Week 4 Flashcards
How abundant is sulfur?
Sulfur is the 5th most abundant by mass on earth
What are the problems caused by atmospheric sulphur emission?
Sulphur Dioxide leads to acid rain and can cause extensive damage to vulnerable plants
What are the problems with removing sulphur from the atmosphere?
Eliminating sulphur from air pollution uncovered crop plant deficincies, particularly in oilseed rape and wheat
Which inorganic forms of sulphur have a -2 oxidation state?
Sulfides
S^2-, H2S, R-SH
Which inorganic forms of sulphur have a 0 charge?
Sulphurs
S^0, S8
Which inorganic form of sulphur have a +4 charge
Sulphur Dioxide
S02
Sulfites
SO3-
What inorganic form of sulphur have a +6 charge?
Sulphate
SO4^2-
Which forms of sulphur do plants uptake?
Primarily SO4^2- but to a lesser extent SO2 or H2S
Where does atmospheric sulphur come from?
Volcanic activity
Combustion of fossil fuels
Salt marshes
Ocean
What form is the atmospheric sulphur?
Mostly SO2 but also other chemicals like dimethl sulphide (DMS)
What is the main series of chemical reactions that take place with sulphur in the atmosphere?
H2S –> SO2 –> SO4^2-
Which form causes acid rain?
SO4^2 (sulphuric acid)
What happens to SO2 and H2S?
Assimilation by plants
What happens to the sulphur after the plant dies or is eaten?
The sulphur is released as R-SH through decomposition or in manure
What is the process in which R-SH is converted to SO4^2-?
Prokaryotic oxidation
What is the formulas for the conversion between R-SH to SO4^2-?
R-SH –> S –> SO4^2-
Can SO4^2- be converted to R-SH?
Yes, through the process of Prokaryotic reduction
How have SO2 emissions and SO4^2- precipitation changed?
They have been on a decline since the 1980s
Which amino acids contain sulphur?
Cysteine
Methionine
Which chemicals containing in sulphur are useful for plant defences?
Camalexin - induced by pathogens
Glucosinolates - anti-herbivores
What is the function of the compound glutathione?
Glutathione is an amino acid derivative involved in reactions
Which sulphur containing molecules that provide a flavor or odor?
Mercapto-p-menthan-3-one (blackcurrant)
Allicin (garlic flavour)
Allyl-isothiocyanate (horseradish flavour)
What uptakes sulfate?
Sulfate uptake occurs primarily through SULTR transporters
How many SULTR transporters do Arabidopsis have?
12 genes that code from SULTR that fall into 4 groups
Which 2 SULTR genes do most primary assimilation occurs?
Through SULTR 1;1 and SULTR 1;2 genes
What happens at a SULTR transporter?
A co-transporters between H+ and SO4^2-
What is the function of group 1 transporters in Arabidopsis?
High affinity sulphate transporters (root/shoot)
What is the function of group 2 transporters in Arabidopsis?
Low affinity sulphate transporters (root/shoot)
What is the function of group 3 transporters in Arabidopsis?
Root,shoot,very low affinity alone, but enhance affinity of Group 2
Also intracellular, sulfate into chloroplasts
What is the function of group 4 transporters in Arabidopsis?
Intracellular, sulfate to and from vacuoles
What SULTR group transports SO4^2- out of the vacuole?
Group 4
What is the SO4^2- concerntration in the vacuole, cytosol and chlorphyll?
6-75 mM vacuole
1-11 mM Cytosol
4-12 mM Chlorophyll
What are the key feature of SULTRs?
They are non-overlapping
Which SULTR group transports chemicals into the chloroplasts?
Group 3
Where do sulfate reduction occurs?
Only in plastids
What is the function of the S transporters?
They coordinate long distance transporters
What are the major sinks of sulphur?
Shoot apex - meristem, elongation zone, cell differentiation
Developing leaves
Roots tips - elongation zone, meristem
Generative organs (seeds)
What are the major sources of sulphur in plants?
Mature leaves
Mature roots
What happens to sulphur when it enters the plant?
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
What is the process converting sulphate converted into cysteine?
Sulphate –> APS (Adenosine 5’-phosphosulphate) –> Sulphite –> Sulphide –> Cysteine
What is an alternative pathway for APS?
