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Sem 1: Plant Biology > Week 4 > Flashcards

Week 4 Flashcards

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1
Q

How abundant is sulfur?

A

Sulfur is the 5th most abundant by mass on earth

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2
Q

What are the problems caused by atmospheric sulphur emission?

A

Sulphur Dioxide leads to acid rain and can cause extensive damage to vulnerable plants

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3
Q

What are the problems with removing sulphur from the atmosphere?

A

Eliminating sulphur from air pollution uncovered crop plant deficincies, particularly in oilseed rape and wheat

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4
Q

Which inorganic forms of sulphur have a -2 oxidation state?

A

Sulfides
S^2-, H2S, R-SH

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5
Q

Which inorganic forms of sulphur have a 0 charge?

A

Sulphurs
S^0, S8

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6
Q

Which inorganic form of sulphur have a +4 charge

A

Sulphur Dioxide
S02
Sulfites
SO3-

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7
Q

What inorganic form of sulphur have a +6 charge?

A

Sulphate
SO4^2-

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8
Q

Which forms of sulphur do plants uptake?

A

Primarily SO4^2- but to a lesser extent SO2 or H2S

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9
Q

Where does atmospheric sulphur come from?

A

Volcanic activity
Combustion of fossil fuels
Salt marshes
Ocean

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10
Q

What form is the atmospheric sulphur?

A

Mostly SO2 but also other chemicals like dimethl sulphide (DMS)

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11
Q

What is the main series of chemical reactions that take place with sulphur in the atmosphere?

A

H2S –> SO2 –> SO4^2-

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12
Q

Which form causes acid rain?

A

SO4^2 (sulphuric acid)

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13
Q

What happens to SO2 and H2S?

A

Assimilation by plants

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14
Q

What happens to the sulphur after the plant dies or is eaten?

A

The sulphur is released as R-SH through decomposition or in manure

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15
Q

What is the process in which R-SH is converted to SO4^2-?

A

Prokaryotic oxidation

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16
Q

What is the formulas for the conversion between R-SH to SO4^2-?

A

R-SH –> S –> SO4^2-

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17
Q

Can SO4^2- be converted to R-SH?

A

Yes, through the process of Prokaryotic reduction

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18
Q

How have SO2 emissions and SO4^2- precipitation changed?

A

They have been on a decline since the 1980s

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19
Q

Which amino acids contain sulphur?

A

Cysteine
Methionine

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20
Q

Which chemicals containing in sulphur are useful for plant defences?

A

Camalexin - induced by pathogens
Glucosinolates - anti-herbivores

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21
Q

What is the function of the compound glutathione?

A

Glutathione is an amino acid derivative involved in reactions

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22
Q

Which sulphur containing molecules that provide a flavor or odor?

A

Mercapto-p-menthan-3-one (blackcurrant)
Allicin (garlic flavour)
Allyl-isothiocyanate (horseradish flavour)

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23
Q

What uptakes sulfate?

A

Sulfate uptake occurs primarily through SULTR transporters

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24
Q

How many SULTR transporters do Arabidopsis have?

A

12 genes that code from SULTR that fall into 4 groups

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25
Q

Which 2 SULTR genes do most primary assimilation occurs?

A

Through SULTR 1;1 and SULTR 1;2 genes

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26
Q

What happens at a SULTR transporter?

A

A co-transporters between H+ and SO4^2-

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27
Q

What is the function of group 1 transporters in Arabidopsis?

A

High affinity sulphate transporters (root/shoot)

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28
Q

What is the function of group 2 transporters in Arabidopsis?

A

Low affinity sulphate transporters (root/shoot)

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29
Q

What is the function of group 3 transporters in Arabidopsis?

A

Root,shoot,very low affinity alone, but enhance affinity of Group 2
Also intracellular, sulfate into chloroplasts

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30
Q

What is the function of group 4 transporters in Arabidopsis?

A

Intracellular, sulfate to and from vacuoles

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31
Q

What SULTR group transports SO4^2- out of the vacuole?

A

Group 4

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32
Q

What is the SO4^2- concerntration in the vacuole, cytosol and chlorphyll?

