Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

PLBI 403 > Final > Flashcards

Final Flashcards

1
Q

When does signal transduction occur

A

When an extracellular signalling molecule activates a specific receptor on the cell surface or inside of the cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does activation of a receptor in signal transduction cause?

A

A biochemical chain of events inside the cell, creating a response alters the cell’s metabolism, shape, gene expression, or ability to divide

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

The signal from signal molecules can be —— at any step

A

Amplified

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Can one signal cause many reponses

A

Yes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the two types of signal transduction mutation

A

Signal hyposensitive mutations
Signal hypersensitive mutations

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Signal hyposensitive (or insensitive) mutations

A

Signal but no response

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Signal hypersensitive (or constitutive) mutations

A

No signal but response

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How are forms and functions of multi-cellular organisms achieved?

A

By sophisticated communications among cells, tissues, and organs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Chemical signals from one part of the body to another coordinate

A

Morphogenesis and physiology (interactions with environments) of plants.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Chemical messangers are _____

A

Hormones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Example of enviornmental or develepmental signal

A

Light, temperature, touch, hormone, nutrient

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Example of receptor

A

Receptor kinase, G-protein-coupled receptor, F-box protein, ion channel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Example of signal transduction pathway

A

Repressor protein degration, protein phosphorylation, second messengers, (action potential/membrane voltage)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Example of signal transmission

A

Hormone transport, electrical signaling

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Example of response

A

Transcriptional (gene expression), posttranslational (cytoskeletal, reorganization, enzyme de/activation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the six major plant hormones?

A

Auxin
Cytokinin
Gibberellin
Ethylene
Abscisic acid
Brassinosteroid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is Auxin (IAA) signal transduction

A

de-repression by protein degradation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is cytokinin signal transduction

A

Prokaryote two-component system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is gibberellin (GA) signal transduction

A

de-repression by protein degradation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is ethylene signal transduction?

A

Prokaryote two-component system

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is abscisic acid (ABA) signal transduction

A

de-repression involving kinase and phosphotase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is brassinosteroid signal transduction

A

de-repression involving kinase and phosphotase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What are the minor plant hormones

A

Strigolactone
Jasmonic acid
Salicylic acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Plant hormone structures

A

Other than ethylene every hormone has at least one ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is a cotyledon?

A

An embryonic leaf of seed bearing plants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is a hypocotyl?

A

The part of the stem of an embro plant beneath the cotyledon

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What does the de-etiolation2 (DET2) mutation show?

A

A shortened hypocotyl and expanded cotyledons in dark.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the function of brassinosteroids?

A

Can stimulate stem elongation and cell division, was first isolated from the pollens of Brassica napus (rapeseed or CANOLA) in 1979 and thus named as brassinosteroid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is etiolation?

A

A process in flowering plants grown in partial or complete absence of light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What does DET2 encode?

A

A reductase enzyme involved in the synthesis of brassinolide [human steroid (or isoprenoid) sex hormone-like molecule].

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What do brassinolides play a pivotal role in?

A

Plant development, including cell elongation, skotomorphogenesis, germination, leaf senescence.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Where are brassinolides synthesized?

A

In the cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

The molecular cloning suggests that brassinolide is a ________

A

Necessary hormone for Etiolation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What is abscission?

A

The shedding of various parts of an organism, such as a plant dropping a leaf, fruit, flower, or seed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What does ABA negatively regulate

A

Seed germination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What hormone balance determines dormancy?

A

ABA:GA

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

What happens to ABA levels in drought conditions

A

Increase dramnatically to trigger signaling for stomata closure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

What causes the stomata to close when ABA levels are increased?

A

Ca2+ which is used as a messenger to causes the physiological changes in stomata

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Where is ABA synthesized?

A

Chloroplast

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What molecule is ABA a breakdown product from?

A

C40 isoprenoid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

How many of the 6 major hormones are isoprenoid?

A

Four

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Where are C15, C30 synthesized?

A

Cytosol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

Where are C10, C20, and C40 synthesized

A

Chloroplast

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What did the first notion of auxin come from?

A

Darwin’s phototropism experiments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

What does auxin mean?

A

To grow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

What type of experiments proved the prensce of a chemical substance regulating cell growth

A

blue-light phototropism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

What is the optimal concentrayion of auxin for cell elongation?

A

10^-6 to 10^-5

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

What is auxin consdiered in plants?

A

Morphogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What is auxin?

A

Indole-3-acetic acid (IAA)
Several different bioactive auxins have been identified, but IAA is the most abundant and active auxin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

Where is auxin from?

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Cytokinin

A

Cell division

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

Where are new cells supplied from?

A

Meristem cells (shoot and root)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

What is plant tissue culture

A

Indefinite cultivation of plant cells in the medium containing sucrose, mineral salts, and vitamins, like we culture bacteria in the medium.
Plant tissue culture cannot be achieved by auxin alone because cells cannot divide, suggesting that cell-division promoting factor is required.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

Two streams of research resulted in the identification of a chemical substance for cell division.

A

a) Screening various naturally occurring or synthetic compounds for cell-division activity.
- Bioassay-based screening, purification, structural elucidation, and chemical synthesis.

b) Studies of the crown gall forming bacteria - Agrobacterium tumefaciens.
- Molecular genetics and biochemistry

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

Chemical purification

A

Philip White discovered that coconut milk has a substance which supports the continued cell division of mature, differentiated cells. But the substance could not be purified.

In 1950s, Skoog identified that aged or autoclaved herring sperm DNA has a potent cell-division promoting activity. This substance was purified, and its structure was determined.

Adenine derivative. MS medium was named after his name (MS = Murashige and Skoog medium).

In 1973, Letham isolated a new cell-division promoting substance from the immature maize endosperm.

This is named Zeatin. Although several other zeatin derivatives were also found to be active in cell-division, zeatin is widely accepted as a dominant cytokinin in plant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

What is the dominant cytokinin in plants

A

Zeatin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Where is zeatin synthesized?

A

In chloroplast from ATP and DMAPP (dimethyl allyl diphosphate).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

What is a key enzyme in zeatin biosynthesis?

A

IPT (Isopentenyl transferase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

What is fasciation?

A

An abnormal growth of plant tissues

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

What can an abnormal occurrence of apical meristems facilitate

A

The cell growth perpendicularly to the direction of main stem (or root) growth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

Studies of Agrobacterium tumefaciens

A

A. tumefaciens can infect wounded tissues and alters plant cells to form tumor-like tissue (called a gall).

Infected plant cells continue to divide throughout the life-cycle of the plants, and form an entirely unorganized mass of tumor cells.

