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Sem 1: Plant Biology > Week 7 > Flashcards

Week 7 Flashcards

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1
Q

What are examples of blue light responses in plants?

A

Chloroplast movements
Sun tracking by leaves
Phototropism
Photomorphogenesis - inhibition of hypocotyl elongation and stimulation of chlorophyll synthesis
Stomatal movements
Phototaxis
Anthocyanin accumulation
Regulation of gene regulation

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2
Q

What is the difference in function between phytochrome (red light) and blue light?

A

Red light –> presence and quality of light
Blue light –> presence and direction of light

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3
Q

What is phototropism?

A

The growth of plants through the influence of the direction of sunlight.
Positive means towards light
Negative means away from light

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4
Q

What are the stages for phototropism?

A

1- Light gradient
2- Unequal light perception
3- Unequal auxin concerntration
4- Unequal cell elongation (shaded side)
5- Bending

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5
Q

What mediates phototropism?

A

Auxins

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6
Q

What is the response of stem elongation in blue light?

A

In the blue light range a 3 finger (3 peaks) response occurs showing strong correlation with inhibition of stem elongation

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7
Q

When finding out the impact of blue light on inhibiting stem elongation how did they make sure Pr and Pfr didnt impact results?

A

Yellow light was used
Yellow light establishes constant Pr:Pfr ratio

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8
Q

What is the time that difference between phytochrome and blue light mediated stem elongation inhibition?

A

Red light: 8-90 minutes
Blue light: 15-30 seconds

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9
Q

What genes are impacted by blue light?

A

Chalcone synthase
RBCS
LHCB
SIG5

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10
Q

What is the general pattern for blue-light treatment in light responsive genes?

A

Takes time to respond when light is detected then increases as light increases before switching off when no blue light

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11
Q

What is the stomatal openening promoted by?

A

Photosynthesis (DCMU partially inhibits)
Blue light

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12
Q

What experimentally can inhibit stomatal opening?

A

Orthovanadate (inhibitor of H+-ATPase

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13
Q

What experimentally can induce stomatal opening?

A

Fusicoccin (activator of H+-ATPase)

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14
Q

What is the basic physiology of stomata opening in response to light?

A

1- Blue light
2- Uptake of ions and synthesis of organic solutes
3- Decreased water potential
4- Water influx
5- Swelling
6- Pore opening

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15
Q

What happens to ions in response to blue light?

A

Proton-ATPase = removes protons from cell
Ion channel = Input of K+ and Cl- due to ion differences

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16
Q

What is the K+ concerntration in a guard cell throughout the day?

A

Closed guard cell: 0.1 M
Open guard cell: 0.4-0.8M (peak)

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17
Q

What is the pattern for K+ concerntration throughout day?

A

Increases in response to blue light
Then peak mid morning
Decreases by late morning reaching lowest in the evening

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18
Q

With dropping K+ levels how is the water potential kept low?

A

With sucrose it is either transported in through sucrose transporters or manufactored in the cell from photosynthesis or starch

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19
Q

Other than sucrose what is another organic osmatically active compound that can also be made?

A

Malate^2- from phosphoenol pyruvate

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20
Q

What are the steps for transporting H+ across the cell membrane?

A

1- Serine/threonine protein kinase converts ATP to ADP + Pi
2- The Pi binds to the inactivated H+-ATPase then a 14-3-3 protein binds to the Pi activating the H+-ATPase
3- ATP is used to transport H+ across the membrane

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21
Q

What gene codes for cryptochromes?

A

CRY1 and CRY2

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22
Q

What happens to mutants in CRY?

A

Mutants lack blue light dependant inhibition of hopocotyl growth

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23
Q

How long is the CRY1 protein?

A

75 kDa

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24
Q

What are the two domains of the CRY1 protein?

A

PHR = Photolyase related domain
CCE= C-terminal Cryptochrome extension

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25
Q

What two molecules get added to the CRY1 protein?

A

Pterin and FAD both on the PHR section

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26
Q

What happens to anthocyanin accumulation in cry1 and cry1, cry2 plants?

A

Much less accumulation of anthocyanin compared to wildtype

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27
Q

What happens to hypocotyl length in cry1 and cry1, cry2 plants?

A

Much longer hypocotyls then in wildtype

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28
Q

In very low fluence light does cry1 and cry2 mutants impact phototropism?

