Ro 1 Flashcards
____ is the process where an extracellular signal activates a receptor, triggering a cascade of intracellular events that lead to a specific cellular response (e.g., altered metabolism, gene expression, or cell division).
signal transduction
signal transduction cannot be amplified at any step, true or false
false, it can be amplified at any step
Two Major Types of Mutations:
Hyposensitive (Insensitive)
Hypersensitive (Constitutive)
What is Hyposensitive (Insensitive) Mutation:
Reduced response to signals due to receptor or pathway defects.
signal –> no response (strong signal turns weak and leads to no response)
What is Hypersensitive (Constitutive) mutation:
Overactive pathways even in the absence of signals.
No signal –> response
what’s the general pathway for signal transduction:
stimuli - receptor - pathway - transmission (transport) - response
Plants use chemical messengers ____ to coordinate growth, development, and environmental responses. What are these messengers?
hormones
6 major plant hormones:
Auxin (IAA), Cytokinin, Gibberellin (GA), Ethylene, Abscisic Acid (ABA), Brassinosteroids
3 minor plant hormones
strigolactone, jasmonic acid, salicyclic acid
____ means “to grow”
auxin
The first notion of auxin came from ____ experiments
Darwin’s phototropism
how do auxin’s (IAA) function
Promotes cell elongation, apical dominance, and root formation.
auxin is considered as “____” in plants
Morphogen
IAA regulates ____ (growth toward light) and ____ (growth relative to gravity).
phototropism and gravitropism
what are auxins
a plant hormone which causes the elongation of cells in shoots and is involved in regulating plant growth.
what is the most active and abundant auxin
IAA
A series of experiments for ____light phototropism proved the presence of chemical substance regulating cell growth
blue
what is apical dominance
when lateral bud growth is inhibited. So the apex bud releases auxins that stop the lower plant stems from growing out laterally. When the apex bud is cut, then the lateral buds grow out and you have bushier plants
____ growths should be responsible for the tropism. (symmetrical or asymmetrical)
asymmetrical
how do auxins work, in terms of recpetors or repressors
auxin binds to TIR1, a subunit of the SCF complex, IAA proteins are degraded, TFs or ARFs are activated for growth-related genes
cytokinin involves ____ division
cell division
New cells are supplied from ____ cells
meristem
Once a cell is differentiated for a specific function at a specific position, this
differentiated cell lose ____. However, in certain cases such as
wounding, cells gain a capacity to ____ a couple of more times to heal the
wounding. Then the cells at the wounding site undergo differentiation to
specific cells (____) and stop cell division
its capability to divide because they shift their focus to performing specific tasks
divide (dedifferentiation)
protective cork cells (redifferentiation), once wound is sealed, cork cells stop dividing
why are protective cork cells formed?
Plants lack a mobile immune system, so they rely on local cellular responses like dedifferentiation and redifferentiation to repair damage.
The Austrian scientist, Gottlieb Haberlandt, proposed a ____ chemical substance, which can promote plant cell division, based on his experiment using ____ tissue experiments
water soluble, vascular
Two streams of research resulted in the identification of a chemical substance for cell division:
screening natural or synthetic compounds for cell division (purification)
studies of the crown gall forming bacteria (molecular genetics, biochem)
____ discovered that ____ contains an unidentified substance that supports continuous cell division in mature, differentiated cells. Despite its efficacy, this substance could not be purified.
Philip White, coconut milk
Skoog found that aged or autoclaved ____ DNA exhibits potent cell-division-promoting activity.
This substance was purified, identified as an adenine derivative, and named ____.
____ is not a natural plant product but a by-product of the ____ of DNA.
This discovery influenced the development of the Murashige and Skoog (MS) medium, widely used in plant tissue culture.
herring sperm, kinetin, kinetin, heat induced degradation
Letham isolated a **natural **cell-division-promoting substance, ____, from immature maize endosperm.
Zeatin is an adenine derivative with an ____ side chain and is now recognized as the ____ in plants.
