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CSC3201 - Plant and Crop Physiology I > CSC3201 - Plant and Crop Physiology I > Flashcards

CSC3201 - Plant and Crop Physiology I Flashcards

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1
Q

What are the five recognized groups of plant hormones?

A
  • Auxins
  • Gibberellins
  • Cytokinins
  • Abscisic acid
  • Ethylene
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2
Q

What are plant hormones?

A

Naturally occurring, organic substances that at low concentration exert a profound influence on physiological processes.

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3
Q

Where are auxins primarily present in plants?

A

In meristematic regions, apical buds of growing stems, and germinating seeds.

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4
Q

From which amino acid are auxin molecules derived?

A

Tryptophan

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5
Q

What are gibberellins biosynthetically related to?

A

Carotenoids

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6
Q

What is the primary role of abscisic acid in plants?

A

Regulating seed germination, inducing storage protein synthesis, and modulating water stress.

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7
Q

What is ethylene?

A

A gaseous hydrocarbon not required for normal vegetative growth.

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8
Q

What physiological function do auxins serve in plants?

A

Stimulate cell enlargement.

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9
Q

What hypothesis explains how auxin activates cell enlargement?

A

The acid-growth hypothesis.

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10
Q

What do small auxin upregulated RNAs (SAUR) encode?

A

Short, relatively unstable transcripts.

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11
Q

What is polar transport in the context of auxins?

A

The preferential movement of auxins in one direction.

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12
Q

What concentration of auxins promotes root elongation?

A

Low concentrations.

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13
Q

What is apical dominance in relation to auxins?

A

It is the suppression of axillary buds by the dominant apical bud due to auxin gradients.

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14
Q

Where are gibberellins produced in plants?

A

In developing seeds and fruits, young leaves, and elongating shoots.

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15
Q

What effect do gibberellins have on seed dormancy?

A

They can overcome seed and bud dormancy.

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16
Q

How do gibberellins influence flowering?

A

They can substitute for long day requirements and vernalization.

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17
Q

What role do gibberellins play in seed storage cells?

A

Stimulate aleurone to manufacture hydrolytic enzymes for digesting food reserves.

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18
Q

What commercial application do gibberellins have?

A

Increasing the size of Thompson seedless grapes.

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19
Q

What is the effect of cytokinins on cell division?

A

Increases cytokinesis and rapid multiplication of cells.

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20
Q

What happens if the cytokinin-to-auxin ratio is high?

A

Meristematic cells are produced in the callus.

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21
Q

What is one effect of cytokinins on aging leaves?

A

Prevention of senescence.

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22
Q

How do cytokinins influence lateral bud development?

A

Promote growth of buds that are influenced by apical dominance.

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23
Q

What happens to chloroplast development in seedlings grown in the dark?

A

Proplastids do not develop into chloroplasts.

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24
Q

What is the chemical structure of ethylene?

