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Herbicides Flashcards

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1
Q

How much is spent on herbicides a year

A

$30 million

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2
Q

What are the problems with herbicides

A

Require a difficult regime
Need to be time perfectly
Kill Untargeted plants and organisms
Bad for the environment

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3
Q

What’s the ideal herbicide

A

Kill weeds directly without affecting any other plant

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4
Q

What is Atrazine?

A

Herbicide used against broadleaf weeds, used in maize farming.
2nd most popular herbicide
76 million applied each year
Invented in 1958

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5
Q

What’s the molecular action of Atrazine

A

Binds to plastoquinone-binding protein in photosystem II

Plants die from starvation and oxidative damage caused by breakdown in the electron transport process

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6
Q

What was the lawsuit in regards to Atrazine

A

2014 there was a report that levels in water lead to reproductive issues in fish.

Law suit against Syngenta due to concerning levels in water
Had to pay $105 million to reimburse more than 100 water suppliers

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7
Q

What is glyphosate

A

Used to kill plants by farms
Kills all plants no specificity
Effective and cheap
Introduced in 1974 by Monsanto

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8
Q

What’s the molecular action of glyphosate

A

Inhibits the plant enzyme EPSP synthase, an enzyme not present in animals

The EPSP synthase is responsible for the biosynthesis of the aromatic amino acids
Phenylalanine
Tyrosine
Tryptophan

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9
Q

What is round up ready?

A

Crops which are transgenetically resistant to glyphosate

Introduced in 2007

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10
Q

What was the glyphosate usage increase between 1996 and 2012

A

10 fold increase

15 million to 159 million pounds

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11
Q

How can plants be transgenically modified to detoxify atrazine

A

Atrazine binds to the photosynthetic electron transport protein PSBA
Detoxification can be achieved by overexpression of gluthione-S-transferase
Conjugated to atrazine and marks it for degradation

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12
Q

How are roundup ready crops resistant to glyphosate

A

The modified expression of ESEP
Glyphosate binds and inhibits the enzyme ESEP synthase
The ESEP synthase enzyme usually produces EP3P which is the precursor for aromatic amino acids
Modified ESEP is not recognised by the glyphosate and still have normal ESEP function therefore can produce amino acids

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13
Q

What is the modification in modified EPSP

A

The gene is obtained from agrobacterium CP4
Glyphosate binds to EPSP in a non-inhibitory manner
There is a mutation in active site ALA to GLY in codon 100

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14
Q

What’s the % of crops in the US which are roundup ready crops

A

87% soybeans
61% cotton
26% corn

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15
Q

Give an example of an alternation to the target herbicide resistant

A

Sulfonyl Urea is a herbicide that binds to ALS which blocks the synthesis of amino acids leucine, isoleucine and valine

Resistance is achieved by expressing a variant with ALS which isn’t recognised by the inhibitor

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16
Q

What’s an insecticide and why are they needed

A

A substance used to kill insects

One of the main carriers of virus (also create wounds which all fungi to grow)

Kill and eat plants

Over $8 billion market

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17
Q

What are the disadvantages of insecticides

A

Toxic compounds can that need to be handled carefully

Need to be supplied locally to reduce ecosystem effects

Negative effects to whole ecosystem

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18
Q

What does Bt stand for

A

Bacillus thuringiensis

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19
Q

What is the Bt toxin ?

A

Found in gram positive bacterium

During spore formation the bacteria produces crystals of proteins which are called cry and cryt

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20
Q

What is the cryt toxin group

A

A group of delta endotoxins
There are over 700 cryt genes sequence that encore for the delta endotoxins
They are selectively toxin to insects

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21
Q

What are the highly conserved cyt toxin families

A

Cryt1, 2 and 3

Each are highly specific and to target insects

Toxic to insects at concentrations as low as 50ng

Extremely popular with maize and cotton

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22
Q

How can the cry protein be toxic to insects

A

Crystal inclusions which contain Cry1a gene are infested and dissolved

The alkaline lime activate the protein by proteolytic cleavage by proteolytic enzymes

