Plant Physiology Ch. 15: Signal Transduction | Quizlet

What does the signal transduction in plants usually involve?

"repressing a repressor"

- ON to begin with and a negative regulator is removed

What is the first plant hormone to be discovered?

auxin

An environmental input that initiates one or more plant responses is referred to as a..

signal

The physical component that biochemically responds to that signal is designated a..

receptor

Once receptors sense their specific signal, they must __________ the signal in order to amplify the signal and trigger the cellular response

transduce

Receptors trigger the cellular response by employing intracellular signaling molecules called..

second messengers

All signal transduction pathways typically involve the following chain of events:

Signal --> receptor --> signal transduction --> response

In a ______________ to an environmental signal, both signal reception and response occur in the same cell

cell autonomous response

A _____________ is one in which signal reception occurs in one and the response occurs in distal cells, tissues, or organs.

non-cell autonomous response

What is the general scheme for signal transduction?

- environmental or developmental signals are perceived by specialized receptors.

- a signaling cascade is then activated that involves second messengers and leads to a response by the plant cell.

- when an optimal response has been achieved, feedback mechanisms attenuate the signal

Where are receptors located?

• plasma membrane

• cytosol

• endomembrane system

• nucleus

__________ is the most ubiquitous second messenger in plants and other eukaryotes

Ca^2+

What is the difference between animal cascades and plant cascades?

- animal signal transduction cascades are a series of positive steps

- plant signal transduction cascade usually involves "repressing a repressor" or inactivate a repressor

What do secondary messengers do?

amplify the signal

What can secondary messengers include?

• Ca^2+

• pH changes

• modified lipids

• reactive oxygen species

What are secondary messengers?

small molecules and ions produced or mobilized in relatively high levels after signal perception, and act in the signal cascade between the receptor and response

What are the four ways that plants can increase the pool of active hormones?

1. biosynthesis

2. activation

3. release from internal stores

4. uptake

What are four ways that plants can decrease the pool of active hormones?

1. degradation

2. inactivation or conjugation

3. sequestration

4. efflux

What does the chemical structure of auxin look like?

What does the chemical structure of a gibberellin look like?

What does the chemical structure of cytokinin look like?

What does the chemical structure of ethylene look like?

What does the chemical structure of abscisic acid (ABA) look like?

What does the chemical structure of brassinosteroids look like?

Which statement is the most FALSE regarding signal transduction cascades in plants?

Plant cascades are usually a positive activation step

A secondary messenger in a signal transduction cascade..

transmits the signal from the receptor to the site of the response

What are the 5 "classic hormones"

- auxin

- gibberellin

- cytokinin

- abscisic acid

- ethylene

What was the first growth hormone to be studied?

auxin

Who discovered the existence of auxin?

Charles and Francis Darwin

How did the Darwins discover auxin?

They studied the bending of seedling sheath leaves (coleoptiles) of canary grass and seedling hypocotyls of other species in response to undirectional light, and concluded that a signal produced at the apex travels downward and causes lower cells on the shaded side to grow faster than on the illuminated side. The signal was a chemical that could diffuse through gelatin blocks and was subsequently named auxin.

Where is auxin produced?

in the apical meristem and young organs

Auxin promotes...

cell elongation and tissue expansion

______________ are used widely in agriculture and horticulture to promote flowering and fruiting and control weeds (2,4-D)

synthetic auxins

__________ work together with auxin to control cell division and differentiation

cytokinin

What hormone are regulators of cell division in plants?

cytokinin

__________ slow aging of some organs by inhibiting protein breakdown, stimulating RNA and protein synthesis, and mobilizing nutrients from surrounding tissues

cytokinin

ex: lettuce is genetically engineered to make more cytokinin so it stays fresher longer

What is the function of gibberellins?

regulators of plant height, seed germination, and flowering

ex: think of grapes

What are some effects of gibberellin?

stem elongation, fruit growth, and seed germination

- commercially used to promote growth in grapes, and grain germination for malting to stimulate breakdown of starch in endosperm

What hormones slows growth?

abscisic acid (ABA)

What are the effects of abscisic acid?