A

Yes

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29
Q

What biological responses are mediated by crytochromes?

A

Photomorphogenesis
Flowering time and circadian rhythm
Anthocyanin accumulation
Phototropism (low fluence only: ‘first positive curvature)

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30
Q

What are the 2 mechanisms of CRYs?

A

1- Interacting with CIB transcription factors, which then interact with the FT gene to promote floral initiation
2- Interact SPA proteins to supress SPA activation of COP1-mediated degradation of HY5, HYH, CO and other regulators of light-regulated gene (LRG)

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31
Q

What is NPH1 protein?

A

Phototropin1 (PHOT1)

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32
Q

What are is the section on the end of the NPH1 protein?

A

Serine/theorine protein kinases

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33
Q

What are attachted to LOV1 and LOV2?

A

Co-enzymes FMN

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34
Q

What does NPH stand for?

A

Non-phototropic hypocotyl

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35
Q

What does LOV stand for?

A

Light, oxygen and voltage regulated

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36
Q

How does phot1 mutation impact phototropism?

A

Inhibits phototropism in moderate levels of blue light, responds to high levels of light

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37
Q

How does phot1 and phot2 mutation impact phototropism?

A

Inhibits phototropism in both medium and high levels of blue light

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38
Q

How does phot2 mutation impact chloroplast movement?

A

The chlorplasts in high levels of light are positioned as if they were in low levels of light so along the top and bottom not sides

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39
Q

How does phot1 and phot2 mutation impact chloroplast movement?

A

Little or no movement of chloroplasts

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40
Q

How does phot1, phot2 and phot1/phot2 mutation impact guard cell closer?

A

Both phot1 and phot2 impact guard cell opening
phot1/phot2 badly impact guard cell opening

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41
Q

What is zeaxanthin?

A

A carotenoids

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42
Q

What does zeaxanthin do?

A

Absorb blue light

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43
Q

How is zeaxanthin made during the xanthophyl cycle?

A

Violaxanthin is converted to zeaxanthin by the gene NPQ1 the reverse reaction is done by the gene DTT

44
Q

What does blue light do to zeaxanthin?

A

Serine/threonine protein kinase

45
Q

What does the activated serine/threonine protein kinase do?

A

Converts ATP to ADP + Pi. The Pi activates the proton ATP-ase pump when also binded with 14-3-3 protein allowing for protons to be pumped across

46
Q

What is photosynthesis?

A

The light dependant assmilation, fixation and reduction of CO2 into carbohydrates such as sucrose and starch

47
Q

What organisms can do photosynthesis?

A

Terrestrial and aquatic plants, algae and phytoplankton

48
Q

What is required for photosynthesis?

A

Light, water, carbon dioxide and mineral ions

49
Q

What is the name for an organism that can make its own food?

A

Autotrophs

50
Q

What wave length of solar radiation is used as an energy source for plants?

A

400-700nm, similar to the visible wavelengths of vertebrate eyes

51
Q

What is the formula to work out the formula for energy of a photon?

A

E=hv

52
Q

What does each letter stand for in the equation E=hv?

A

E = Energy of photon
h = Planck’s constant (J s^-1)
v = frequency

53
Q

How do you work out the frequency of a wave length?

A

c/λ

54
Q

What do the letters in v = c/λ mean?

A

v = frequency
c = velocity of light
λ = wavelength

55
Q

What does this mean for energy of blue light compared to red light?

A

Blue light has more energy than red light
Mole of photons of 400nm has 296 kJ of energy compared to 175kJ with a wavelength of 680nm

56
Q

What cellular machinary harvests the energy of light?

A

Complex assembly of proteins, pigments and cofactors located in the thylakoid membrane of chloroplasts

57
Q

What are the two assembelies associated with photosynthesis?

A

Photosystem 1
Photosystem 2

58
Q

What are the pigments associated with the photosystems?

A

Multiple carotenoids, chlorophyll a, chlorophyll b and a single chlorophyll a molecule in complex with protein in the reaction centre

59
Q

What wave lengths do the two chlotophyll pigments absorb?

A

680nm (Pigment 680 or P680)
700nm (Pigment 700 or P700)

60
Q

How else can photosystems recieve energy?