The gall was isolated and treated with 42 degree heat, which can kill A. tumefaciens but plant cells can survive this heat treatment. Then this bacteria-free gall could be cultured in hormone-free medium. -> undifferentiated callus tissue are growing forever, can it give a hint on cancer?

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

What does T-DNA encode genes for?

A

auxin, cytokinin, and octopine biosynthesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

Wht is suxin synthesized from?

A

tryptophan, and the modified cytokinin by bacterial enzyme.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

What is octopine derrived from?

A

arginine and alanine, and no organism can utilize the octopine as a carbon source except A. tumefaciens.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

What determines morphogenesis in cultured tissues?

A

Auxin:cytokinin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

When auxin is high and cytokinin is low we see

A

only root growth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

When auxin is low and cytokinin is high we see

A

Only stem/leaf growth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

When auxin is intermediate and cytokinin is intermediate we see

A

no growth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

_____, ______ and _______ play essential roles in plant genetic enegineering

A

Auxin, cytokinin and agrobacteria

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

Gibberellins (GA)

A

When purified GAs were applied to plants, a spectacular response in stem elongation was observed in dwarf and rosette plants.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

Where is gibberellin synthesized?

A

In chloroplast, endoplasmic reticulum (ER) and cytosol.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
72
Q

At least ___ different GAs have been identified from different species

A

136

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
73
Q

Seedless fruits can be made by either:

A

the fruit develops without fertilization (parthenocarpy), or pollination triggers fruit development, but the ovules or embryos abort without producing mature seeds (stenospermocarpy)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
74
Q

GA treatment can _______ the berry size and fruit stalk (pedicel) length,

A

increase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
75
Q

Synthetic ethylene and its analogs cause

A

Dramatic physiological changes in plants

Used to control the post-harvest ripening process of fruits.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
76
Q

coal gas resulted in _______ in trees around the street lamps.

A

defoliation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
77
Q

ripened fruit emits ________ to facilitate the ripening of the immature (unripen) fruit.

A

gaseous chemical

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
78
Q

we can alleviate the post-harvesting problem if we ______

A

Can control either the endogenous ethylene biosynthesis or the ripening progress by an external ethylene treatment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
79
Q

What AA is precursor in ethylene formation

A

MET

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
80
Q

Climacteric fruits

A

Show a steady respiration rise before the ripening, and then shows a spike of ethylene production immediately before the respiratory rise.

Sensitively responds to the externally applied ethylene. This is due to autocatalytic effect (or positive regulatory loop).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
81
Q

Non-climacteric fruits

A

Do not show the same pattern of respiration and ethylene production

Difficult to control

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
82
Q

What is veraison

A

The onset of ripening in grapevine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
83
Q

Similarity between animal and
plant signal transduction

A

“Kinase” and “phosphatase” are important signal delivering components in both plant and animal.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
84
Q

What is the function of kinase

A

adds phosphates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
85
Q

What is the function of phosphotase

A

Removes phosphates

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
86
Q

What does a kinase cascade do?

A

Amplifies signals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
87
Q

Difference 1 between plant and animal signal transduction

A

GPCRs are NOT playing any important role in plant signaling transduction.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
88
Q

What are G protein-coupled receptors (GPCRs) involved in?

A

Hormones, odors, flavors and light in animals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
89
Q

Difference 2 between plant and animal signal transduction

A

Plant signal transductions have evolved from both eukaryotic and prokaryotic ancestors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
90
Q

What is one example of a prokaryotic signal transduction has been identified in plants

A

Crytochrome and two-component systems in plants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
91
Q

Difference 3 between plant and animal signal transduction

A

Signals can be sensed at many different subcellular sites in plants.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
92
Q

Where can signals be sensed in plants?

A

Brassinosteroid: Plasma-membrane.
Cytokinin: Plasma-membrane.
Red-light: cytosol.
Blue-light: Plasma-membrane (Phototropin).
Ethylene: Endoplasmic reticulum
Blue-light: Nucleus (Cryptochrome)
Blue-light: Chloroplast Thylakoid (Zeaxanthin)
Auxin: nucleus (SCFTIR1).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
93
Q

Difference 4 between plant and animal signal transduction

A

Inactivation of repressor protein (de-repression) is common in plant signal transductions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
94
Q

What is ubiquitin

A

small regulatory protein (8.5 kDa), 4 genes in human

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
95
Q

Role of Ubiquitin-activation enzyme (E1 enzyme):

A

Load (activate) an ubiquitin to E1 protein, 9 genes in human

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
96
Q

Role of Ubiquitin-conjugation enzyme (E2 enzyme)

A

obtain an ubiquitin from E1, and transfer the ubiquitin to the substrate proteins specified by E3. 20-30 genes in human

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
97
Q

Role of ubiquitin protein ligase (E3 enzyme):

A

Adapter proteins specifying substrate proteins. 500-1000 genes in human

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
98
Q

What is the most common type of E3 enzyme?

A

SCF protein

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
99
Q

What does SCF protein consist of?

A

SKP + Cullin + F-box subdomains.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
100
Q

What do these names mean? SCFTIR1 or SCFCOI1 or SCFSLY1

A

Transporter inhibitor response 1, coronation insensitive 1, sleep 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
101
Q

What is Molecular Glue theory

A

A term coined to describe the mechanism of action of the plant hormone auxin and subsequently used to characterize synthetic small molecule protein degraders exemplified by immune-modulatory imide drugs (IMiDs)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
102
Q

What did chemical genetic screening identified Pyrabactin (PYR) as

A

An agonist

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
103
Q

What does ABA signaling involve?

A

An interaction between phosphatase and kinase activity.
(This is also a de-repression-type regulation, involving kinase and phosphatase)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
104
Q

What does phosphorylation of the key regulator (SnRK2) lead to

A

Activation of ABA actions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
105
Q

Brassinolide signaling

A

Also a de-repression –type regulation, involving kinase and phosphatase.
1. BSU1 = phosphatase
2. Bin2 = kinase
3. BZR1, BES1 = transcription factor
4. Phosphorylated BZR1/BSE1 will be removed from the nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
106
Q

The signaling unit is repressed in brassinolide signaling when

A

There is no brassinolide but when brassinolide activates BUS1 (phosphatase), BUS1 in turn activates BIN2 by dephosphorylation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
107
Q

What has been the major cause of crop loss in agriculture

A

Lodging

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
108
Q

What is lodging

A

a bending of stems to the ground due to the weight of water collecting on the ripened heads. > harvesting becomes difficult.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
109
Q

What does a shorter inter-node do?