It is synthesized in chloroplasts from ____ and ____ (dimethylallyl diphosphate) through the action of the enzyme isopentenyl transferase (____).
zeatin, isoprene, dominant cytokinin, ATP, DMAPP, IPT
Cytokinin-like compounds produced by bacteria and fungi can cause abnormal growth patterns, such as ____.
fasciation
what does fasciation look like
perpendicular growth relative to main stem, 2 flowers smushed together, flattened stems, flower heads that look like compressed stems together
what delays senescence (aging) in leaves.
cytokinins
Agrobacterium tumefaciens infects plants through wounded tissues where it can enter and interact with the plant cells.
The bacterium transforms infected plant cells into tumor-like tissue, known as a ____, which is an unorganized, ____ mass of dividing cells.
These cells lose the usual regulatory controls on growth and division, continuing to divide throughout the plant’s lifecycle.
gall, undifferentiated
Heating the gall tissue to 42°C kills A. tumefaciens without harming the plant cells. The bacteria-free gall tissue retains the capacity to ____, forming undifferentiated callus tissue in a hormone-free culture medium.
Significance:
The ability of plant cells to grow uncontrollably after bacterial removal hints at a permanent transformation of the plant genome, drawing parallels to cancer in animals, where cells grow uncontrollably.
divide indefinitely
Ti Plasmid (Tumor-Inducing Plasmid):
A key component in A. tumefaciens that carries genes responsible for gall formation.
Contains ____ which integrates into the plant cell genome and hijacks its machinery.
Genes Encoded on T-DNA:
____, a plant hormone, is synthesized from tryptophan, promoting excessive cell growth.
____, produced by bacterial enzymes, promote uncontrolled cell division.
____ is a unique molecule synthesized from arginine and alanine, serving as a nutrient source exclusively for A. tumefaciens.
T-DNA, auxin, cytokinins, octopine
High cytokinin:low auxin ratio → ____ formation.
Low cytokinin: high auxin ratio → ____ formation.
long shoot, long root
“____” Disease:
Observed in ____ plants, where infected plants grew abnormally ____, causing ____ seed production.
In the 1930s, Japanese scientists identified the pathogen as the fungus Gibberella fujikuroi
Foolish Seedling, rice, tall, reduced
Gibberellin Purification
In the 1950s, UK and US scientists purified a compound from Gibberella cultures and named it gibberellic acid.
Simultaneously, Japanese researchers purified three related compounds, naming them GA1, GA2, and GA3.
____ was found to be identical to the UK/US’s gibberellic acid, establishing it as one of the most bioactive forms. (which GA)
GA3
Researchers confirmed that plants ____ produce gibberellins (naturally or synthetically). These hormones are synthesized in multiple cellular locations: (3 locations)
naturally
Chloroplasts.
Endoplasmic Reticulum (ER).
Cytosol.
Gibberellins belong to the ____ (or isoprenoid) family.
terpenoid
Gibberellins played a key role in the ____ (1940-1960):
Scientists used dwarf varieties of crops (which are more resistant to lodging, or falling over).
Gibberellins’ role in manipulating plant growth contributed to higher yields and the development of modern agriculture.
Green Revolution
Seedlessness in grapes arises from a genetic defect that causes early seed abortion after fertilization. This defect ____ impacts berry size. (size)
negatively (smaller)
Treating seedless grapes with gibberellins ____ berry size and ____ fruit stalks (pedicels). (length shorter or longer?)
GAs compensate for the absence of seeds, which typically promote fruit growth through hormonal signaling.
increases, elongates
Mechanisms Behind Seedless Fruit Formation
____ :
Fruit develops without fertilization, e.g., bananas and some citrus fruits.
Parthenocarpy
Mechanisms Behind Seedless Fruit Formation
____:
Pollination and fertilization occur, but seeds abort early in development, as in seedless grapes.
