __, or as__ of
plant parts
bending, turning, twisting or as elongation
movement of plants can be divided into:
Tropic Movements
Nastic Movement
Growth movements which occur in the direction of the stimulus; may be towards or away from the stimulus
tropic movement
Tropic movements are of various types (6)
Phototropism:
Chemotropism:
Hydrotropism:
Geotropism:
Thigmotropism:
Thermotropism:
Stimulus: Light
Description: This is the growth response of plants toward or away from
light.
Phototropism
___ is when a plant grows toward light (e.g., plant
stems and leaves), and __ is when a plant grows away
from light (e.g., roots).
Positive phototropism;
negative phototropism
In ___phototropism, plant cells on the __ side
elongate more than those on the ___ side, causing the plant to bend toward the light source. The hormone __plays a critical role in this
process.
positive;
shaded;
light-exposed;
auxin
Stimulus: Chemicals
Description: is the growth or movement of a plant part in response to chemicals.
Chemotropism
Pollen tube growth towards the ovule during fertilization, roots
growing toward nutrients like nitrogen, or avoidance of toxic substances is an example of
Chemotropism
Stimulus: Water
Description: refers to the plant’s growth in response to water
Hydrotropism
Roots exhibit ___ by
growing toward areas of higher moisture content in the soil to
optimize water uptake.
positive hydrotropism
Stimulus: Gravity
Description: is the directional growth of plant parts in
response to gravity.
Geotropism
____ is the growth of roots downward
(toward gravity), while ___ is the growth of stems and
shoots upward (away from gravity).
Positive geotropism;
negative geotropism
Geotropism response involves the plant’s gravity-sensing cells
(___) that detect the direction of gravity and help orient growth
accordingly
statocytes
Stimulus: Touch
Description: is the response of plants to physical contact or
touch
Thigmotropism
___ is exhibited by climbing plants or vines that
wrap around supports (e.g., tendrils or stems of climbing plants)
Positive thigmotropism
Stimulus: Temperature
Description: is the growth response of plants to temperature
gradients. It involves movement or growth toward warmer or cooler areas.
Thermotropism
These movements are non-directional responses to the stimuli;
independent of the direction of the stimulus; due to changes in
turgor or growth.
Nastic Movements
Types of Nastic movement (4)
Photonasty
Nyctinasty
Thermonasty
Seismonasty or Thigmonasty
Stimulus: Light
Description: is the nastic movement of plant parts in response
to light, but the movement is not necessarily towards or away from the light
source (like in phototropism).
Photonasty
It often involves the opening or closing of
flowers or leaves in response to changes in light intensity.
Photonasty
Stimulus: Darkness (or changes in the light cycle)
Description: is the movement of plant parts in response to
the onset of darkness or changes in the photoperiod (day-night
cycle).
Nyctinasty
often seen in flowers or leaves that open during the day and close at night
Nyctinasty
Stimulus: Temperature
Description: is the response of plants to temperature changes.
This can involve the opening or closing of flowers, leaves, or other plant
structures in response to temperature variations.
Thermonasty
Stimulus: Mechanical stimulus (touch or vibration)
Description: , is the movement of plant parts
in response to mechanical stimuli such as touch, vibration, or even
shaking. This is typically a rapid, non-directional response to external
physical disturbances.
Seismonasty, or thigmonasty
Environmental and Genetic Factors on control of flowering:
Influence of light, temperature, and plant genetics
: The duration of light and dark periods affects flowering
Photoperiodism
: these plants Flower when daylight exceeds a critical length (e.g., __ and ___).
Long-Day Plants;
spinach, lettuce
these plants Flower when daylight is shorter than a critical length (e.g., __ and ___)
Short-Day Plants;
chrysanthemums,
poinsettias
these plants Flowering is not affected by day length (e.g., __ and __)
Day-Neutral Plants;
tomatoes, corn
Environmental and Genetic Factors: Influence of Temperature (2)
Vernalization;
Thermoperiodism
: Some plants require a period of cold temperature to flower (e.g., winter wheat,
biennial plants like carrots)
Vernalization;
: Daily temperature fluctuations can influence flowering, with some plants
requiring specific day/night temperature patterns
Thermoperiodism
Environmental and Genetic Factors: Influence of plant genetics (2)
Genetic Regulation;
Genetic Mutations
Flowering genes control the transition from vegetative to reproductive growth.
Genetic Regulation:
Key flowering genes (4)
FLOWERING LOCUS T (FT):
CONSTANS (CO):
LEAFY (LFY):;
APETALA1 (AP1):
Genetic mutations can alter flowering __ and __s, impacting
the adaptability and reproduction of plants
time and pattern
is a hypothetical hormone or signal produced in leaves under favorable
conditions, inducing flowering
Florigen
Florigen Moves from the __to the___ where it triggers floral development.
leaves ;
shoot apical meristem
In many plants, the ___ has been identified as a component of
florigen.
FT protein
Acts as a mobile signal promoting flowering.
FLOWERING LOCUS T (FT):
: Regulates FT expression in response to photoperiod.
CONSTANS (CO)
Integrates signals and promotes floral meristem identity
LEAFY (LFY):
Initiates flower development and determines floral organ identity
APETALA1 (AP1):
Influence of External Cues (2)
Light (Photoperiod);
Temperature (Thermoperiod)
:
Plants perceive changes in day
length through photoreceptors
like phytochromes and
cryptochromes.
