Plant Physiology Ch. 16 Signals from Light Exam 3 | Quizlet

The leaves of many species are able to bend toward the sun during its process across the sky, a phenomenon known as...

solar tracking

What is photoblasty?

seeds require light to germinate

Sunlight inhibits stem growth and stimulates leaf expansion in growing seedlings, two of several light-induced phenotypic changes collectively referred to as..

photomorphogenesis

What is phototropism?

A plant's response to light

ex: house plant will grow toward incoming light

In some species, leaves fold up at night called..

nyctinasty

In some species, leaves open at dawn..

photonasty

Many plants flower at specific times of the year in response to changing day length, a phenomenon called..

photoperiodism

The receptor molecules that plants use to detect sunlight are termed...

photoreceptors

___________ are photoreceptors that absorb red and far-red light most strongly, but they also absorb blue light and UV-A radiation

phytochromes

__________ detects red light

phytochrome

____________ detects blue light

cryptochrome and phototropin

Three main classes of photoreceptors mediate the effects of UV-A/blue light:

the cryptochromes, the phototropins, and the ZEITLUPE (ZTL) family

What do phototropins regulate?

phototropism, chloroplast movements, and stomatal opening

Cyrptochromes play a major role in..

plant photomorphogenesis

Phytochrome measures _________ and ________ of light

quantity; quality

What is photo-reversibility?

It is the process of when Pfr can revert back to inactive Pr in darkness, but this is a relatively slow process. However, Pfr can be rapidly converted to Pr by irradiation with far red light. Also referred to as photochromism

What is the role of the ZTL family?

they play roles in day length perception and circadian rhythms

What is the process of de-etiolation?

It is characterized by the produced of chlorophyll in dark-grown seedlings when exposed to light, results from the coaction of phytochrome absorbing red light and cryptochrome absorbing blue light from sunlight

An example: _________ light stimulates lettuce seed germination, and ________ light inhibits it

red light; far red light

What wavelength is determined high quality light and is good for photosynthesis?

< 700 nm

What wavelength is considered low quality light and is not good for photosynthesis?

> 710 nm (far red light)

How can the effects of red light be reversed?

By a subseqent irradiation with far-red light (710-850 nm)

In dark grown, or etiolated, seedlings, phytochrome is present in a red light-absorbing form, referred to as..

Pr

The cyan blue colored inactive form is converted by red light to a far-red light-absorbing form called..

Pfr

- active form of phytochrome

________ is partitioned between the cytosol and the nucleus

Pfr

At what wavelength will Pr convert to Pfr?

600 nm

At what wavelength will Pfr convert back to Pr?

730 nm

At night, what happens to Pfr sometimes?

It will spontaneously turn to Pr

What is escape from photoreversibility?

red light-induced events are reversible by far-red light for only a limited period of time, after which the response is said to have "escaped" from reversal control by light

- escape time is the time it takes for Pfr to complete its primary action

Phytochrome responses fall into three major categories based on the amount of light they require:

- very low fluence responses (VLFRs)

- low-fluence responses (LFRs)

- high-irradiance responses (HIRs)

Photomorphogenic responses to far red light are mediated predominantly by

phytochrome

Under which of the following conditions would the red:far-red ratio of ambient light be the lowest?

At night, when the only light available is from the moon and stars

Why do small seeds commonly need light exposure to germinate while larger seeds do not?

In the classical experiment of exposing lettuce seeds to short bursts of red and far red light in rapid succession, explain mechanistically why the germination response is photoreversible

This germination response is photoreversible because when Pr molecules are exposed to red light, which promotes germination, most of the photons are absorbed and converted to Pfr, which inhibits germination, is converted back to Pr with far red light

Red light promotes lettuce seed germination, but this effect is reversed by far-red light bc it inhibits germination

What is cryptochrome (1 pt) and describe at least two biological responses in plants mediated to cryptochrome

Cryptochromes are blue-light photoreceptors. Some biological responses include suppression of hypocotyl elongation, promotion of cotyledon expansion, membrane depolarization, inhibition of petiole elongation, anthocyanin production, and circadian clock entrainment

What was "the green revolution" and what hormone/hormone signal transduction pathway was principally affected

Why do small seeds frequently need exposure to light to germinate? What happens if a burst of red light is quickly followed by a burst of far red light?