A

Reduces lodging

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
110
Q

What has been done to combat lodging?

A

A number of chemical inhibitors that block the biosynthesis of GA have been developed and used for greenhouse (e.g., lilies, chrysanthemum) and for wheat.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
111
Q

The “Green Revolution” in 1960s are due to

A

the introduction of high yielding dwarf varieties of wheat and rice into Latin America and Southeast Asia, such as wheat GA-insensitive dwarf mutant, called Reduced height (Rht).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
112
Q

What is believed to allow human population growth?

A

the breeding research for dwarf mutants

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
113
Q

Describe the mutation in wheat GA-insensitive dwarf mutant, called Reduced height (Rht).

A

This is a mutation in DELLA domain in DELLA protein.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
114
Q

Why does a mutation in DELLA domain cause dwarf phenotype?

A

Similar to auxin signal perception, but it has GA receptor and negative regulator.
GID1 (GA insensitive dwarf 1) is GA receptor.
FORMATION OF THE GA-GID1-DELLA COMPLEX
PROTEASOME-DEPENDENT DEGRADATION OF DELLAS
PROTEIN DEGRADATION

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
115
Q

A mutation in DELLA domain (of DELLA) will make DELLA

A

resistant to degradation.
unable to block downstream transcription factors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
116
Q

What is the action domain?

A

GRAS domain
Functional domain

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
117
Q

DELLA (Asp-Glu-Leu-Leu-Ala) protein has

A

DELLA domain and GRAS domain.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
118
Q

The DELLA domain is the _____ domain

A

regulatory

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
119
Q

The GRAS domain is the _____ domain

A

functional

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
120
Q

When were distinct developmental variations observed

A

When plants were grown in dark and light.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
121
Q

Plant developmental process in dark is called

A

Skotomorphogenesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
122
Q

Plant developmental process in light is called

A

photomorphogenesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
123
Q

Development under like is characterized by:

A

Decrease in the rate of stem elongation.
Apical-hook straightening
Initiation of the synthesis of pigments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
124
Q

Blue light wavelengths

A

400-500

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
125
Q

Red light wavelengths

A

650-680

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
126
Q

Far red light wavelengths

A

710-740

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
127
Q

Lettuce seed germination is a _______ response

A

photo-reversible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
128
Q

Two hypothetical models for light sensors and responses in plants

A
  1. Two light sensors are present in plants – one for red-light and the other for far-red light. They work antagonistically.
  2. One light sensor plays two distinct roles in two interconvertible forms – photoreversible molecule.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
129
Q

Which of the hypothetical models is correct?

A

The second
Two light sensors are present in plants – one for red-light and the other for far-red light. They work antagonistically.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
130
Q

What is a phytochrome

A

A superfamily of photosensory receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
131
Q

In dark seedling, phytochrome is present as

A

a red-light absorbing form (Pr), and it is converted to a far-red light absorbing form (Pfr) by red-light

132
Q

What can far-red light do to Pfr

A

Convert it to Pr

133
Q

What can red light do to Pfr

A

Convert it to Pr

134
Q

IS Pfr or Pr the physiologically active form

A

Pfr

135
Q

Is phytochrome pool ever fully converted to the Pfr or Pr form, following red or far-red irradiation

A

NO

136
Q

How does phytochrome sense light and deliver signals?

A

Using Holoproteins =
Chromophore + Apoprotein

137
Q

Chromophore is ______

A

phytochromobilin

138
Q

What is phytochromobilin covalently bonded to?

A

A cysteine residue

139
Q

Where is phytochromobilin synthesized

A

Chloroplast

140
Q

Attachment of phytochromobilin to apoprotein is ________

A

autocatalytic

141
Q

Molecular structure and proposed mechanism of phytochrome

A

Two domains : N-terminal sensing and C-terminal action domains.

142
Q

WHat is PRD involved in

A

Dimerization

143
Q

What does Red-light convert cis form to

A

Trans form which causes a conformational change of phytochrome.

144
Q

Pfr protein relocates to ____ to induce gene expression resulting in photomorphogenesis

A

nucleaus

145
Q

Phytochromes can phosphorylate other proteins, can be phosphorylated by other proteins, can degrade other proteins what are some examples of this?

A

Phytochrome Interacting Factors (PIF);
Phytochrome kinase substrate (PKS)

146
Q

What does early signalling involve?

A

The rapid degradation of PIFs

147
Q

What does lag time?

A

The time-gap between red-light reception and physiological response

148
Q

What is escape from photoreversibility

A

After a certain time, red light-induced response cannot be reversed by far-red light

149
Q

What is fluence

A

The amount of light measured in (µmol quanta m^-2)

150
Q

What is irradiance or fluenece rate?

A

The amount of light in a given time measured in (µmol quanta m^-2 s^-1)

151
Q

What are the three classes of responses that were found?

A

VLFR (Very low Fluence Response)
LFR (Low Fluence Response)
HIR (High irradiance response)

152
Q

VLFR

A

Reciprocity applies, not FR-reversible

After treating seeds with some chemicals or stresses (e.g., ethanol and chilling), the sensitivity of seeds of some species to Pfr can be increased several orders of magnitude.

A flash of light for a second (0.001 – 0.1 µmol quanta m-2 ) is sufficient to induce Arabidopsis germination.

Germination of sensitized seeds can be triggered by light treatments that establish < 0.02 % Pfr.

Agricultural observation – Tillage in dark can markedly reduce the occurrence of weeds. It is likely that seeds of some plant species becomes sensitized when they are buried under deep soil for a long time.

153
Q

LFR

A

Reciprocity applies, FR-reversible

LFR occurs between 1 and 1000 umol quanta m-2

Most of the red- and far-red light reversible responses

Total fluence [ = fluence rate (or irradiance) x time] determines whether LFR occurs or not.

Reciprocal relationship between irradiance and time -> Law of reciprocity

Both VLFR and LFR follow the law of reciprocity.

154
Q

HIR

A

Fluenece rate dependent, long irradation required and not photo-reversible, reciprocity does not apply

HIR requires continuous exposure to light of relatively high irradiance.

Irradiance (fluence rate) determines whether HIR occurs or not (not fluence amount!).

HIR saturates at much higher level of fluence (>100 times).

HIR does not obey the law of reciprocity.

Not photo-reversible

155
Q

Discovery of blue-light response

A

Some physiological events (e.g., phototropism) could not be perfectly explained by two major light-responses (photosynthesis and phytochrome).

These physiological actions appear to be responsive to blue-light (400- 500 nm) – action spectrum.