A

H2C=CH2

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25
What effect does ethylene have in waterlogged soils?
Synthesis of cellulase causing degradation of cell walls.
26
What is one effect of ethylene on flowers?
Promotes senescence of flowers.
27
What are polyamines?
Compounds containing two or more amino groups.
28
What is the primary role of abscisic acid?
It acts as a stress hormone.
29
How does abscisic acid signal water stress in plants?
Transported from roots to leaves to signal stomate closure.
30
What triggers the synthesis of abscisic acid in response to water stress?
Loss of turgor in leaves.
31
What effect does salt stress have on plants?
Causes production of new proteins such as osmotin.
32
What activates certain nuclear genes leading to enhanced ABA synthesis?
Loss of turgor allows the transporting of Ca2+ into the cell at an increased rate. ## Footnote Ca2+ and phosphoinositols act in the signal-transduction chain to activate genes needed for ABA synthesis.
33
What stress conditions activate the formation of ABA in plants?
Salt and cold stress ## Footnote Cold stress protects plants from cold through a series of reactions.
34
What is osmotin and its role in plants?
Osmotin is a protein produced in response to salt stress that helps control salt stress in plants. ## Footnote Observed in tobacco plants.
35
How is ABA linked to seed development?
ABA is linked to normal maturation of seeds and prevention of precocious germination. ## Footnote Increased ABA controls deposition of reserve proteins in seeds.
36
What hormone induces bud dormancy in plants?
Abscisic Acid (ABA) ## Footnote Synthesized in leaves that detect day length and translocated to buds.
37
What effect does exogenous ABA have on seed germination?
Exogenous ABA is an inhibitor of seed germination in many species.
38
How does ABA influence abscission in plants?
ABA causes premature senescence of cells in the organ that is shed, provoking a rise in ethylene production.
39
Define tropism in plants.
A tropism is a growth toward or away from a stimulus.
40
What is the difference between tropisms and nastic movements?
Tropisms are directional growth responses to stimuli, while nastic movements are responses that are not dependent on the direction of the stimulus.
41
What is phototropism?
Phototropism is the directional growth of an organism in response to light.
42
What role do photoreceptors play in phototropism?
Photoreceptors detect light and direct auxins to the shaded side of the stem, causing differential growth.
43
What is the result of auxin accumulation on the shaded side of a plant stem?
Cells elongate at a greater rate on the shaded side, causing the stem to curve toward the light.
44
What is heliotropism?
Heliotropism is the ability of certain plant structures to follow the path of the sun.
45
What is thigmotropism?
Thigmotropism is the growth of plants in response to touch or contact with a solid object.
46
What is gravitropism?
Gravitropism is growth in response to gravity.
47
What is the role of amyloplasts in gravitropism?
Amyloplasts sediment in response to gravity, helping roots sense the direction of gravitational pull.
48
What happens to auxins in roots when a plant is placed horizontally?
Auxins accumulate on the lower side of the roots, resulting in slower growth and downward curvature.
49
What is hydrotropism?
Hydrotropism is directional growth in response to water concentrations.
50
How do roots exhibit hydrotropism?
Roots grow toward the direction of water due to differential growth induced by ABA.
51
What types of tropism are less commonly discussed?
Thermotropism and chemotropism. ## Footnote Thermotropism is growth in response to temperature changes, while chemotropism is growth in response to chemicals.
52
What is nyctinasty?
Nyctinasty is a movement controlled by interactions between the environment and the biological clock, often seen in leaves that change position between day and night.
53
What occurs in the pulvinus during nyctinasty?
Motor cells in the extensor region lose turgor during closure, while those in the flexor region gain turgor.
54
What physiological changes accompany leaflet closing in nyctinasty?
Loss of K+ from the ventral side and absorption of K+ on the dorsal side.
55
What are nastic movements?
Movements that occur in response to environmental stimuli but are not dependent on the direction of the stimulus ## Footnote Examples include nyctinasty, hydronasty, and thigmonasty.
56
What are nyctinasty movements sensitive to?
Sensitive to blue light, the physiological status of phytochrome, and endogenous rhythms.
57
What ions are redistributed in nyctinasty movements?
Potassium ions (K+) and chloride ions (Cl-).
58
What causes the closing of leaflets in nyctinasty?
Loss of K+ from the ventral side and absorption of K+ on the dorsal side.
59
What cells are involved in hydronasty?
Bulliform cells.
60
What triggers the folding and rolling of leaves in hydronasty?
Loss of turgor pressure in bulliform cells due to water stress.
61
What is thigmonasty?
Movements that result from touch or mechanical stimulation.
62
What is an example of a plant exhibiting thigmonasty?
Mimosa.
63
What substance elicits electrical responses in thigmonasty?
Turgorin.
64
What is the function of action potentials in the Venus flytrap?
To cause the lobes to snap shut when triggered by an insect.
65
What role do hydrogen ions play in the Venus flytrap's response?
They loosen the cell walls, allowing for rapid absorption of water and causing the trap to shut.
66
What is thigmomorphogenesis?
Developmental effects of mechanical stimulation, causing shorter and stockier plants.
67
What is seismomorphogenesis?
Changes in plant response to shaking, resulting in shorter and stockier plants.
68
What is photomorphogenesis?
The development of plants in response to light.
69
What is phytochrome?
A homodimer of two identical polypeptides that absorbs light.
70
What is the molecular weight of each phytochrome polypeptide?
About 120 kDa.
71
What type of light does phytochrome absorb most strongly?
Red and far-red light.
72
What is photoperiodism?
An organism's capacity to measure the proportion of daylength in a 24-hour period.
73
What are short-day plants?
Plants that flower when daylength is shorter than a critical maximum.
74
What are long-day plants?
Plants that flower in response to daylengths longer than a critical minimum.
75
What are day-neutral plants?
Plants that flower irrespective of daylength.
76
What is the critical importance of the dark period in photoperiodism?
The dark period is more important than the light period for flowering.
77
What is evocation in plants?
The change at the meristem from vegetative to reproductive growth.
78
What is vernalization?
The low-temperature promotion of flowering in certain plants.
79
What is the temperature range for effective vernalization in some species?
-5°C to +15°C.
80
What is the role of gibberellins in relation to vernalization?
They increase in response to low temperatures and can substitute for cold requirements.
81
What is a characteristic growth form of biennials before flowering?
Rosette form with short internodes.
82
What happens to biennials after exposure to winter?
They undergo bolting and flowering in the next growing season.

CSC3201 - Plant and Crop Physiology I (1 decks)

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