Cleaving turns cry proteins into smaller protease resistant toxic polypeptides

Bind specifically to receptors on the surface of midgut epithelial cells

Pores become permeable to inorganic ions, amino acids and sugars

Cause cell death which results in the insect dying

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23
Q

Why are bt toxins a bad herbicide

A

Can be stored for Atleast a year

Field half life ranges from 0.5-4 days

Sunlight alone or in combination with high ph and rain can inactivate there toxin

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24
Q

What is Bt maize

A

Transgenic maize with the Bt toxin gene

Highly effective and specially targets insects which feed on the plants

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25
Q

Process on how to make by trangeneic maize

A

The maize genome is G and C rich unlike the bacillus genome therefore the bt toxin gene (648 amino acid) was resynthesised in vitro to become more G and C rich without changing the protein (amino acid code)

New DNA is transferred into vecotors which can transform plant cells (T. a isn’t very effective therefore bindery vector may be more efficient)

Introduce into immature cells via bombardment (gene gun) — hard to grow cereals like maize therefore careful sterile conditions need to be undertaken

Transgenic cells are selected using the herbicide

Plants are grown (undifferentiated ball of callus with excess hormones like auxins and cytokinins)

26
Q

Why did the EU oppose the introduction of bt maize

A

Because the bacterium used to transform the plasmid into the plant contain an penicillin resistant gene for selection therefore they didn’t want this gene to be released

27
Q

What are the two public alarms for by maize??

A

Monarch butterfly fiasco

Starlink fiasco

28
Q

Highlight key factors in the monarch butterfly fiasco

A

Popular butterflies
Larvae eat milk weed which is planted near gm maize
Fear the transgenic pollen from by maize could kill the butterfly
Uproar after a scientist did a test which dusted milkweed leaves with bt pollen and found the larvae grew less and had lower survival rates
Very wide spread via media
People were in uproar — people jumped behind it, easier to believe the bad

There was a “field test” in 2000 which tried to address validity issues. Involved collecting pollen on plotted plants places in cornfields and provided it solely to larvae

Not really a field study

29
Q

What did scientist say about the monarch butterfly fiasco

A

Validity was questioned
- unrealistic time think that the larvae would just eat off the pollen covered milkweed
The field test wasn’t a real field test as most of it was done in the lab and no other environmental factors were taken into consideration

2001: Naranjo at al found
Minor negative effects observered in Bt crops compared with alternative insecticides was actually Lower
Little overlap between the monarch breeding season and timing of pollen shed
Only 10% of monarch butterfly breed in range of cornfields
Eggs are laid underneath
Only one pollen variation contains enough bt toxin to kill larvae
EPA concluded the butterflies were less at risk from Bt corn than conventional corn due to insecticide usuage

People are still against

30
Q

What is the starlink fiasco

A

Starlink is corn approved for livestock production (not human) (due to the bt toxin not being digested immediately — a trait of an allergen)

An environmental group and a company called “genetic ID” used PCR technology on taco shells in the US

Found minor presence of Bt toxin — causes massive panic with people calling they were having allergic reactions

Caused for a massive recall of over 300 products that may contain the corn as well as a massive compensation of $60 million to Taco Bell from Kraft Food for loss of sales due to taxi containing bt

31
Q

What really happened in starlink

A

Further analysis found the presence of the Cry gene however no protein was detected (no detection when proved with antibodies)

28 people reported to have an allergic reaction
17 people submitted blood
0 allergies were detected

Just mass panic

32
Q

Why was bt transgenic maize needed

A

Corn borer butterfly (an example)
Adult lay eggs on the underside of the leaf
Insecticides can’t reach
3-4 of infestation can occur in single growing season
Eggs located internally therefore can’t be reached by chemically (=more insecticide are used)
cause millions £ in damage

33
Q

What are outcomes of bt maize

A

2009 bt maize was planted in more than 22.2 million hectares
$3.2 billion saved for maize growers
Study in 2018 showed that the br corn had protected nearby fields of non-Bt corn reducing insecticide usage

In New Jersey insecticide amount decreased 85%

34
Q

Has there been a political connection with bt transgenic crops?