Therefore, it appears that some cryptic signaling mechanisms (distinguishable from the photosynthesis and phytochrome) operate in plants.

156
Q

Some examples of blue-light responses are

A

Phototropism
Stomatal movement
Chloroplast relocation within cells
Inhibition of hypocotyl elongation

157
Q

Characteristics of blue-light responses

A

Blue-light responses can be distinguished from the photosynthesis because any photosynthesis related response occurs both in blue- and red-light; however, blue-light response is not initiated by red-light.

Blue-light responses can be distinguished from the phytochrome because the blue-light responses do not show red/far-red reversibility.

Phototropism, stomatal movement, and chloroplast relocation do not show reversibility and do not respond to red-light.

Action spectra of blue-light responses show “three-finger” patterns.

158
Q

Three major blue-light receptors are:

A
  1. Crytochrome
  2. Phototropin
  3. Zeaxanthin
159
Q

Crytochrome

A

HY4 gene isolated from the hy4 mutant was not phytochrome. -> named as cryptochrome.

74-kDa protein which displays significant sequence homology to microbial DNA photolyase – an ancient protein on earth!

In bacteria, photolyase is activated by blue-light and repairs the UV-damaged DNA (pyrimidine dimer).

Both photolyase and crytochrome have two co-factors, flavin adenonucleotide (FAD) and pterin.

Cryptochrome does not show any DNA-repairing activity.

Cryptochrome is present in nucleus (no evidence for cytosol-nucleus shuttle like phytochome)

Cryptochrome has an extended domain at its C-terminus, which is absent in photolyase.

The C-terminal domain acts as a signal transducer.

Cryptochrome is involved in the regulation of anthocyanidin biosynthesis and inhibition of hypocotyl.

160
Q

Phototropin

A

One Arabidopsis mutant lacks a phototropic response but sill has normal blue-light stimulated inhibition of hypocotyl. On the other hand, hy4 mutant (a known Arabidopsis cryptochrome mutant) has the converse phenotype under blue-light.

Molecular cloning of the mutated gene showed that it encodes a new gene, which was named as “Phototropin”.

N-terminal half has a Flavin mononucleotide (FMN)-binding site. Experiments showed that FMN is covalently bound to a specific cysteine residue by blue-light (see Figure).

N-terminus has light-oxygen-voltage (LOV) domain and C-terminus has a serine/threonine kinase domain.
Phototropin regulates “phototropic response” and “chloroplast movement”.

It localizes on plasma membrane!.

LOV2 domain is responsible for kinase activation, and the phosphorylation status of phototropin determines its activity (Uncaged Model).

Arabidopsis has Phototropin 1 and 2 (Phot1 and Phot2).

phot1/pho2 double-mutant lack both the avoidance and accumulation responses.

Chloroplast Unusual Positioning 1 (CHUP1) mutant failed proper chloroplast movement.

CHUP1 has F-actin-binding activities.

161
Q

Zeaxanthin

A

Photosynthesis, phytochrome, cryptochrome, and phototropin showed “no or partial” influence on stomata movement.

One Arabidopsis mutant (npq1) that has a lesion in the enzyme converting violaxanthin to zeaxanthin in chloroplast, and stomata cells from this mutant lacked the blue-light response! -> Serendipitous discovery.

Very close correlation between stomata opening and zeaxanthin amount (A).

Absorption spectra of zeaxanthin = action spectra of blue-light response (C).

In detached stomata cells, blue-light sensitive is proportional to zeaxanthin amount (A + B).

Inhibitor (DTT, dithiothreitol) for zeaxanthin-forming enzyme can abolish stomata opening by blue-light.

Blue-Green reversibility of stomata opening was observed!

Action spectra for blue light-stimulated stomatal opening and for its reversal by green-light are similar.

Three-finger pattern but ~90 nm shift.

Similar absorption shifts have been observed upon isomerization of various carotenoids in protein environments

Zeaxanthin is also known to be isomerized by light.

A specific zeaxanthin/protein complex for blue/green photo-reversibility has not been identified.

However, orange-carotenoid protein (OCP) provides a hint on blue-light receptor.

OCP is a 35-kDa protein that has a non-covalently bound carotenoid, 3’-hydroxyechinenone.

The blue-light converts the dark-form of OCP to light-form of OCP.

Zeaxanthin-bound protein is likely to be converted by blue-light to a physiologically active form (green-light absorbing form). Green-light will convert the active form to inactive blue-light absorbing form. What is this protein?

162
Q

What may inform plants of unfavorable conditions for photosynthesis

A

Green light

163
Q

H+-ATPase pump regulation after recieving signals from zeaxanthin-protein

A

Default status of the H+-ATPase pump is “locked” condition by its C-terminal domain (auto-inhibitory).

Removal of C-terminus by protease makes the pump “constitutively active”.

Upon blue-light irradiation, the pump’s C-terminus is phosphorylated.

Upon phosphorylation, the pump shows low Km value and high Kcat (turnover) value.

Phosphorylated domain is recognized (bound) by 14-3-3- protein. 14-3-3 protein is a ubiquitous regulatory protein.

164
Q

What is an essential co-factor of blue-light sesing protein which reguklates stomata opening and closing

A

zeaxanthin

165
Q

Quick facts about cryptochrome

A

in nucleus, hypocotyl inhibition (hy4 mutant) and anthocyanin biosynthesis.

166
Q

Quick facts about phototropin

A

on the plasma-membrane, phototropic response, chloroplast movement

167
Q

Quick facts about Zeaxanthin (carotenoids)

A

in the chloroplast, stomata movement (opening and closure).

168
Q

It is believed that zeaxanthin and meso-xanthin in the macula function to

A

block blue light from reaching the underlying structures in the retina, thereby reducing the risk of light-induced oxidative damage that could lead to macular degeneration (AMD).”

169
Q

What are Nitogen firtilizers made from?

A

Ammonia (NH3)

170
Q

How is the ammonia for nitrogen fertilizers produced?

A

Haber-Bosch process

171
Q

WHat is the Haber-Bosch process

A

an artificial nitrogen fixation process and is the main industrial procedure for the production of ammonia today.

Reaction equation: N2 + 3H2 → 2NH3

172
Q

What is the source of nitrogen in the Haber-Bosch process

A

Atmospheric nitrogen

173
Q

What is the source of hydrogen in the Haber-Bosch process

A

Methabe from natural gas

174
Q

The most popular phosphate-containing minerals are referred to collectively as

A

Phosphate rock

175
Q

How are the minerals in phosphate rock converted to water soluble phosphate salts

A

By treatment with sulphuric acid

176
Q

Is phosphate rock finite

A

Yes

177
Q

What used to be used for phosphate fertilizer in US, 1870

A

Bison skulls

178
Q

What is used to manufacture phosphate fertilizers

A

Phosphate rock

179
Q

What country is #1 for phosphate rock reserve

A

Morocco

180
Q

WHat was potassium traditionally prepared from?

