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BIOS TEST 3 > Plant Hormones and Sensory Systems > Flashcards

Plant Hormones and Sensory Systems Flashcards

1
Q

Hormones in Plants

A
  • Hormones travel throughout the body via the vascular tissues (xylem + phloem) and cell-to-cell (plasmodesmata)
  • potentially every plant cell can produce plant hormones
  • plants DO NOT have specialized hormone-producing glands like animals
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2
Q

Hormone Roles in Plants

A

Hormones regulate a variety of plant behaviors to different stimuli/environmental conditions; hormones:
1. initiate and regulate plant behaviors
2. provoke these responses and pathways that regulate the responses

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3
Q

Auxin

A

the “youth” hormone and master growth regulator
Tissues with high auxin are areas of new growth and do not exhibit signs of aging
- Responsible for cell elongation in phototropism + gravitropism, apical dominance, and inhibition of abscission
- synthetic auxin is used as a rooting hormone to promote root growth on cuttings + detached leaves

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4
Q

Senescence

A

ageing

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5
Q

Abscission

A

lead falling in plants

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6
Q

Cytokinin

A

the “cell division” hormone
- promotes CYTOKINESIS (cell division)
- abundant in growing tissues, such as roots, embryos, and fruits, where cell division is occurring
- INFLUENCED BY AUXIN (EX: apical dominance results from a balance of auxins that inhibit lateral buds and cytokinin that promote bushier growth)

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7
Q

Gibberellin (GAs)

A

the “growth” hormones; stem, fruit, and seed growth
- Stimulate shoot elongation, seed germination, and fruit + flower maturation
- synthesized in the root and stem apical meristems, young leaves, and seed embryos
- breaks dormancy in the seeds of plants that require exposure to cold or light to germinate

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8
Q

Abscisic Acid (ABA)

A

the “dormancy” hormone
- accumulates as a response to stressful environmental conditions (dehydration, cold temps, or short day lengths)
- its activity COUNTERACTS THE GROWTH PROMOTING EFFECT OF GAS AND AUXINS
- causes abscission of leaves, inhibits stem elongation, induces dormancy in buds and seeds, and closes stomata in short-term droughts

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9
Q

Ethylene

A

the “aging” hormone; lead abscission, flower wilting, and lead abscission
- aging tissues and nodes of stems produce ethylene

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10
Q

Plant Responses to Stimuli

A
  • Light: Phototropism + Germination
  • Gravity: Gravitropism
  • Growth
  • Water or Water Stress
  • Touch: Thigmotropism
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11
Q

Plant Response to Light

A
  • Plants can detect and respond to BLUE, RED, and FAR-RED light
  • Different wavelengths are detected by different photoreceptors (protein + Chromophore = CHROMOPROTEIN)
  • Behaviors regulated by light include phototropism, stem elongation, germination, and photoperiodism
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12
Q

Phototropism

A

movement toward/away from light; movement in response to light
- light is detected by the tip of the plant (apical meristem)
- the response occurs when the signal travels from the apical meristem to the base of the plant causing BENDING
- the detection of light in the apical meristem occurs via PHOTOROPINS (phot1 + phot2), which detect BLUE LIGHT
- Auxin promotes elongation, causing bending

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13
Q

Acid Growth Hypothesis

A

Auxin stimulates cell elongation of the shady side of the stem through the ACID GROWTH HYPOTHESIS:
- auxin causes cells to activate proton pumps, which pumps protons out of the cells and intro the space between the PM and cell wall

the movement of protons into the extracellular space causes:
1. lower pH activates EXPANSIN
2. Sugar movement

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14
Q

Phototropism: Expansin

A

the lower pH activates this, which breaks the links between the cellulose fibers in the cell walls, making them more flexible

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15
Q

Phototropism: Sugar Movement

A

the high concentration of positive ions causes sugars to move into the cell, which creates an osmotic gradient where water moves into the cell causing it to expand

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16
Q

Phototropism Response Summary

A
  • Phototropins Phot1+Phot2 are present in the plant apical meristem
  • When activated by BLUE light, phot 1+2 cause the accumulation of auxin on the shaded side of the plant
    Auxin promotes elongation due to the weakening of the cell wall combined with an influx of water that stretches the cell
  • since the cell expansion only occurs on the shaded side of the stem, the plant bends away from the shade and toward the light
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17
Q

Response to RED light: Growth/Germination

A
  • RED LIGHT PROMOTES STEM ELONGATION; indicates full sun to a plant
  • A far-red light indicates that a plant is being shaded out by another plant
  • unfiltered, full sunlight conditions contain much more red light than far red light
  • PLANTS USE RED VS FAR-RED LIGHT DETECTINO TO GROW AWAY FROM SHADE AND TOWARDS LIGHT
18
Q

Phytochrome

A

the chemo protein responsible for red/far-red light detection; acts like a reversible switch that can absorb either red or far-red light
- Pr (phytochrome red)
- Pfr (phytochrome far-red)

19
Q

Pr

A

capable of absorbing red light (~667 nm)
- phytochrome is in this form when in the dark, causing a seed to not germinate