A

6-75 mM vacuole
1-11 mM Cytosol
4-12 mM Chlorophyll

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33
Q

What are the key feature of SULTRs?

A

They are non-overlapping

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34
Q

Which SULTR group transports chemicals into the chloroplasts?

A

Group 3

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35
Q

Where do sulfate reduction occurs?

A

Only in plastids

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36
Q

What is the function of the S transporters?

A

They coordinate long distance transporters

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37
Q

What are the major sinks of sulphur?

A

Shoot apex - meristem, elongation zone, cell differentiation
Developing leaves
Roots tips - elongation zone, meristem
Generative organs (seeds)

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38
Q

What are the major sources of sulphur in plants?

A

Mature leaves
Mature roots

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39
Q

What happens to sulphur when it enters the plant?

A

Enters through leaf and gets distrubuted through the phloem to the parts of the leaf that require large amounts of sulphur where it is downloaded

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40
Q

What is the process converting sulphate converted into cysteine?

A

Sulphate –> APS (Adenosine 5’-phosphosulphate) –> Sulphite –> Sulphide –> Cysteine

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41
Q

What is an alternative pathway for APS?

A

APS –> PAPS (5’-Phosphoadenosine 3’-phosphosulphate) –> Then to sulfated compounds

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42
Q

What is an alternative product for sulphite?

A

Sulfoquinosovyl diacylglycerides

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43
Q

What is the pathway between the conversion between serine and cysteine?

A

Serine –> O-acetylserine –> cysteine

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44
Q

What is the pathway between cysteine and methionine?

A

Cycteine –> Cystathionine –> Methionine (reversable reaction) –> S-adenosyl methionine

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45
Q

What is the reaction to form Adenosine 5’-phosphate (APS)?

A

Sulphate + ATP using the enzyme ATP sulfurylase

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46
Q

What happens during the converison of APS to sulphite?

A

Using APS reductase APS is conveted to sulphite this releases AMP and converts 2 Glutathione (GSH) to Glutathione disulfide (GSSG)

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47
Q

What happens to the conversion between Sulphite and Sulphide?

A

Using Sulphite reductase FdxRed is oxidised to form FdxOx

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48
Q

Where does APS to Sulphite and Sulphite to Sulphide occur?

A

Exclusively in plastids

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49
Q

How is the alternate pathway between APS and PAPS?

A

Using ATP and the enzyme APS kinase forming PAPS and ADP

50
Q

How is sulphide assimilated into cycteine?

A

Using O-Acetylserine (thiol)lyase (OAS-TL) swapping the COCH3 with SH

51
Q

How is serine converted into O-acetylserine?

A

Serine is bonded with acetyl-CoA using Serine Acetyltransferase

52
Q

What is useful to identify an issue if there is a large concerntration of OAS?

A

It builds up when sulphur is low

53
Q

What enzymes make up the cysteine sythnase complex?

A

Serine Acetyltransferase (SAT)
O-Acetylserine (thiol)lyase (OAS-TL)

54
Q

Where is cysteine synthase complex?

A

Found in the cytosol, plastid and mitochondria

55
Q

What happens to OAS when SO4^2- is unavaliable?

A

When SO4^2- is unabaliable OAS accumulates causing the CS complex to dissociate and decreasing the activity of SAT. Therefore OAS production decreases

56
Q

What does SLIM do?

A

SLIM (EIL3) (master gene) coordinates many transcriptional responses to S.

57
Q

What does Thioglucosidase do?

A

Thioglucosidase activity (increased by S-deficiency) liberates S for recycling for example in glucosinolates

58
Q

What regulates sulphur uptake and assimilation rates?

A

Local sulfate levels
OAS
Reduced sulphur (glutathione, Cys etc)
Light, carbon, nitrogen reserves, cicadian rhythms etc

59
Q

What regulates SULTR genes?

A

Transcriptional, post-transcriptional and post translational/ allosyeric regulation of transporters

60
Q

What regulates ATP sulfurylase and APS reductase?

A

Transciptional regulation of ATP sulfurylase and APS

61
Q

What regulates Cys synthase?