A

Pot ash

181
Q

Potash became the term widely applied to naturally occurring potassium _________ and the commercial product derived from them.

A

Mineral salts

182
Q

Potash Corporation of Saskatchewan Inc.

A

World’s largest potash producer, started by Sask. provincial government and privatized in 1989-1990 with mines in Patience Lake, Cory, Allan, Lanigan and Rocanville Sask. and Sussex, N.B.

183
Q

Mechanism of stomatal opening observation 1

A

Blue-light influences stomatal opening

Photosynthesis can be saturated by illumination of red-light

A rapid stomatal opening was observed, and its action spectrum showed a three-finger pattern, which are different from photosynthesis action spectrum.

184
Q

Mechanism of stomatal opening observation 2

A

Stomata protoplasts swell by blue-light

Irradiation of blue-light on stomata protoplasts causes swelling of the protoplasts by gaining a high osmatic pressure.

pH values of the medium containing the stomata protoplasts markedly decrease when protoplasts were irradiated by blue-light. -> Blue-light induces acidification.

185
Q

A proplast is

A

A plant cell without a cell wall

186
Q

What. isthe degree of acidifcation proportional to

A

the amount of photons

187
Q

What kind of treatment abolishes cell swellings

A

Orthovanadate (H+-ATPase inhibitor)

188
Q

How can electric current be measured?

A

Patch-clamp methods

189
Q

What activates H+-ATPase and CCCP

A

Fusicoccin

190
Q

What chemivals can be used to modulate proton gradients in stomata cells

A

H+-ATPase and CCCP (cyanide m-chlorophenylhydrazone)

191
Q

What is a primary response by blue-light

A

Proton gradient

192
Q

___ and ___ are taken up by ion channels

A

K+ and Cl-

193
Q

A series of subsequent secondary reactions help increase osmotic pressure of stomata cells.

A

Potassium (K+) and counter ion (Cl-) are taken up by ion channels (step 1).

Malate (counter ion) is also produced by the hydrolysis of starch in chloroplast (step 1).
Accumulation of sucrose by starch hydrolysis (step 2).

De novo synthesis of sucrose by photosynthesis (step 3).

194
Q

What else is also produced by the hydrolysis of starch in chloroplast

A

Malate (counter ion)

195
Q

Accumulation of ____ by starch hydrolysis

A

Sucrose

196
Q

De novo synthesis of ______ by photosynthesis

A

Sucrose

197
Q

How are the stomata closed upon drought stress?

A

The stress hormone, ABA, concentration increases under drought conditions. (we learned the role of ABA).

ABA binds to the receptor, and derepression occurs (we learned that PP2C is a major negative regulator).

Ca2+ is a key signaling messenger.

Ion efflux is promoted ; Ion influx is inhibited. These are essentially the physiological response, reversal to those in stomata opening.

Stomata closure.

198
Q

Summary of stomatal biology

A

Blue-light relays a signal, which is distinct from photosynthetic and red/far-red signaling.
An action spectrum of stomata movement (opening/closure) is unique- three-finger pattern.

Blue-light activates “H+-ATPase” proton pumps on the plasma-membrane of stomata cells.

A number of secondary responses occur to build solutes and ions inside stomata cells.

Increase osmotic pressure, followed by water uptake and stomata opening.

Entirely reversal responses occur by drought stress, mediated by ABA and Ca2+ signaling, to close stomata.

199
Q

Whaty is a unique feature among angiosperms

A

Double fertilization

200
Q

What is doubl fertilization

A

Along with the fusion of a sperm with the egg to create a zygote (chromosome = 2n), a second male gamete fuses with the polar nuclei in the embryo sac to generate the endosperm tissue

201
Q

Pattern Formation during Arabidopsis embryogenesis

A

Straight-forward observation of cell differentiation starting from zygote using microscope

202
Q

What are marker proteins useful for?

A

Tracing gene expression and protein localization.

203
Q

What is the only hormone displaying a concentration gradient in plant = morphogen

A

Auxin

204
Q

Auxin in 2-cell stage

A

Maximum auxin at top

205
Q

Auxin in globular embryo

A

Maximum axin at the base

206
Q

Auxin in early heart stage

A

Maximum at base and in top L/R corners

207
Q

Does Auxin have polarity

A

Yes

208
Q

What does not control the direction of auxin flow

A

gravity

209
Q

What is a morphogen

A

Signaling molecules (proteins or otherwise) that act over long distances to induce responses in cells based on the concentration

210
Q

WHat property is an important criterterion for auxin being a morphogen

A

polarity

211
Q

How can plants achieve the “polar transport of auxin”?

A

Chemiosmotic model of polar auxin transport

212
Q

Chemiosmotic model of polar auxin transport

A

IAA enters the cell
Cell wall has an acidic pH maintained by H+ ATPase
Cytosol has neutral pH (the anionic form IAA- dominates
The anions exit the cell via auxin anion efflux carriers

213
Q

What is Aux1

A

influx pump (more specifically 2H+-IAA- permease that co-transporting two protons and one IAA).

214
Q

What is phyllotaxy

A

The pattern of leaf formation from the shoot in plants, and scientists were interested in the leaf pattern formations – Use Arabidopsis as a model to study phyllotaxy.

215
Q

What happens to the stem and organs in Arabidopsis pin1 mutant

A

The stem grows normally but no lateral organs are formed.

216
Q

What is the The PIN family of proteins

A

auxin efflux pump. The name PIN was derived from the pin-shaped influorescence formed by pin1 mutation.

217
Q

How many PIN genes have ben identified

A

Five PIN genes have been identified in Arabidopsis (PIN1,2,3,4, and 7), but PIN1 is the most important one.

218
Q

What does auxin transport induce?

A

Auxin transport induces floral and leaf bud (primordial) development (directly influencing phyllotaxy)

219
Q

An additional family of efflux pump help PINs desrcibe some of their features

A

These are ATP-binding Cassette (ABC) integral membrane protein – ABC transporter.

“B-subfamily” of ABC transporter is responsible for this efflux, and thus called as ABCB.

They are sometime called “P-glycoproteins”.
Energy-requiring and consumes ATP.

Independent pump and synergistic pump functions.