Gibberellins stimulate cell expansion and division in the fruit, improving size and quality despite aborted seeds.
Stenospermocarpy
Defoliation Observed (1901):
Street lamps fueled by ____ caused trees nearby to lose leaves. A Russian graduate student identified ____ as the active compound in coal gas responsible for this effect.
coal gas, ethylene
It was noted that ____ emit a gaseous substance that accelerates the ripening of nearby immature fruits.
ripened fruits
____ was identified as a natural product synthesized by plants. Synthetic ethylene and its analogs were found to induce dramatic physiological changes in plants, particularly ____ and leaf abscission.
ethylene, fruit ripening
Climacteric Fruits:
Show a rise in ____ and a spike in ____ production before ripening.
Ethylene has an autocatalytic effect, meaning it ____, creating a positive feedback loop that accelerates ripening.
Examples: ____, ____, mangoes, peaches, and ____. (think of fruits you have at home and see ripening)
respiration, ethylene, promotes its own production, apples, bananas, tomatoes
Non-Climacteric Fruits:
____ respiratory or ethylene production changes during ripening. (how do they compare to climacteric fruits)
____ sensitive to externally applied ethylene, making ripening control ____.
Examples: Citrus, ____, cherries.
do not exhibit the same, less, more difficult, grapes
Applications for ethylene, how is ethylene used in real life?
used to regulate the ripening process, reducing losses from spoilage
trigger uniform ripeneing
inhibitors prevent or delay ripening for storage
The biosynthesis of ethylene involves the Yang Cycle, where ____ is converted into ____ and then to ____. This process is tightly regulated and highly active in climacteric fruits during ripening.
methionine -> ACC -> ethylene
Non-climacteric fruits, like grapes and citrus, do not rely on ethylene for ripening.
Their ripening mechanisms are less understood, and controlling their post-harvest ripening remains a challenge.
For example, the trigger for ____ (the onset of ripening in grapes) is still unknown, complicating their management.
veraison
Enzymes that add phosphate groups to target molecules (phosphorylation) are ____
kinases
Enzymes that remove phosphate groups (dephosphorylation), reversing the effect of kinases are ____
phosphatases
Sequential phosphorylation events are known as ____, such as the MAP kinase cascade:
____ activates ____, which in turn activates MAPK.
These cascades amplify the signal, allowing small stimuli to trigger a significant cellular response.
kinase cascades, MAPKKK, MAPKK
4 main differences between plant and animal signal transduction
GCPRs aren’t important in plant transduction
plant transduction evolved from prokaryotic and eukaryotic ancestors
signals are sensed at multiple subcellular sites in plants
depresiion is common in plant transduction
No functional GPCRs have been identified in ____, except for one heterotrimeric G-protein encoded in the ____ genome.
Plant signaling evolved differently, incorporating mechanisms inherited from both eukaryotic and prokaryotic ancestors.
plants, arabidopsis
Plants have ____ Systems:
Inherited from prokaryotes, these systems involve a ____ protein and a ____ protein.
Examples in plants include pathways involving: (2 examples)
two-component, sensor and response
cytokinin signalling, ethylene signalling
____, derived from prokaryotic ancestors, contribute signaling mechanisms like those involving ____ (blue-light photoreceptor).
chloroplasts, cyrptochrome (blue-light recpetors)
Unlike animals, plants can sense signals at multiple subcellular locations:
Brassinosteroids: Plasma membrane.
Cytokinin: Plasma membrane.
Red light: ____
Blue light:
Plasma membrane (involving ____).
Nucleus (involving ____).
Chloroplast thylakoid membrane (Zeaxanthin).
____: Endoplasmic reticulum.
____: Nucleus (via SCFTIR1 complex).
cytosol, ethylene, photoropin, cryptochrome, auxins
Plants often regulate signals through de-repression, which involves: 2 things
repressor protein inactivation, ubiquination
Ubiquitination tags proteins for degradation by the ____ proteasome.
26s
Ubiquitin:
A small ____ protein (8.5 kDa) found in all eukaryotic cells.
It tags specific proteins for ____ or other cellular processes, acting as a molecular “marker.”
Ubiquitin is encoded by ____ genes in humans.
Ubiquitination Process:
A sequence of enzymatic steps that ____, leading to their degradation by the 26S proteasome or modulation of their activity.
regulatory, degradation, 4
tags proteins with ubiquitin for degradation, acts as molecular marker
Ubiquitin-____ Enzyme (E1):
Activates ubiquitin by loading it onto itself.
This step requires ____.
Ubiquitin-____ Enzyme (E2):
Accepts ubiquitin from the E1 enzyme and transfers it to a ____ protein.
Works in conjunction with ____.
Ubiquitin-Protein Ligase (E3):
The most diverse group, with 500-1000 genes in humans. This step determines the ____.
Activation (E1), activates ubiquitin by loading it onto itself, requires ATP
Conjugation (E2)
substrate, E3 ligases
specificity of the ubiquitination process.
what is the most diverse ubiquitin enzyme group
ligase group (E3)
The ____ is a major type of E3 enzyme that regulates plant hormone signaling.
SCF complex
____ were first extracted from the pollens of Brassica napus (rapeseed or canola).
These hormones stimulate stem elongation and cell division but are present in ____ quantities
Brassinosteroids, extremely low
The ____ mutant was identified as part of studies on etiolation, a process in ____.
Normal Etiolation:
In the dark, plants ____ their stems (hypocotyl) to reach light, and cotyledons remain ____ and unexpanded.
DET2 Mutant Phenotype:
____ hypocotyl elongation.
Exhibited ____ cotyledons and even began synthesizing photosynthetic proteins in the dark, mimicking a ____ environment.
DET 2 mutant, plants grow in the absence of light
normal: elongate, folded
mutant: lacked hypocotyl elongation, expanded, light environment
____, the most active brassinosteroid, resembles human steroid hormones like ____, progesterone, and estrogen.
Like human steroids, brassinolide is an ____ molecule.
brassinolide, testosterone, isoprenoid
____: Regulates growth and development in darkness (etiolation).
skotomorphogenesis
Brassinosteroids, including brassinolide, are synthesized in the ____.
cytosol
The DET2 mutant lacks____, explaining its abnormal phenotype in the dark.
brassinolide
Scientists hypothesized the existence of a hormone that actively inhibits seed germination and bud sprouting during dormancy in plants.
Dormancy in seeds (annual plants) and buds (trees) was observed to be negatively regulated by such an inhibitory hormone: ____
Purification of Dormin:
The hypothetical hormone, initially called dormin, was isolated from ____ tissues entering dormancy in early autumn.
Dormin was found to be chemically identical to a compound that promotes abscission (shedding of leaves, fruits, or seeds), and was subsequently named ____ .
dormin, tree, ABA
Mutants like ____ in maize, which exhibit precocious germination, helped identify genes involved in ABA biosynthesis and signaling.
Vivipary in plants is analogous to animal viviparity, where embryos develop ____ instead of being laid as eggs (oviparity).
vivipary, inside the mother
High ABA leads to:
High GA leads to :
dormancy, germination
Under drought conditions, ABA levels ____ dramatically, triggering stomatal ____.
increase, closure to minimize water loss
how does ABA regulate stomatal closure:
ABA ____ cytosolic Ca²⁺ levels in ____ cells.
Elevated Ca²⁺ leads to ____, causing guard cells to shrink and close the stomatal pores.
increase, guard, ion loss
____ promotes abscission, the shedding of leaves, fruits, flowers, or seeds, allowing plants to conserve resources under stress.
ABA
ABA is synthesized in the ____
chloroplast
ABA is a breakdown product of a C40 ____ molecule, part of the terpenoid biosynthesis pathway.
isoprenoid
four major isoprenoid-based plant hormones:
cytokinin, brassinolide, ABA, gibberellin