APS –> PAPS (5’-Phosphoadenosine 3’-phosphosulphate) –> Then to sulfated compounds
What is an alternative product for sulphite?
Sulfoquinosovyl diacylglycerides
What is the pathway between the conversion between serine and cysteine?
Serine –> O-acetylserine –> cysteine
What is the pathway between cysteine and methionine?
Cycteine –> Cystathionine –> Methionine (reversable reaction) –> S-adenosyl methionine
What is the reaction to form Adenosine 5’-phosphate (APS)?
Sulphate + ATP using the enzyme ATP sulfurylase
What happens during the converison of APS to sulphite?
Using APS reductase APS is conveted to sulphite this releases AMP and converts 2 Glutathione (GSH) to Glutathione disulfide (GSSG)
What happens to the conversion between Sulphite and Sulphide?
Using Sulphite reductase FdxRed is oxidised to form FdxOx
Where does APS to Sulphite and Sulphite to Sulphide occur?
Exclusively in plastids
How is the alternate pathway between APS and PAPS?
Using ATP and the enzyme APS kinase forming PAPS and ADP
How is sulphide assimilated into cycteine?
Using O-Acetylserine (thiol)lyase (OAS-TL) swapping the COCH3 with SH
How is serine converted into O-acetylserine?
Serine is bonded with acetyl-CoA using Serine Acetyltransferase
What is useful to identify an issue if there is a large concerntration of OAS?
It builds up when sulphur is low
What enzymes make up the cysteine sythnase complex?
Serine Acetyltransferase (SAT)
O-Acetylserine (thiol)lyase (OAS-TL)
Where is cysteine synthase complex?
Found in the cytosol, plastid and mitochondria
What happens to OAS when SO4^2- is unavaliable?
When SO4^2- is unabaliable OAS accumulates causing the CS complex to dissociate and decreasing the activity of SAT. Therefore OAS production decreases
What does SLIM do?
SLIM (EIL3) (master gene) coordinates many transcriptional responses to S.
What does Thioglucosidase do?
Thioglucosidase activity (increased by S-deficiency) liberates S for recycling for example in glucosinolates
What regulates sulphur uptake and assimilation rates?
Local sulfate levels
OAS
Reduced sulphur (glutathione, Cys etc)
Light, carbon, nitrogen reserves, cicadian rhythms etc
What regulates SULTR genes?
Transcriptional, post-transcriptional and post translational/ allosyeric regulation of transporters
What regulates ATP sulfurylase and APS reductase?
Transciptional regulation of ATP sulfurylase and APS
What regulates Cys synthase?
Allosteric interactions and metabolic regulation
When Sulphur is low what happens to SULTR?
They are up regulated to assimilate more sulphur
What genes are down regulated in low sulphur levels?
Some of them are:
MAM1
MAML
BCAT
What is the name of the toxic sulphur defence found in Brassicas?
The ‘mustard oil bomb’ contains glucosinolate break down products
How is the ‘mustard oil bomb’ produced?
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
What is the consequence of stricter sulphur laws?
Less sulphur enters soils and plants are more prone to sulphur deficiency which can be augemented with sulphur fertilizers like elemental sulphur
What are key facts about Phosphorus?
The 11th most abundant element
5th most abundant element in a plant
1st or 2nd most limiting nutrient
What is the role of Phosphorus for plants?
Roles in cell structure, energy and information storage and energy and information transfer
What are the biomolecules that phosphorus found in?
DNA, RNA, Membrane phospholipids, Bones/Teeth and phosphorylation (signalling)
What form is phosphorus assimilated as?
Phosphate which depending on the pH is H2PO4^-, HPO4^2- and PO4^3-
What is the phosphorus cycle (preindustrial)?
Slow weathering of rocks
Terrestial cycle (assimialtion, then eaten finally ending up as manure or decomposing)
Slow leaching to lakes and oceans
Sedimentation
Upwelling
What are the impacts on the phosphorus cycle since global industrialisation?
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)
What is accumulation factor?
The degree of enrichment required in plant cells compared to the environment
What is the accumulation factor for the macronutrients?
P - 6000
N - 50
K - 30
S - 10
Ca - 5
Mg - 5
Why is phosphorus insoluble when in soil?