220
Q

Do humans have these ATP-binding Cassette (ABC) integral membrane protein – ABC transporters?

A

Yes
DRug efflux transporters
Role in tissue protection and detoxification
Multidrug resistance in Cancer

221
Q

Testable hypothesis: Auxin concentration gradient is generated by dynamic and sophisticated distributions of transporters.

A
  1. Influx - Proton:Auxin co-transporter & passive diffusion
  2. Efflux – PIN protein (Auxin transporter) + ABC transporter (B-family)

The most dramatic evidence for this hypothesis comes from the studies of PIN protein localization.

222
Q

Remarkable plasticity of plant development is attributed to specialized tissues called

A

Mesistem

223
Q

Meristem is a group of cells that

A

Retain the capacity to proliferate and maintain “cells whose fates were undetermined”.

224
Q

Two major meristem cells are

A

root meristem (RAM) and shoot meristem (SAM).

225
Q

What are initials

A

a group of slowly dividing and undetermined cells in RAM and SAM. Their descendants are displaced away by polarized pattern of cell division and take on various differentiated cell fates.

226
Q

Quiescent center is chracterized by

A

no cell division and elongation

227
Q

Central cylinder of the root cap

A

Columella

228
Q

“Initials” in Shoot Meristem cells by zone

A

CZ (central zone) - equivalent to QC in RAM
PZ (peripheral zone) – leaf primordial
RZ (rib zone) – stem tissue

229
Q

“Initials” in Shoot Meristem cells by layer

A

L1 (Layer 1) – epidermis
L2 and L3 (Layer 2 and 3) – internal tissue

230
Q

Subcellular localizations of PIN protein in Arabidopsis

Central region of RAM where cells divide more slowly than surrounding cells, or do not divide at all

A

QC

231
Q

The Quiescent Center (QC) has the highest level of

A

Auxin

232
Q

T/F Different PIN family protein mediate auxin efflux in different tissues.

A

T
They regulate distinct cell patterning genes in different tissues.

233
Q

Cell-type specific presence of PIN and ABCB proteins specify the

A

directional auxin flow in plants.

234
Q

seeds are grouped into two classes:

A

endospermic or non-endospermic (absence and presence of endosperm at seed maturity).

235
Q

Sources for germinations:

A

endosperm vs. perisperm & cotyledons

236
Q

WHat are some of the major nutrients in seeds, stored for germination

A

Starch, oil, and proteins

237
Q

What are some of the major factors that promote germination

A

Water, oxygen, and temperature

238
Q

Seeds may not germinate even though favorable conditions are given. This is called

A

Seed dormancy

239
Q

Seed coats can cause dormancy by limiting water permeability (mechanical scarification), physically constraining the redicle growth, interfering with gas exchange, or providing germination inhibitors. This is chracteristic of?

A

Coat imposed dormancy

240
Q

Inherent nature of plants (is not caused by seed coats). e.g. small undifferentiated embryo of parasitic plants.

A

Embryo dormancy

241
Q

Release from dormancy is dependent on

A

Hormonal balance between ABA and GA

242
Q

Light signal (e.g. Red/Far-red ratio) is sometime a critical decision-maker for ______. Often small seeds are far more sensitive to light condition.

A

Breaking dormancy

243
Q

What is stratification

A

chilling seeds to break dormancy. It is a common agricultural practic

244
Q

Various chemicals can break dormancy

A

(e.g., chemicals in smoke or 1M HCl)

245
Q

Seeed gernination phase 1: imbibition

A

a process of water uptake by seeds (water potential)

246
Q

What stage of seed germination do metabolic changes occur in

A

2

247
Q

What stage of seeds germination do developmental progresses occur in

A

3

248
Q

Phase 2 of seed germination

A

Metabolic changes (Mobilization of stored reserves) are mediated by hormone signaling. GA is the most important hormone in germination

249
Q

Phase 3 of germination

A

Seed growth and establishment
Various tropisms and hormone actions are involved

250
Q

Two hypotheses for whether phototropism occurs by auxin break-down or redistribution

A

Auxin may be light sensitive and light could mediate decomposition of auxin on the lighted side.

Auxin could be redistributed to the shaded side. Auxin produced at the tip is transported laterally toward the shaded side.
> Cholodny-Went Model

251
Q

Classical experiments supporting auxin redistribution in phototropism

A

Cholodny-Went hypothesis: lateral movement (asymmetric distribution) of auxin causes tropisms.

252
Q

What does asymmetric distribution of auxin control?

A

Phototropism
Graviation

253
Q

What is gravitropism

A

A coordinated process of differential growth by a plant in response to gravity pulling on it.

254
Q

Physiology of gravitropism and balance

A

The auxin (growth hormone) redistribution occurs by coordinated work of statolith, columella cells (statocytes), and auxin efflux and influx pumps.
Auxin acts as an growth inhibitor in root by an unknown reason.

255
Q

What is a statolith

A

Specialized starch filled plastid

256
Q

What is a columella cell (statocyte)

A

A specialized cell in the root cap

257
Q

Rapid cytosolic alkalization (or apoplast acidification) occurs by

A

Gravi-stimulation

258
Q

Starch-statolith hypothesis

A

How do statocytes sense the sedimenting bodies (statolith)?

259
Q

The Great Famine (or Irish Potato famine) between 1845 and 1852.

A

Potato was introduced to the Ireland in early 1600 from South America, and it became main food for the poor in Ireland in the first decade of 1800

Lack of genetic variability by monoculture – one potato cultivar was grown!

Potato blight was introduced from USA - Phytophthora infestans (Oomycete)
Don’t know the exact number of death, but it is estimated that 1 million (mostly the poor farmers and their families) died during the Great Famine

260
Q

Dutch elm disease

A

eliminated elm trees in America and Europe.

Caused by pathogenic fungi (Ascomycota), which is spread by elm bark beetles.

To prevent the spread of the fungi, elm tree reacts to plug its own xylem tissue with the development of new tissues – eventually it leads to the failure of xylem function.

261
Q

Sources for the plant disease are :

A

virus (mediated by feeding insects), fungi (Ascomycetes and Basidomycetes), Oomycete (it forms a very unique clade, closer to water mold), and bacteria. Although bacteria are common causes for human disease, fungi are major causes of plant disease.

262
Q

Constitutive defense

A
  1. Mechanical barriers
    Surface structures, mineral crystal, thiagmonastic (touch-induced) leaf movement
263
Q

What kind of crystals are present in the vacuoles of many species

A

Calcium oxalate

264
Q

What is the purpose of Calcium oxalate crystals

A

form needle-like structures, called “Raphide”

Harmful to larger herbivores as it can penetrate the soft tissues (throat and gut) in insects.