Small seeds need light to activate the phytochrome system which helps the seed germinate. If there is a burst of red light, seed germination is initiated, but a burst of far-red light, seed germination is inhibited.

The shade avoidance response is controlled by phytochrome, and when a sun plant is shaded it will

Elongate its stems to grow as a spindly plant with few branches until it finds quality sunlight

Fill in the blank for the action or characteristic of phytochrome with either true or false (hint, three are true and three are false)

i. Phytochrome can shuttle between the cytoplasm and nucleus

ii. Phytochrome has kinase activity and can directly phosphorylate other proteins

iii. Phytochrome is needed for photosynthesis

iv. Phytochrome causes the response that Darwin observed in his experiments

v. Phytochrome helps plants detect the quality of light

vi. Phytochrome functions in the thylakoid membrane

1. false

2. true

3. false

4. true

5. true

6. false

Which of the following is true of the phytochrome system:

Pr (the inactive form) is converted to Pfr (the active form) by red light

Guard cells open stomata in response to light. The strongest stimulation to open is mediated by

cryptochrome

What are two ways that activated phytochrome can participate in signal transduction? (Hint: explain why some responses are fast and others are slow)

Phytochromes can sense red light and far-red light and there by signals the seeds to germinate, phototropism, stomal opening etc.

Phytochromes mediate signal transduction for the regulation of shade avoidance.

What is very low fluence response (VLFR)?

- Can be as low as 0.0001 umol/m2. Need about 1/10 of a firefly flash which can be enough to promote Arabidopsis germination and barley growth.

- These don't show reversibility because it needs 0.02% of phytochrome needs to be in the Pfr form

- Even with far-red exposure there if 3% of Phytochrome will be Pfr

What is low fluence response (LFR)?

They do show reversibility because they need more than 3% Pfr

Ex: Lettuce germination and stomata response

What is HIR?

high irradiance

- Need prolonged exposure and are not reversible

Responses to photoperiod - flowering

- If plants have too much light there will accumulate anthocyanin

What is skotomorphogenesis?

etiolated growth in darkness

What is true of blue light receptors (choose all that are true)

Plants growing toward directional light is primarily a response to blue light

Blue light can trigger stomata to open faster and larger than red light alone

Blue light is involved in the photo-reversibility of germination in lettuce seeds

Blue light triggers chloroplast movements when light intensity becomes strong

They are activated by blue Dwavelengths and inactivated by UV wavelengths

- Plants growing toward directional light is primarily a response to blue light

- Blue light can trigger stomata to open faster and larger than red light alone

- Blue light is involved in the photo-reversibility of germination in lettuce seeds

- Blue light triggers chloroplast movements when light intensity becomes strong

Stomatal opening is regulated by..

blue light

Both ________ and __________ inhibit stem elongation

phytochrome; cryptochrome

____________ interacts with ____________ to regulate late flowering, and both types of photoreceptors are necessary to maintain circadian cycles

phytochrome; cryptochrome

_____________ mediate photoresponses to blue light

phototropins

When phototropins are activated by blue light, their kinase is "uncaged" causing...

autophosphorylation

What are good bio-assays for blue light response?

guard cells and stomata opening

Explain shade avoidance

Shade from other plants inactivates Pfr to Pr and gibberellins then promote internode elongation. When the branch finds high quality light again, Pr converts to Pfr and gibberellin mediated elongation stops.

ex: Wild corn will grow tall and spindly if overcrowded; modern corn does not have this shade response and will grown normally at high density