A

Allosteric interactions and metabolic regulation

62
Q

When Sulphur is low what happens to SULTR?

A

They are up regulated to assimilate more sulphur

63
Q

What genes are down regulated in low sulphur levels?

A

Some of them are:
MAM1
MAML
BCAT

64
Q

What is the name of the toxic sulphur defence found in Brassicas?

A

The ‘mustard oil bomb’ contains glucosinolate break down products

65
Q

How is the ‘mustard oil bomb’ produced?

A

S cells produced and store glucosinolates. When they are acted upon by myrosinase they form secondary producted that act as a ‘mustard bomb’ eg isothiocyanate is found in horse raddish

66
Q

What is the consequence of stricter sulphur laws?

A

Less sulphur enters soils and plants are more prone to sulphur deficiency which can be augemented with sulphur fertilizers like elemental sulphur

67
Q

What are key facts about Phosphorus?

A

The 11th most abundant element
5th most abundant element in a plant
1st or 2nd most limiting nutrient

68
Q

What is the role of Phosphorus for plants?

A

Roles in cell structure, energy and information storage and energy and information transfer

69
Q

What are the biomolecules that phosphorus found in?

A

DNA, RNA, Membrane phospholipids, Bones/Teeth and phosphorylation (signalling)

70
Q

What form is phosphorus assimilated as?

A

Phosphate which depending on the pH is H2PO4^-, HPO4^2- and PO4^3-

71
Q

What is the phosphorus cycle (preindustrial)?

A

Slow weathering of rocks
Terrestial cycle (assimialtion, then eaten finally ending up as manure or decomposing)
Slow leaching to lakes and oceans
Sedimentation
Upwelling

72
Q

What are the impacts on the phosphorus cycle since global industrialisation?

A

Mining and commercial processing accelerates P entry to bioshpere
Sewage and modern practices accelerate runoff
Urbanisation removes P from terrstrial cycle and accelerates entry to waterways, causing toxic algal blooms (eutrophification)

73
Q

What is accumulation factor?

A

The degree of enrichment required in plant cells compared to the environment

74
Q

What is the accumulation factor for the macronutrients?

A

P - 6000
N - 50
K - 30
S - 10
Ca - 5
Mg - 5

75
Q

Why is phosphorus insoluble when in soil?

A

They are in isoluble complexes as in cation-phosphate complexes. These are relatively insoluble and immoble. These include oxides and hydroxides of Al and Fe
Plants dont take up in organic phosphate

76
Q

What is Labile P?

A

Amount or proportion of any P that is readily liberated from a phosphate-containing compound by hydrolysis

77
Q

How much more phosphate is moved now than natural (pre-agricultural era)?

A

4 times

78
Q

What happens to phosphate avaliablity when pH changes?

A

5.5 to 7 pH optimum
Below 5.5: Fixation by Fe, Al, Mn
Above 7: Fixation as calcium phosphates

79
Q

What happens to phosphate used in agriculture?

A

Phosphates react with Al, Fe, K and Mg
Compounds are relatively insoluble/ immobile (P fixation)
Traditional belief was that fixation is rapid, dormant and irreversible
Crops actually acquire 50-70% of applied P fertilizer

80
Q

What was the consequence of not understanding P fixation?

A

Overuse of fertilizer (N:P of 1.5:1)

81
Q

What is the ratio of N:P now in agriculture?

A

N:P
6:1

82
Q

What is eutrophication?

A

Increased biomass production (algal blooms)
Decrease O2 concerntrations
Ecosystem collapse

83
Q

What happens to chlorophyll when there is low P?

A

Decreased production of cholrophyll leading to decrease in dry mass

84
Q

Where does nutrient uptake take place?

A

Uptake across the plasma membranes of root cortex or endodermal cells

85
Q

What can plasma membranes do to help the plant uptake the right nutrient?

A

Selectivity of which nutrients are absorbed by the cortex and endodrmis

86
Q

How many families of plant phosphate transporters are there?

A

3

87
Q

What is the function of plant phosphate transporter 1?