265
Q

Secondary (or specialized) metabolites

A

Are not the essential metabolic products for “plant growth and development”, but they significantly increase the fitness of plants in real eco-systems, filled with hostile pathogens and insects.

Three major classes are phenolics, terpenoids, and alkaloids

Are often toxic to plants themselves and thus are stored in specialized storage organs – resin duct, trichome, or laticifer

266
Q

Example 1. glucosinolate

A

Plants store toxic secondary metabolite as non-toxic sugar conjugates in vacuoles

In the order of Brassicales, soluble, non-toxic glucosinolate is stored in S-cell (sulfur-rich cells) and myrosinase (a thioglucosidase) is stored in different cells than its substrate (glucosinolate).

When leaves are chewed by insects, enzymes (myrosinase) and substrates (glucosinolate) meet each other, and highly toxic isothiocyanate is produced – mustard bomb!

Isothiocyanate is responsible for the flavors in Mustard, wasabi, radish, brussels sprout

267
Q

Cyanogenic glycosides in sorghum and cassava

A

Upon tissue damage, the sugar group is removed from the cyanogenic glycosides and hydrogen cyanide (HCN) is generated. Cyanide ion inhibits electron transport chain in mitochondria (more specifically block cytochrome c oxidase).

268
Q

Problems of constitutive defense responses:

A

Constitutive defenses always use valuable resources, whether insects are present or not. In a wild eco-system, many different plant species compete to dominate restricted niches, and they have to allocate resources to growth and reproduction too. Constitutive defenses are expensive!

Insects (or other pathogens) can acquire resistance against the defensive chemicals, if they are constitutively exposed to the toxic chemicals (as pathogenic bacteria gain anti-biotic resistance when anti-biotics are inappropriately or unnecessarily used).

Different types of insect attacks – Phloem feeders (aphids and while flies); Cell-content feeders (mites and thrips); Chewing insects (caterpillars).

Plants need sophisticated inducible defense mechanisms for different types of attacks, and at the first place plants need to sense the insect attacks.

269
Q

What are elicitors

A

chemicals (from insects) which trigger defense responses in plants to a wide variety of herbivores and pathogens.

270
Q

Fatty acid amide (fatty acid and amino acid conjugate) in the saliva of larvae of the beet armyworm. Fatty acid backbone [linolenic acid (18:3) and linoleic acid (18:2)] is from plant!

A

Volicitin

271
Q

Sulfated fatty acids isolated only from grasshopper (suborder: Caelifera). Unlike the Volicitin, the fatty acid backbone is unusual structure (irregular number carbon number and trans-configuration double-bond).

A

Caeliferins

272
Q

Insect elicitors (Volicitin and Caeliferin) induce

A

The Ca2+ -mediated signaling and jasmonic acid (JA) biosynthesis in plants

First, cytosolic calcium concentration rapidly increases upon treating plants with elicitors. Calcium is used as a secondary massager to activate calmodulin proteins, calcium-binding proteins, and calcium-binding kinase.

Second, octadecanoid pathway is activated to synthesize jasmomic acid (JA), which in turn activates a wide array of defense responses. JA can also be considered as a hormone in plant-insect interactions

SImilar to prostaglandin

273
Q

Biosynthesis and physiological roles of prostaglandin in humans

A

Constriction and dilation in vascular smooth muscle.
Aggregation of platelets.
Induce labor.
Regulate inflammation.
Act on the thermoregulatory center in brain.

274
Q

What induces anti-digestive proteins in plants

A

JA

275
Q

JA initiates the synthesis of defense-related proteins that inhibit

A

Herbivore digestions

276
Q

“α-amylase inhibitor” proteins are synthesized when

A

plants are treated with JA. This enzyme inhibitor from plants inactivate “α-amylase” in insect digestive tracks.

277
Q

“Lectin” proteins are synthesized in response to

A

JA
This protein interfere with nutrient absorption in insect digestive track.

278
Q

“Proteinase inhibitor” proteins are synthesized in response to

A

JA
This protein tightly binds to key protein-hydrolyzing enzymes, trypsin and chymotrypsin.

279
Q

Gene-for–Gene (hypothesis) model by Dr. Flor in 1940s

A

Defense against virus, fungi, oomycetes, and bacteria

280
Q

Resistant gene in plant

A

R

281
Q

Avirurence gene in pathogens (bacteria, fungi, and virus)

A

AVR

282
Q

Where do microbial pathogens invade plants through?

A

Natural openings, such as stomata and hydathode

283
Q

T/F wounding sites can be infected by microbial pathogens

A

T

284
Q

Fungi and oomycetes can release cell-wall degrading enzymes to actively penetrate into the plant tissues (using unique structures, such as:

A

Appressorium, infection peg, haustorium, see next slide)

285
Q

Necrotrophic pathogens:

A

kill plants by releasing cell wall-degrading enzymes, toxins. Then they use the dead plant tissues as a food source.

286
Q

Biotrophic pathogens:

A

causes minimal cell damages on plants and use nutrients provided by the infected plant tissues

287
Q

Hemibiotropic pathogens:

A

Keep the plants alive initially but they kill plants at the later stage of infections.

288
Q

What are effectors?

A

Molecules (produced from the pathogens) that change the plant’s structure, metabolism, or hormone regulation to the advantage of the pathogens. They can be enzymes, toxin, and growth regulator

289
Q

Types of effectors from pathogens

A

Enzymes: cell wall-degrading enzymes such as cutinase, cellulase, xylanase, pectinase, polygalacturonase.

Toxins: HC toxin from Cochliobolus carbonum inhibit the histone deacetylation in plants; Fucicoccin from Fusicoccum amygdali binds to H+-ATPase and irreversibly activate this transporter on the membrane.

Hormone: Gibberella fujikuroi synthesizes gibberellic acid to cause foolish seedling disease in rice.

290
Q

Pkants deploy two layers of immune systems :

A

MAMP (microbe associated molecular patterns)-triggered immunity and effector-triggered immunity.

Pattern recognition receptors (PRR) on the cell surface play important roles.
Two types of PRRs are “MAMP” released from pathogens and “DAMP” (damage-associated molecular patterns) released from plants.

291
Q

Examples of MAMPs

A

chitin from fungi and flagella from bacteria

292
Q

Example of DAMP

A

is systemin in tomato or cell wall-components

293
Q

MAMP and DAMP are recognized by

A

receptor-like kinase (RLK) or receptor-like protein (RLP)

294
Q

Pathogenic bacteria can bypass the surface-deployed detection systems by

A

Directly injecting various effectors into the cytoplasm of plant cells.