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
What is Labile P?
Amount or proportion of any P that is readily liberated from a phosphate-containing compound by hydrolysis
How much more phosphate is moved now than natural (pre-agricultural era)?
4 times
What happens to phosphate avaliablity when pH changes?
5.5 to 7 pH optimum
Below 5.5: Fixation by Fe, Al, Mn
Above 7: Fixation as calcium phosphates
What happens to phosphate used in agriculture?
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
What was the consequence of not understanding P fixation?
Overuse of fertilizer (N:P of 1.5:1)
What is the ratio of N:P now in agriculture?
N:P
6:1
What is eutrophication?
Increased biomass production (algal blooms)
Decrease O2 concerntrations
Ecosystem collapse
What happens to chlorophyll when there is low P?
Decreased production of cholrophyll leading to decrease in dry mass
Where does nutrient uptake take place?
Uptake across the plasma membranes of root cortex or endodermal cells
What can plasma membranes do to help the plant uptake the right nutrient?
Selectivity of which nutrients are absorbed by the cortex and endodrmis
How many families of plant phosphate transporters are there?
3
What is the function of plant phosphate transporter 1?
Pht1 localised in the plasma membranes
H+/PO4^3- co transporters that acquire Pi from the rhizosphere
12 membrane-spanning domains
Where is PHt 2 located?
Chloroplast
Where is PHt located?
Mitochondria
What is the function of PHt?
Uptake P at root/soil interface and translocation within the plant
Where are most PHt 1 expressed?
Root tissues
How many PHt1 genes do Arabidopsis have?
9
How many PHt1 genes do rice have?
13
How many PHt1 genes do poplar have?
12
What is the relationship between mycorrhiza and PHt 1?
Some PHt 1 are mycorrhiza inducible
What is Rhizosphere?
Microzone that is around plant roots and is influenced by chemicals released by plant
What chemicals impact the Rhizosphere?
Sugars
Mucilage
Phenolics
Organic acids
Phosphatases
How do many species respond to to nutrient defiencies?
They release H+ and organic acids
Why do plants released acids and protons into the soil?
Low pH helps to solubilise these nutrients, which otherwise would be bound to soil particles and be unavaliable
What are carboxylates?
Citrate, malate and malonate
Why are carboxylates released into the soil?
The carboxylates released into soil form complexes to the metal cations bound to phosphate. This releases phosphate by ligand exchange
Why are protons also released along with carboxylates?
To balance the ionic charge
How much of soil Pi is bound to organic P?
30-80%
What root traits are associated with enhanced phosphate uptake?
Reduced gravitropism
Increased formation and elongation of lateral roots and root hairs
Aerenchyma (air spaces that allow metabolically inexpensive growth), particularly in aquatic plants)
What does low P promote in roots?
Low P promotes shallower roots, enabiling the plant to exploit the higher P concerntrations near the soil surface
What is the advantage of root ‘foraging’?
Enables plants to rapidly colonise nutrient-rich pathches of soil
Important when xploiting immobile nutrients
Also beneficial for NO3^-, when plants are in competition
What are root hairs?
Small hair like extensions of the epidermis of the root in which water-filled soil pores that would be inaccessible to roots
Which cells do root hairs extend out of?
Specilised trichoblast cells
What do root hair cells do?
Increase surface area
Increase nutrient depletion zone
How does P deficiency impact root hairs?
Increases root hair lengths and density
What are the advantages of tapping into the mycorrhizal fungi?
Increase effective reach of their roots
How many plants have a symbiotic relationship with mycorrhizal fungi?
80% (roughly)
How long ago did the plant mycorrhizal fungi relationship form?
450+ mya
Why is it believed that this relationship formed?
Surrogate roots for first land plants
What is the main role of the symbiotic relationship?
Thought to be phosphate uptake
Which plants can’t form this symbiotic relationship?
Arabidopsis and other Brassicaceae
What forms in plant cells as a result of the arbuscular mycorrhizal fungi relationship?
Fungal arbuscules
What is the internal structure when this relationship happens?
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
What form is the Pi translocated?
As a polyphosphate
Which symbiotic relationships can legumes form?
With both rhizobia and AM fungi
How does the AM fungi, plant symbiotic relationship form?
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