- promotes seed dormancy and prevents premature germination

- promotes drought tolerance

In drought, ___________ causes rapid efflux of K+ and H2O from guard cells causing stomata to close and prevent water loss

abscisic acid (ABA)

An example of hormones having antagonistic functions would be __________________ promoting seed maturation and dormancy and _______________, which promotes seed germination

abscisic acid; gibberellin

When Agrobacterium tumefaciens infects a plant to form a crown gall, it transfers to the plant genes that promote the synthesis of the hormones ______________ and ______________.

auxin; cytokinin

When auxin promotes cell wall expansion, it does so by:

Enhancing activity ATPase to pump protons into the extracellular space

Which of the following statements is true of receptors in a signal transduction cascade

The receptor can be anywhere in the cell that the signal can reach

The fundamental chain of events in a signal transduction cascade is

Signal → Receptor → Signal Transduction → Response

__________ promotes seed maturation and dormancy, and antagonizes GA, which promotes germination

ABA

In response to drought, _________ promotes stomatal closure and favors root growth

ABA

What is the gaseous hormone involved in ripening?

ethylene

A burst of __________ in a fruit triggers the ripening process

ethylene

Plants produce ethylene in response to what kind of stresses?

drought, flooding, mechanical pressure, injury, and infection

What is senescence?

the programmed aging and death of plant cells, organs, or whole plants and is associated with a burst of ethylene

A change in the balance of ________________ controls leaf abscission (the process that occurs in autumn when a leaf falls)

auxin and ethylene

In a plant phosphor-relay system, which are thought to be derived from bacterial two-component signaling cascades,

A phosphate is passed from a sensor histidine kinase to a histdine phosphotransfer protein (Hpt) and then to a response regulator (ARR)

Ethylene response includes...

senescence, leaf abscission, and fruit ripening

What do brassinosteroids regulate?

photomorphogenesis, germination, and other developmental processes

- cell devision, cell elongation, germination, etc

What do strigolaactones do?

they suppress branching and promote rhizosphere interactions

- suppress shoot branching and stimulate cambial activity and secondary growth

What is IAA biosynthesis associated with?

rapidly dividing and growing tissues, especially in shoots

What are the primary sites for auxin synthesis?

shoot apical meristems, young leaves, and young fruits

Why are synthetic auxins more effective than natural auxins?

the synthetic auxins are much less subject to homeostatic control -- degradation, conjugation, transport, and sequestration -- than natural auxins are

Gibberellins are synthesized by oxidation of the ..

diterpene ent-kaurene

Ethylene is synthesized from..

methionine via the intermediate ACC

Abscisic acid is synthesized from..

a carotenoid intermediate

An example of hormones having antagonistic functions would be __________ promoting seed maturation and dormancy and _________ which promotes seed germination

ABA; gibberellin

An example of hormones having cooperative functions would be ___________ promoting differentiation into roots, and ____________ promoting differentiation into shoots

cytokinin; auxin

What are phosphorelay systems?

a series of phosphate regulated intermediates

- ancient and found in bacteria

- two-component relay system

- signal activates Histidine kinase

- Kinase causes phosphorylation of the response regulator

- histidine phosphotransfer protein (HPT) is going to shuttle between the cytoplasm and the nucleus

- it is going to take that phosphate and transfer it

- ARR --> Arabidopsis response regulator

- Type B --> transcription factors

- Type A --> phosphorylate some other protein/enzyme to activate or repress a response

True or False: Hormones can signal cells within, nearby, or far way from their site of synthesis

true

Cytokinin and ethylene pathways use derived ______________, which involve membrane bound sensor proteins and soluble response regulator proteins

two component regulatory systems

Brassinosteroids and certain auxin pathways use _______________ to phosphorylate serine or threonine regions of target proteins

transmembrane receptor-like kinases (RLKs)

Abscisic acid pathways use ______________ as well as kinases

phosphatases