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Biology of Plants: Exam 1 > Lecture 2: Seed Germination, dormancy, and the environment > Flashcards

Lecture 2: Seed Germination, dormancy, and the environment Flashcards

1
Q

Plant Developmental Stages

A
  1. Seed
  2. Seedling (stage when cotyledons still attached)
  3. Vegetative (juvenile)
  4. Adult reproductive
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2
Q

Germination

A

The transition between seed and seedling

- see seed coat rupture and embryonic root start to come up

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3
Q

Factors affecting germination

A

Many factors, relative importance varies by species

  • physical attributes
  • chemical signals including plant hormones
  • light
  • temperature
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4
Q

Dormancy

A
  • State of seed in which germination does not occur although conditions are generally favorable
  • influences composition of seed bank
  • preventing germination
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5
Q

Enforced dormancy (quiescent seeds)

A

Germination occurs easily when conditions are right

- example: seeds you buy at the store - you don’t have to break dormancy

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6
Q

Primary or innate dormancy

A

Seeds dormant on release from mother plant

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7
Q

Secondary or induced dormancy

A

Occurs if conditions are unfavorable for germination

- then must break the dormancy

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8
Q

Seed bank

A

Seeds being stored underground in the soil

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9
Q

Imbibition

A
  • when the seed takes in water, which triggers the cellular growth and replication that allows the seed to germinate
  • specifically with seeds
  • absorption of H2O
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10
Q

Scarification

A
  • rubbing seeds between sandpaper or soaking them in acid

- Mechanical (sanding) and chemical treatments (sulfuric acid)

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11
Q

Strophiole

A

Preformed weak site where imbibition begins

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12
Q

Testa

A
  • Hard seed coats

- thickness varies among species

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13
Q

Chemical factors

A
  • water soluble germination inhibitors in pericarp or testa
  • nitrate (NO3-)
  • smoke
  • plant hormones - ABA & GA
  • moderate rains wash away specific organic compound or accumulated salts
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14
Q

Nitrates

A
  • many ruderal species stimulated by nitrate
  • gap-detection mechanism
  • large plant biomass depletes soil of nitrate
  • in the absence of vegetation mineralization & nitrification causes nitrate to accumulate breaking dormancy
  • required for plant growth and survival
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15
Q

Gap-detection mechanism

A

Suggests the available nitrate to take up, and if there are fewer plants in an area then it is ok to germinate
- I.e. Gap in understory, a break in the plant coverage so it is place to germinate

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16
Q

Ruderal species

A

Weedy species

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17
Q

Abscisic Acid (ABA)

A

high levels tend to prevent germination

- Phytohormone

18
Q

Gibberellic Acid

A

high levels tend to release dormancy by loosening cell walls and converting starch to sugar

  • seed can then take advantage of sugar
  • phytohormone
  • Gibberellins are applied to large amount of barley seeds to induce germination at the same time
  • Germinated seeds are then blasted with high heat to halt germination and caramelize sugars to create malted barley
19
Q

Stratification

A

breaking seed dormancy through exposure to low temperatures

  • aka long exposure to cold temperatures
  • mimicked by people placing seeds between moist layers of sand or paper towels in a refridgerator
20
Q

Temperature

A
  • temp fluctuations felt more acutely near top of soil

- temp fluctuations dampened at deep soil depth or water depth, and under neighbors

21
Q

Temperate Climate

A

summer annuals set seed in fall and germinate in spring

  • **Require long exposure to low temps
  • i.e. Hairy bittercress, Cardamine hirsuta
22
Q

Mediterranean Climates

A

Winter annuals set seed in late spring and germinate in fall

  • **Require long exposure to high temps
  • i.e. Dwarf plantain, Plantago virginica
23
Q

pigment Phytochrome

A
  • a small protein with light detecting portion, the chromophore
  • detects presence or absence of red and far-red light
  • absorbs light thereby changing protein folding that begins a series of signal transductions which end in a response
  • if seeds are close to soil surface or not shaded by neighbors, the Red-Far red light ration increases and vice versa
24
Q

Chromophore

A
  • the light detecting portion of the pigment Phytochrome
25
Q

Pr

Phytochrome red

A
  • red light absorbing form

- is the cis form isomer

26
Q

Pfr

Phytochrome far-red

A
  • far-red light absorbing form

- is the trans form isomer

27
Q

Cuticle

A

helps control seed moisture; waxy

28
Q

subcuticular layer

A

protection

29
Q

lumen of Malphghian cell

A
  • palisade cell layer - long, cylindrical cells
30
Q

Ostesclerid cells

A

tough, protect seed

31
Q

Structure of the Pr and Pfr

A
  • the chromophore undergoes a cis-trans isomerization at carbon 15 in response to red and far-red light
  • structure of the Pr and Pfr forms of the chromophore and the peptide region bound to the chromophore
32
Q

A light requirement:

A
  • prevents fatal germination of seeds buried too deep
  • indicates absence of established vegetation or a soil disturbance - gap detection (detects the presence and location of neighbors)
  • indicates status of leaf canopy by effects on spectral composition. Light under leaf canopy has low R:FR, which can prevent seed germination
33
Q

the Pr form

A
  • absorbs at a peak of 666 nm
  • is the form synthesized in dar-grown seedlings
  • when Pr absorbs red light, it is converted to the Pfr form
34
Q

the Pfr form

A
  • absorbs at a peak of 730 nm
  • the Pfr form is the active form that initiates biological responses
  • when Pfr absorbs far red light, it is converted to the Pr form
  • Pfr can also spontaneously revert to the Pr form in the dark over time = dark reversion
35
Q

Phytochrome example

A
  • lettuce seeds grown in the dark do no receive enough red light to switch the phytochrome to an active state and germination does not occur (a photomorphogenic response)
  • will germinate if exposed to 1 min. of red light
  • but, if red light treatment followed by few minutes of far-red light then no germination
36
Q

What is fluence?

A
  • fluence = amount of light over a given area
  • i.e. micromoles of quanta per meter squared
  • fluence rate, (Irradiance/light intensity)
37
Q

Very low fluence response

A
  • VLFR: reciprocity (reverts) not FR (far-red) reversible -> stays in Pfr form
  • tiny bit of red light
38
Q

Low fluence response

A
  • LFR: reciprocity FR reversible -> far-red reversible
39
Q

High-irradiance response

A
  • HIR: needs long exposure, no reciprocity

- not FR reversible

40
Q

Law of Reciprocity

A
  • magnitude of response dependent on the product of the fluence rate and the time of irradiation
  • has the amount been met and has it been for a certain amount of time
41
Q

Photon Flux Density

A
  • how many packages of light are illuminating a given area over a given time

Biology of Plants: Exam 1 (5 decks)

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