A

The non-radiative process of fluorescence resonance energy transfer (FRET) from neighbouring chlorophyll molecules

61
Q

How does chlorophyll capture light?

A

Light promotes (excites) electrons into higher energy states, from which energy may be lost as heat or fluorescence or transferred by FRET

62
Q

What happens to an excited electron on the chlorphyll with a reaction centre?

A

The excited electron maybe lost, transferred via another chlrophyll to the electron acceptor phaeophytin

63
Q

What happens to the chlorophyll with a reaction centre, now it has lost an electron?

A

The chlorophyll now has a postitive charge and is very reactive

64
Q

How does the positvely charged chlorophyll with a reaction centre regain its lost electron?

A

An electron is abstracted from water by oxygen evolving complex (OEC) and then given to the reaction centre chlorophyll

65
Q

What happens to the water after the electron is abstracted?

A

It splits to form O2 and H+, these then are released on the lumen side of the membrane

66
Q

How does the exciting of an electron impact phaeophytin?

A

It impacts the conversion of light energy into redox energy. The more negative the redox potential the greater the potential to do work

67
Q

What happens to the original excited electrons?

A

They are passed successively down a redox chain of lipid (plastoquinone) and protein carriers to the chlorophyll (P700) reaction centre of PS1

68
Q

What happens to the redox energy of the electrons as they are passed down?

A

They lose redox potential energy which is converted into a proton gradient (proton motive force, pmf)

69
Q

How can the pmf be dissipated?

A

Through the movement of protons through a protein complex called ATP synthase, from the lumen back into the stroma, which is coupled with ATP synthesis
pmf is converted into chemical energy

70
Q

What happens to the electron after photosystem 2?

A

It gets passed to the reaction centre P700 chlorophyll of PS1 fills the electron ‘hole’ created in the P700 chlrophyll on excitation of it by light or FRET from neighbouring chlorophyll molecules.

71
Q

What happens to the P700 chlorophyll now it has an excited electron?

A

The chlorophyll has a high -ve redox potential, it donates the electron to series of protein carriers, these are oxidised are they pass it on, before getting to the molecule NADP+ on the stromal side generating NADPH

72
Q

What is a key characteristic of NADPH?

A

It is a strong reducing agent

73
Q

What are the 2 principle products of the light dependant reactions?

A

ATP and NADPH which are the energy and reducing currency of the fixation of carbon dioxide

74
Q

What is the benson-calvin cycle?

A

The reductive pentose pathway, which accounts for practically all of the reduced cabon in the bioshpere

75
Q

What organisms do the benson-calvin cycle?

A

It occurs in algae and higher plants, even in organisms whichhave additonal mechanisms it stll ‘refixes’ CO2 released by the additional processes

76
Q

Where does the benson-calvin cycle occur?

A

In the chloroplasts

77
Q

What does the benson-calvin cycle comprise of?

A

A cycle of biochemical reactions, a series of pools of metabolites, connected by enzymes, from which a proportion of reduced carbon (triose phosphate, a 3 carbon sugar) is withdrawn for biosynthetic processes.

78
Q

What biochemical reactions occur in the benson-calvin cycle?

A

Sucrose synthesis for export to distal parts of higher plants
Starch synthesis locally in chloroplasts
Starch synthesis in distal sink organs e.g developing tubers

79
Q

What is the chemical processes that occur in the overall cycle Light independant photosynthesis?

A

A reductive process, which replaces some of the valencies of carbon atoms occupied by oxygen (in CO2) with hydrogen atoms (sugars eg glucose)

80
Q

What is the first stage of the benson-calvin cycle?

A

Carboxylation of ribulose bisphosphate to yield an unstable 6 carbon intermidiate which breaks down to form 2 molecules of 3-phosphoglyceric acid. This is catalysed by ribulose biphosphate carboxylase/oxygenase (most abundant enzyme on earth)

81
Q

What is the second stage of the benson-calvin cycle?

A

Reduction of 3-phosphoglyceric acid to triose phosphate in a two step process

82
Q

What are the products used to convert 3-phosphoglyceric acid to triose phosphate?

A

The products of the light reaction, ATP and NADPH

83
Q

What happens to the triose phosphate?

A

Either:
Exported from the chloroplast into the cytosol for sucrose synthesis
Used in starch synthesis in the chloroplast

84
Q

What is the third phase of the benson-calvin cycle?