295
Q

Plants have a secondary immune system to detect those effectors in cytoplasm using

A

soluble nucleotide binding site-leucine rich repeat (NBS-LRR) receptors – or R (resistant) genes

296
Q

Specificity of disease resistant in plant is determined by a specific ______ in pathogen and a specific ________ in plant.

A

Effector and R gene

297
Q

Guard hypothesis for R gene signaling during plant defense against pathogens

A

Scientists had difficulties in finding evidence for direct interaction of R (e.g., NBS-LRR receptor) and Avr (effector). What is the target of effector then?

It is proposed that plant uses the target protein as a decoy to recognize the presence of effector. There are some experimental data to support this hypothesis.

Once virulence protein bound on target protein in plant to weaken defense, but now plants use the target protein as a decoy to sense the attack of pathogen.

298
Q

What’s the result of Avr-R interaction?

A

Hypersensitive responses in plant

299
Q

Essential components for hypersensitive response

A

“Nitric oxide (NO)” and “reactive oxygen species (ROS)”

300
Q

Disease resistant mutants for Gene-for–Gene (hypothesis) are:

A

R/R or R/r and AVR/avr and AVR/AVR

All the other mutants are susceptible to disease

301
Q

Plant pathology and disease monitoring system

A
  • University or government laboratories
  • Database for pathogens (Molecular ID)
  • Genetic resources (thousands of cultivars of each crop)
302
Q

In primary cell walls, _________ microfibrils are embedded in a hydrated matrix of non-cellulosic polysaccharides (sugars) and a small amount of structural protein.

A

cellulose

303
Q

Primary cell walls are formed by

A

growing cells

304
Q

Secondary cell walls are formed

A

after cell growth stops between the primary cell walls and the plasma membrane.

305
Q

What is the most important component in the secondary cell walls

A

Lignin

306
Q

Components of primary cell walls

Cell wall polysaccharides are classified into three groups.

A

Cellulose
Hemicellulose
Pectin

307
Q

Additional non-carbohydrate components

A

Lignin
Structural proteins

308
Q

Main components of cell walls are

A

Sugars

309
Q

Cellulose

A

The most abundant bio-polymers on earth (the second most abundant one is lignin).

1.5×1012tons of the total annual biomass production. Cellulose is considered an almost inexhaustible source of raw material. 1x109 tons of celluloses = 1/3 of transportation fuel in USA.

A linear chain of several thousands of β(1→4) linked β-D-glucose. Cellobiose is the repeating units in cellulose.

Tightly packed to form a microfibril by hydrogen bonds.

Micrometer (µm) length and 1-10 nanometer (nm) width.

Each cellulose chain in microfibrils is composed of thousands of monomers (2,000 – 25,000).

310
Q

Scanning Electron Microscopic (SEM) data

A

Focused electron beams are used to examine surface topology of the samples at nm resolution.

311
Q

Biosynthetic model for cellulose synthesis on the plasma membrane

A

Cellulose synthases span the plasma membrane with their catalytic site on the cytoplasmic side.

Abundant carbon source, sucrose, is cleaved to glucose and fructose by sucrose synthase.

Glucose is activated to uridine diphosphate D-glucose (UDP-glucose)

312
Q

Hemicellulose

A

Hemicelluloses are primarily made of five carbon sugars.

Different from cellulose, they have side-chains which interfere the crystalline formation of hemicellulose molecules.

Xyloglucan and glucuronoarabinoxylan are two common hemicelluloses. Examine these structures!

Hemicelluloses are usually longer than cellulose microfibrils, and they cross-link cellulose microfibrils on cell walls.

313
Q

Pectin

A

Hydrophilic gel-forming components.

Pectin is also composed of heterogeneous polysaccharides but it is different from hemicellulose in that..…

Galacturonic acids form the main backbone of pectin (galacturonan)

Pectins are hydrophilic gel-forming components of the matrix.

Ca2+ ions help pectin form a network by ionic bonds.

314
Q

Matrix polymers are synthesized in the _____and secreted via _____

A

Golgi apparatus, vesicles

315
Q

Cell wall assembly

A

Synthesis -> deposition -> assembly -> modification

316
Q

Self-assembly model:

A

Isolated celluloses can be dissolved in strong solvents, and stable fiber can be formed spontaneously - Manufacturing of Rayon (cellulose fiber)

317
Q

Enzyme-mediated assembly model:

A

XET enzyme can cut xyloglucan and add a new xyloglucan molecules in vitro

318
Q

Lignin is more abundant in

A

Secondary cell walls

319
Q

Overall, three major constituents of all cell walls (primary + secondary) are:

A

cellulose, hemicellulose, and lignin

320
Q

Plant cells sometimes continue to synthesize a ______ after wall expansion ceases.

A

Secondary wall

321
Q

The secondary cell walls have all cell wall components, but it becomes more strengthened by

A

Lignin

322
Q

Two important considerations for cell wall expandability are:

A

How can directional growth of plant cells occur?
How can rigid cell walls expand?

323
Q

Microtubules dictate the orientation of newly deposited cellulose microfibrils.

A

Tubulin is a subunit of cytoskeletal structure microtubules, and oryzalin depolymerize microtubules.

Treatment of oryzalin on root tip cells causes non-directional enlargement.

Immunofluorescent signals of CesA overlaps with microtubule subcellular locations.

Microtubules guide the deposition of CesA inside the cells.

324
Q

Does the lignin biosynthesis randomly occur in plants?

A

Casparian strip model

CASP1 protein organizes membrane proteins at the Casparian strip.

325
Q

Acid growth hypothesis

A

To change shape, plant cells must control the direction and rate of cell wall expansion.

Plants need to deposit cellulose in a biased orientation and selectively loosen the bonding between cell wall polymers.

“Creep” refers to an irreversible extension of cell walls, which occurs by slippage of cell wall polymers relative to one another.

Two important observations relevant to cell wall expansion are 1) cell wall loosening is enhanced at acidic pH and 2) drug fusicoccin treatment on plants enhanced cell wall loosening. Fusicoccin is known to activate H+-ATPase on plasma membrane (e.g., H+-ATPase agonist).

An “extensometer” can be used experimentally to measure cell wall expandability.

Expansin proteins play an important role in cell wall expansion.

326
Q

Applications of acid growth hypothesis

A

Cotton (fibre is pure cellulose)
Lignocellulosic biofuel

PLBI 403 (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions