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what is Signal Transduction?
a process in which a cell converts and amplifies an extracellular signal into an intracellular signal that affects some function in the cell
what are the responses of signal transduction?
transcriptional or post-translational modification
what is transcriptional modification?
when DNA is transcribed into RNA
what is post-translational modification?
RNA into proteins
what is Etiolation?
when a plant tries to grow without light, it is pale, the stem elongates, leaf expansion is reduced
what is De-etiolation?
when the plant grows with access to light, and the plant becomes more green
what is a phytochrome?
a protein and light sensing molecule
what happens during reception
the phytochrome that has a protein senses light and is activated
what happens during transduction
the phytochrome activates the cGMP or the Ca2+ channel opening
what is the definition of a Hormone
a chemical produced by one part of the body and then is transported to another where it binds to a specific receptor on or in a target cell which then triggers a response
what is the conclusion of the Darwin and Darwin bending vs opaque and clear tip cap?
that the coleoptile is a sheath that on a young plant. At the tip of the plant is the sheath that causes the plant ot bend toward the light
what is the conclusion of the Boyson Jensen experiment with the permeable gelitin and the impermeable?
that its the chemicals at the tip of the plant that causes the bending throughout
what is the conclusion of the Went experiment
that the chemical Auxin which loosens cellulose and causes elongation on that side of the plant
what does Auxin do?
stimulates stem elongation at low concentrations
promotes growth of lateral and adventitious roots
regulates fruit development
enhances apical dominance
functions in phototropism and gravitropism
promotes vascular differentiation
retards leaf abscission
what does Cytokinins do
regulates cell division in roots and shoots
modify apical dominance
promotes lateral bud growth
promotes movement of nutrients
stimulates seed germination
delays leaf senescence
what do Gibberellins do?
stimulate stem elongation, pollen development, pollen tube growth, fruit growth, seed development/ germination
regulates sex determination and transition from juvenile to adult phases
What does Abscisic Acid do?
inhibits growth
promotes stomatal closure during drought
promotes seed dormancy
inhibits early germination
promotes leaf senescence
promotes desiccation tolerance
What does Ethylene do?
promotes ripening, leaf abscission, triple response in seedlings
enhances rate of senescence
promotes root and hair formation
promotes flowering in pineapples
What is the triple response in seedlings
stem thickens, stops growing upward, bends to the light, forms a curve
What do Brassinosteroids do?
promotes cell expansion and division in shoots
promotes root growth at low concentrations
inhibits root growth at high concentrations
promotes xylem differentiation
inhibits phloem differentiation
promotes seed germination and pollen tube elongation
What does Strigolactones do?
promotes seed germination, the control of apical dominance, and the attraction of mycorrhizal fungi to the root
what does signal transduction allow for?
the chemicals to work inside the cell
what is Photomorphogenesis? What is it regulated by?
the effect of light on plant growth and development
this is regulated chiefly by blue and red light
What what is phototropism? What is it affected by?
bending towards or away from light, light induced opening of the stomata, light induced slowing of hypocotyl elongation when seedling beaks ground
affected by blue light
what are red light photoreceptors called?
phytochromes
Phytochromes exist in what two interconvertable forms?
Pr and Pfr
these depend on the type of light
What does the Pr phytochromes do?
absorb red light and is converted to Pfr
What does the Pfr phytochromes do?
absorbs far red light and is converted to Pr
Which form (Pr or Pfr) triggers the developmental responses of plants to light?
Pfr
The biological clock controls what in plants?
circadian rhythmns
Definition of biological clock
the internal timer that approximates a 24 hr cycle
Definition of circadian rhythm
the internal physiological cycle of about 24 hrs that persists even in the absence of external cues
What are two examples of circadian rhythms in plants?
the opening and closing of stomata independent of light and darkness
sleep movement in shamrocks and beans
What entrains the biological clock to exactly 24 hrs?
light
How does light entrain the biological clock to exactly 24 hrs?
through photoreceptors (blue-light and red-light)
In red-light photoreceptors, the phytochrome conversion marks what?
sunrise and sunset, providing the biological clock with environmental cues
Definition of photoperioism?
physiological response to relative lengths of night and day
What does photoperiodism determine?
time of seed germination, onset and breaking down of bud dormancy, and time of flowering
a short day plant requires what to blossom?
a short day and a long night with no interruptions to blossom
which is more important for blossoming: short day or long night?
long night
For a long day plant, which is more important: a short night or long day?
a short night
In short day plants, the light period is… and when do they flower?
shorter than a critical length
flower in late summer/fall
In long-day plants the light period is… and when does it usually flower?
longer than a critical length
flowers in spring/ early summer
day-neutral plants are…
unaffected by the photoperiod
short day plant =
long day plant =
short day plant = long night plant
long day plant = short night plant
what is the effect of a brief dark period during the day?
nothing
what is the effect of a brief light period during the dark?
no blossoming, depending on the type of light (Pr or Pfr)
what does the P represent?
the phytochrome molecule
Pfr is ___ blooming
active
Pr is ___ blooming
inactive
With a single burst of Pr light during the night, what happens to the blooming?
the Pr is converted to Pfr and the plant recognizes it as a short night
With a burst of Pr then Pfr red light during the night, what happens to the blooming?
the Pfr is converted back to Pr, and the plant recognizes it as a long night
During a short day, will a long day plant grafted to a short day plant blossom? What flowering hormone is present?
yes, florigen
What is gravitropism? What are the types?
the response of a plant to gravity (positive and negative)
positive gravitropism
negative gravitropism
positive is roots down
negative is shoot up
What is thigmotropism?
mechanical stimuli, the response of a small plant to contact witht he touch of an object, animal, plant, or wind
ex. tendrils
What are environmental stresses on plants?
Drought → plants increase demand for water, release hormone, close stomata, grow deeper roots
Flooding → produce ethylene to create air tubes
Salt → lowers water potential and causes inability to absorb water
Heat → kills plant enzymes, heat proteins are produced to help protect the pant
Cold → alters the lipid concentration and produces unsaturated fatty acids to keep the plant from freezing
