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28 Cards in this Set

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How do plants respond to environmental cues:
1) through evolution (very long term)

2) growth differences (trees vs. wind; yrs)

3) change developmental processes (make roots or leaves, wks)

4) change physiological processes (CAM responds to day vs. night)
What controls responses over the course of a plants life?
hormones
what are hormones?
chemical produced in one part of body and affects another part of the body.

- actions are specific and they affect specific tissues

- active in minute concentrations.
Who discovered the first hormone?
Darwin and Darwin
What was the first hormone discovered?
the hormone responsible for phototropism
coleoptile:
grows straight up in normal overhead light and in the dark

- grows toward light when the light comes form one side.
define tropisms:
growth responses towards or away from a stimulus
what are 3 examples of tropisms?
1) gravitropism

2) phototropism

3) thigmotropism
define thigmotropism:
directional growth in response to touch.

- touching a plant at a site, has been demonstrated to slow growth at that site.

----- if one side of a vine or tendril is touching something.... that side will grow slowly and the other side will grow more quickly
What is thought to be the cause of thigmotropism?
an increased ethylene in response to mechanical stimulation ---> decreased cell elongation at site of stimulation
define circadian rhythm:
responses that are based on a 24 hr. time period.
define biological clock:
the internal clock that allows circadian rhythms to occur.

- are usually set by the light/dark cycle of the sun.
what do biological clocks modulate (control)?
- metabolism/ metabolic rate

- cell division rate

- blood cell deposition into blood stream

- alertness

etc....
In plants what do biological clocks modulate (control)?
- metabolism/ metabolic rate

- opening and closing of stomata

- legume sleep movement

- long term growth responses to day length

etc....
define photoperiodism:
responses dependent on day vs. night length.
Plants need to be able to tell when the change of seasons occur for.... in other words photoperiodism controls?
- seed germination

- flowering

- entering or breaking winter or summer dormancy
what is photoperiod?
the determination of relative length of day vs. night.
Describe the best studied example of photoperidism
study used a variety of mutant tobacco (Maryland mammoth)
- it grew tall in summer, but would not flower during the summer, finally flowered in dec. in a greenhouse.

- found that it was short winter days that induced plant to flower.
---- by manipulating the daylight period so that the day was 14hrs. or shorter, they were able to induce flowering.
What is the mutant tobacco called a short day plant?
because it was a shortened day that induced flowering.

ex: soy and poinsettias.
what are some plants called long day plants?
because they flower when days are longer than a certain period of time.

ex: plants that flower in the summer, spinach flowers...
What are day neutral plants?
plants that flower at a certain maturity stage and are not photoperiodic

ex: tomato
it was discovered that it was not day length but actually _______ length that was the controlling factor in photoperiodism plants.
night length
flowering and night length:
Phytochrome:
- a light absorbing protein pigment

- exist in leaves

- the protein is a dimer and an enzyme and it exists in 2 states.

- can be turned on and off by red light.
what occurs when phytochrome is flashed with red light at night?
the night is interrupted and flowering is inhibited.
What occurs if the phytochrome is shined with red light twice?
what does photoreversible mean?
Describing any compound or system that can exist in two forms, and can be changed from one to the other by the appropriate influence of light.
Phytochromes allow plants to adapt to certain conditons such as and fine tuning of?
- day/night length
- light intensity
- light quality (wavelength)

fine tuning of:
- flowering time
- growth spurts
- breaking dormancy
- seed germination