Photoperiodic Response
: CO
protein levels and activity are regulated by __, influencing FT
expression and thus flowering.
Signal Transduction; light
High or low
temperatures can accelerate or delay
flowering
Temperature Sensitivity:
: Extended exposure to cold
temperatures leads to changes in gene
expression that promote flowering once
favorable conditions return.
Vernalization
High temperatures can
negatively impact flowering and fruit set,
particularly in sensitive crops.
Heat Stress:
is the process by which prolonged exposure to cold
temperatures induces flowering in some plants
Vernalization
Flowering Pathways (3)
Vernalization
Photoperiodism
Autonomous pathways
Cold temperatures promote the expression of flowering genes
(e.g., ____ in wheat) while repressing flowering
inhibitors (e.g., ____ in Arabidopsis).
VERNALIZATION1 (VRN1);
FLOWERING LOCUS C (FLC)
is the response of plants to the relative lengths of light and dark periods,
influencing flowering.
Photoperiodism
: Require longer daylight periods to flower. The CONSTANS (CO) gene
promotes the expression of FT under long-day conditions.
Long-Day Plants
Flower when the day length is shorter. The CO gene’s activity is inhibited
during long days, preventing FT expression.
Short-Day Plants:
control flowering based on internal developmental cues,
independent of external environmental factors.
Autonomous pathways
pathway involves the regulation of flowering genes by the plant’s
developmental state and internal signals
Autonomous pathways
Integration of Signals (4)
Signal Convergence;
Gene Interaction:
Hormonal Regulation
Environmental Cues:
Flowering is controlled by the integration of multiple pathways
(vernalization, photoperiodic, autonomous) to ensure optimal timing.
Signal Convergence:
Key regulatory genes (e.g., FT, CO, FLC) interact to integrate
signals from different pathways
Gene Interaction:
Hormones such as ___ can interact with flowering
pathways to modulate the timing and development of flowers
Hormonal Regulation: ;
gibberellins
External factors like light, temperature, and nutrient availability
provide additional layers of regulation to fine-tune the flowering process
Environmental Cues:
Before death, plants undergo deteriorative processes that end
their functional life, known as ___.
senescence
The death of a plant or plant
parts as a direct consequence of senescence
Programmed Cell Death (PCD):
types of senescence
Overall Senescence;
Top Senescence;
Deciduous Senescence;
Progressive Senescence
Description: Occurs in annual plants, where the entire plant undergoes
aging and eventually dies.;
Process: Triggered after flowering and seed production; the whole
plant begins a rapid decline, leading to death
Overall Senescence
Description: Observed in perennials; senescence affects only
the parts above ground.
Characteristics: Roots remain alive and viable, allowing for
regrowth in the following season
Top Senescence
Description: Occurs in woody plants; less drastic as it mainly affects
leaves.
Characteristics: All leaves age and shed, typically in the fall,
allowing the plant to conserve energy and resources during
unfavorable seasons
Deciduous Senescence
Description: A gradual process seen in plants where leaf senescence
progresses from the base upwards as the plant grows.
Characteristics: This pattern allows the plant to redistribute nutrients
from older leaves to new growth
Progressive Senescence
Importance of Senescence in Plants
Resource Redistribution:
Adaptation and Survival:
Hormonal Regulation
Controlled by hormones like __ and ___, which signal the onset of senescence.
ethylene and
abscisic acid
Biochemical Changes During Ripening:
Color change, softening, and sweetness increase
Color Change (2)
Softening: (2)
Sweetness Increase (2)
Color Change: Chlorophyll Degradation, Carotenoids and Anthocyanins
Softening: Cell Wall Breakdown, Water Movement
Sweetness Increase: Starch Conversion, Acid Reduction
As fruits ripen, the green pigment chlorophyll breaks down
Chlorophyll Degradation:
These
pigments become more
prominent, resulting in yellow,
orange, and red hues in the
fruit
Carotenoids and
Anthocyanins:
Cell Wall Breakdown:
Enzymes like __ and __break down the cell wall components, leading to softer texture
pectinases and cellulases
as the key hormone in fruit ripening, along with other hormones that influence the process.
Ethylene
Ethylene triggers a cascade
of biochemical events, including __, __, and ___
enzyme activation
for cell wall breakdown, chlorophyll degradation,
and starch conversion
is often used to
artificially induce ripening in harvested fruits
Ethylene gas
: Help in maintaining fruit firmness and delaying
ripening until the fruit is ready
Auxins
: Influence the size and quality of the fruit,
and may delay ripening in some cases
Gibberellins
Plays a role in the onset of fruit
ripening and senescence, contributing to color change
and sugar accumulation.
Abscisic Acid (ABA):
A natural process by which a plan intentionally sheds parts of itself, such as
leaves, flowers, fruits, or seeds due to developmental or environmental signals
abscission
Purpose of Abscission (3)
Seasonal Leaf Drop ;
Fruit and seed Release;
Defense mechanism
Phases of Abscission:
___ - Leaf is healthy and auxin
gradient flows from leaf blade to stem
Phase I
Phases of Abscission:
- auxin gradient is reversed
or reduced causing cells in the zone
of abscission to react to ethylene
Phase II
Phases of Abscission:
- hydrolytic enzymes break
down cell walls and plant organ
detache
Phase III