20
Q

Pfr

A

capable of absorbing far-red light (~730 nm)
- the physiologically active form of the protein; because phytochrome is in the Pfr state after exposure to red light, this means that exposure to red light turns the phytochrome “on”
- in dormancy + germination, this signaling causes the trancription of AMYLASE

21
Q

Pr + Pfr

A
  • when Pr absorbs red light, it is immediately converted to Pfr; when Pfr absorbs far-red light, it is immediately converted back to Pr
  • Exposure the far-red light inhibits phytochrome activity
22
Q

Phytochrome: Plant Growth

A
  • phytochrome stimulates plant growth TOWARD RED LIGHT in combination with the hormones cytokinin and gibberellin
  • cytokinin is only capable of promoting division when auxin is also present, which is only at APICAL MERISTEMS
  • auxin regulates GA levels
23
Q

Phytochrome: Seed Germination

A
  • the seeds of many plants go into dormancy after fertilization to ensure survival - many different signals can trigger germination depending on plant species
  • for many species, this signal is a RED LIGHT, as it provides a signal that the seed is in a good location for cull access to the sun after germination
  • a seed that germinates in shaded areas or too deep underground is likely to die after germination
  • some plant species initiate germination through a light-independent process regulated by GA
24
Q

Amylase

A

breaks down starches stored in a seed into simple sugars, then germination proceeds

25
Gravitropism
ensures that roots grow into the soil and shoots toward sunlight - NEGATIVE: growth of shoot apical tip upward - POSITIVE: growth of roots downward
26
Amyloplasts (AKA Statoliths)
specialized cellular compartments that contain starch granules that move in response to gravity; found in shoots and specialized cells in the root cap - starch granules are heavy and fall to the bottom of the cell in response to gravity - when a plant tilts, the statoliths drop to the "new" bottom cell wall, causing AUXIN to redistribute to the new bottom of the root
27
Amyloplasts: ROOTS
a high concentration of auxin INHIBITS cell elongation, slowing growth on the lower side of the root, while cells develop normally on the upper side and cause the root to bend TOWARD the high concentration of auxin - causes the root to grow DOWN
28
Amyloplasts: SHOOTS
- opposite effect of auxin than in roots - a higher concentration stimulates cell expansion, causing the shoot to bend AWAY from the high concentration of auxin - after the root begins to grow vertically again, the Amyloplasts return to their normal position and auxin is equally distributed on both sides of the root tip
29
Growth Responses in Plants
- Apical Dominance - Leaf Abscission - Fruit Growth - Fruit Ripening
30
Apical Dominance
plant grows primarily at a single apical meristem and has limited lateral branches (would result in multiple meristems) - regulated by AUXIN at the apical meristem - auxin regulates cytokinin (which promote cell division, but only in the presence of auxin) - abscisic acid in the lateral buds inhibits the production of auxin, and removal of the apical bud will release this inhibition, allowing the lateral buds to grow
31
Leaf Abscission
Plants drop leaves in response to changing seasons (based on temperature, photo period, water, or other conditions); regulated by AUXIN + ETHYLENE interactions - during growth season, the leaf produces high levels of auxin, which blocks ethylene activity - as seasons change, auxin production lessens - lower auxin permits ethylene to initiate senescence, allowing the leaf to fall off in a controlled manner
32
Fruit Growth
promoted by GIBBERELLINS; artificial addition of GAs to fruit while still on plant causes them to grow larger than normal
33
Fruit Ripening
once grown to an appropriate size, fruits begin ripening, a process stimulated by ETHYLENE - form of senescence
34
Responses to Water/Water Stress in Plants
- Germination - Stomatal Closing - Local Cell Death
35
Water Response: Germination
The seeds of some plants rely on the intake of water to initiate germination rather than light - Water intake activates GA, which signals to transcribe AMYLASE, which breaks down the starch in the seed to initiate germination - when water is absent, germination is blocked by the hormone ABSCISIC ACID (ABA) - GA + ABA work in opposition in regulating germination responses
36
Stomatal Closing
activation of phot 1+2 by BLUE LIGHT cause the stomata to open to permit gas exchange so photosynthesis can occur - photosynthesis requires water - in a drought, ABA causes stomata to CLOSE, preventing gas exchange and halting photosynthesis - ABA response occurs even if blue light is present (signaling from drought via ABA OVERRIDES the signaling from blue light via phot1)
37
Abscisic Acid (ABA)
inhibits GA activity - used in response to water / water stress like drought
38
Local Cell Death
In droughts, the immediate response is stomatal closing. However, because closed stomata prevent gas exchange, the plant will die if they are closed for too long - if a drought persists, the plant will begin sacrificing areas by allowing leaves/stems to die in localized regions - produces ETHLYENE, which can induce localized cell death
39
Thigmotropism
movement in response to touch; SLOW and FAST thigmotropism
40
SLOW Thigmotropism
plant response to a touch stimulus that affects the direction of growth; regulated by AUXIN, which redistributes in the elongating stem in response to touch - results in differential stem elongation - EX: vines wrapping, growing along structures
41
FAST Thigmotropism
Rapid plant response to touch; occurs as a result of an electrical signal (like the animal nervous system) which causes rapid changes in cell turgor pressures and thus rapid movement of structures associated with those cells - EX: venus flytraps closing their mouth

BIOS TEST 3 (8 decks)

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