A

Pht1 localised in the plasma membranes
H+/PO4^3- co transporters that acquire Pi from the rhizosphere
12 membrane-spanning domains

88
Q

Where is PHt 2 located?

A

Chloroplast

89
Q

Where is PHt located?

A

Mitochondria

90
Q

What is the function of PHt?

A

Uptake P at root/soil interface and translocation within the plant

91
Q

Where are most PHt 1 expressed?

A

Root tissues

92
Q

How many PHt1 genes do Arabidopsis have?

A

9

93
Q

How many PHt1 genes do rice have?

A

13

94
Q

How many PHt1 genes do poplar have?

A

12

95
Q

What is the relationship between mycorrhiza and PHt 1?

A

Some PHt 1 are mycorrhiza inducible

96
Q

What is Rhizosphere?

A

Microzone that is around plant roots and is influenced by chemicals released by plant

97
Q

What chemicals impact the Rhizosphere?

A

Sugars
Mucilage
Phenolics
Organic acids
Phosphatases

98
Q

How do many species respond to to nutrient defiencies?

A

They release H+ and organic acids

99
Q

Why do plants released acids and protons into the soil?

A

Low pH helps to solubilise these nutrients, which otherwise would be bound to soil particles and be unavaliable

100
Q

What are carboxylates?

A

Citrate, malate and malonate

101
Q

Why are carboxylates released into the soil?

A

The carboxylates released into soil form complexes to the metal cations bound to phosphate. This releases phosphate by ligand exchange

102
Q

Why are protons also released along with carboxylates?

A

To balance the ionic charge

103
Q

How much of soil Pi is bound to organic P?

A

30-80%

104
Q

What root traits are associated with enhanced phosphate uptake?

A

Reduced gravitropism
Increased formation and elongation of lateral roots and root hairs
Aerenchyma (air spaces that allow metabolically inexpensive growth), particularly in aquatic plants)

105
Q

What does low P promote in roots?

A

Low P promotes shallower roots, enabiling the plant to exploit the higher P concerntrations near the soil surface

106
Q

What is the advantage of root ‘foraging’?

A

Enables plants to rapidly colonise nutrient-rich pathches of soil
Important when xploiting immobile nutrients
Also beneficial for NO3^-, when plants are in competition

107
Q

What are root hairs?

A

Small hair like extensions of the epidermis of the root in which water-filled soil pores that would be inaccessible to roots

108
Q

Which cells do root hairs extend out of?

A

Specilised trichoblast cells

109
Q

What do root hair cells do?

A

Increase surface area
Increase nutrient depletion zone

110
Q

How does P deficiency impact root hairs?

A

Increases root hair lengths and density

111
Q

What are the advantages of tapping into the mycorrhizal fungi?

A

Increase effective reach of their roots

112
Q

How many plants have a symbiotic relationship with mycorrhizal fungi?

A

80% (roughly)

113
Q

How long ago did the plant mycorrhizal fungi relationship form?

A

450+ mya

114
Q

Why is it believed that this relationship formed?

A

Surrogate roots for first land plants

115
Q

What is the main role of the symbiotic relationship?

A

Thought to be phosphate uptake

116
Q

Which plants can’t form this symbiotic relationship?

A

Arabidopsis and other Brassicaceae

117
Q

What forms in plant cells as a result of the arbuscular mycorrhizal fungi relationship?

A

Fungal arbuscules

118
Q

What is the internal structure when this relationship happens?

A

Peri-abscular membrane and peri-arbuscular space form to allow diffusion and to prevent plant from attacking fungi.
This forms next to the arbuscule cell wall and membrane

119
Q

What form is the Pi translocated?

A

As a polyphosphate

120
Q

Which symbiotic relationships can legumes form?

A

With both rhizobia and AM fungi

121
Q

How does the AM fungi, plant symbiotic relationship form?

A

Fungi releases Myc factor, triggering strigolactones to be released by plant
A Fungal hyphopodium forms along with the plant forming pre-penetration appratus
This allows the fungus to enter the plant allowing for the arbuscle to form

Sem 1: Plant Biology (10 decks)

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