A

The complicated rearrangement of five molecules of 3C triose phosphate to yield 3 molecules of 5C ribulose phosphate. A final reaction consumes one ATP molecules per ribulose phosphate molecule to give the ribulose biphosphate ‘starting material’

85
Q

What is the conversion rate of CO2 in the benson-calvin cycle?

A

The addition of one CO2 at each turn of the cycle has the consequence that for every three turns, one molecule of triose phosphate is assimilated. Though turns are concurrent with metabolite pools are accessed by multiple copies of enzymes at a time

86
Q

What is the time lag between carbon assmilation and lights being turned off?

A

A significant delay of 30 seconds

87
Q

Why is there a delay in carbon assimilation and the lights being turned off?

A

The photochemical events stop instantly but the electron transfer steps are complete in msecs. The measured assimilation of CO2 processeds for 30 seconds depleting the chloroplast pools of ATP and NADPH

88
Q

What maintains the CO2 concerntration gradient?

A

The consumption, fixation into water-soluble triose phosphate

89
Q

What happens to the CO2 when it enters the leaf to its carboxylation by Rubisco?

A

CO2 must diffuse through the stomata into the leaf air space
CO2 then dissolves into the aqueous milieu of the cell walls of the mesophyll cells
CO2 diffuses across the plasma membrane into the cytosol and across the membrane of the chloroplast into the stroma

90
Q

Which stage of the movement of CO2 into the leaf and to the Rubisco has the most diffusive resistance?

A

The diffusion into the stoma

91
Q

What is the solubility of CO2 in water at equilibrium with atmospheric CO2 at 10°C?

A

17µM which is similar to the Km of the enzyme, this is half of the maximal rate

92
Q

What is the solubility of O2 in water at equilibrium with atmospheric O2 at 10°C?

A

350µM

93
Q

What impact does oxygen have on CO2 fixation by Rubisco?

A

Rubisco has a competing oxygenation reaction with O2, meaning CO2 fixation is limited as oxygen concerntration inceases and vica versa

94
Q

What is the concentration of CO2 in the air space of an actively fixing Rubisco?

A

200 ppm (µL -1)

95
Q

What is the concentration of CO2 in the air?

A

370ppm

96
Q

What is the concentration of water in the air at 100% humidity?

A

1.3mM

97
Q

What is the concentration of water in the air at 70% humidity?

A

0.91mM

98
Q

What the difference between the gradient of water and CO2 from atmosphere to plants?

A

The gradient is much larger for water than it is for CO2, meaning plant loses more water than it assmiilates CO2 on a mole per mole basis

99
Q

What is the water use effciency for CO2 assmilated in both C3 and C4 plants?

A

C3- 1-3g CO2 fixed/ kg water transpired
C4- 2-5g CO2 fixed/ kg water transpired

100
Q

What is the CO2 concentration in greenhouses?

A

1000 ppm for yield increase

101
Q

What happens to CO2 yields in labs when O2 levels are decreased?

A

Increased yelds of photosynthetic CO2 fixation in C3 plants

102
Q

What is a potential reason for why O2 substrate is used in higher concerntrations?

A

The O2 substrate leads through a complicated biochemical pathway which leads to the release of CO2. This is photorespiration

103
Q

What is the overall chemical consumption and liberation of photorespiration?

A

Photorespiration consumes O2 and ATP (light reaction product), liberating CO2. This works in opposition to photosynthesis and works with respiration liberating CO2

104
Q

What is the ratio of O2 used and CO2 lost?

A

2 O2 to 1 CO2

105
Q

What happens during photorespiration?

A

Rubisco generates phosphoglycerate (3C) which is recycled in the Calvin cycle and a 2C molecule that i shunted off to other organelles. Two 2C molecules combine, one CO2 is lost and the remaining 3C compound finds its way back to the Calvin cycle

106
Q

How significant are the CO2 loss by photorespiration?

A

In C3 species, up to 40% of CO2 fixed may be lost through this route, usually 20%

107
Q

What conditions is CO2 lost by photorespiration?

A

High light, high temperature environements or where CO2 concentrations are low eg aquatic envrironments, where incidentally the diffusive resiatnce is much higher

Sem 1: Plant Biology (10 decks)

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