A

In 2001 an Indian seed company sold insect resistant cotton

Was later discovered they were using transgenic bt cotton ( not approved in India)

Recall of all seed and all plants destroyed

Massive uproar
People demanded them to come back
This fast tracked gm approval in India

35
Q

What are mycotoxins

A

Toxins produced by fungi (get into plants from insects feeding)

Mycotoxin accumulation can be carcinogenic and toxic to humans and animals

Particularly devastating in developing countries, warmer climate encourage fungi growth

36
Q

What is Alfatoxin

A

Toxin produces by fungi

Most potent chemical liver carcinogenic

Characterised by haemorrhage a cute liver damage and depending on severity death

People infected with hep A and C are 10 fold more likely to get liver cancer

37
Q

What is Fumonisins

A

Produced by fungi
Reduces uptake of folate In different cell lines
Fatal to animals like horses because it affects their nervous system
Consumption while pregnant can lead to implications

38
Q

What is ochratoxin

A

Labelled as a carcinogen and a nephrotoxin

Linked to rumours in the urinary tract

39
Q

How can virus spread through plants

A 
Mostly transmitted by insects 
Can spread 
Organ to organ 
Cell to cell via plasmodesmata 
Generation to generation
40
Q

Why is it hard for plants to create a defence mechanism against viruses?

A

Virus RNA is constantly evolving due to lack of RNA polymerase
Constantly produced mutations = new strains

41
Q

What is cross protection

A

Protection conferred on a host by inoculation with one strain or component of a microorganism that prevent infection when challenged with a similar strain

A mild virus can protect a plant against a more severe strain

42
Q

When was cross protection first demonstrated

A

In 1929 by McKinney
Observed in tobacco plants
Infected plants with light green strain or tobacco mosaic virus (TMV) the appearance was yellow symptoms after re-inculcation with a more severe strain of TMV was we repressed

Known as interference — gene silencing mechanism. In animals there’s a similar mechanism called RNAi

43
Q

What is an example of successfully cross protection

A

Hawaiian papaya industry

Papaya industry was disrupted by the time papaya ringspot virus (PRSV)

Caused massive devastation to the country

Cross protection gave plants resistance to the virus (picture)

44
Q

How can gene silencing be achieved?

A

Achieved by introducing dsRNA which can’t be turned into a protein (antisense or co-suppression) into the cell.

It is cleaved by the ribonuclease called DICED-2.

This forms short interfering RNA (siRNA) which are usually 21-25 nt long

Enzyme called Argonaute will remove on strand on the dsRNA and use the remaining one as a guide strand

The guide siRNA binds with a complex called RISC (RNA induces silencing complex)

The siRNA/RISC complex interacts with the guide rna homologous mRNA

The RISC cleaves the mRNA

45
Q

What does (p)TGS

A

Post transcriptional gene silencing

46
Q

What is an antisense construct

A

Gene silencing technique— found that injecting antisense construction lead to gene silencing (but how? PTGS)

Antisense construct are viral RNA genome constructs made the wrong way round

Inverted dsRNA

Can hybridise you the sense RNA (complementary) and creates a translationally inactive double strand RNA molecule n

Strong p35s promoter and terminator sequence

47
Q

What is co-suppression

A

The introduction of sense and antisense construct was found to have higher gene silencing efficiency

Accumulation of antisense and sense Observed in several plant PTSG systems

48
Q

What’s hpRNA and what’s the relevance to gene silencing

A

HairpinRNA

Have been found to be more effective at gene silencing

49
Q

What’s an microbial pathogen

A

Induced by insects

Fungus

Currently controlled by fungicides and breeding for resistance

50
Q

What’s the hypersensitive reliance

A

When part of the plant which is being infected initiated programmed cell death

51
Q

What are PAMPS

A

Pathogen associated molecular patterns

Produced by Fungal infection can start the hypersensitive reaction

52
Q

What are AVR

A

Fungal avirulence proteins

Interact with plant resistant proteins

53
Q

Describe the interaction between AVR and R

A 
AVR = fungal avirulence proteins 
R = plant resistance protein

a successful interaction between them will trigger the hypersensitive response in plants

Gene to gene interaction

Highly polymorphic due to an evolutionary arms race. Constantly evolving — some species have over 200 different R genes

If interaction is unsuccessful then fungus can invade plant

54
Q

Describe R proteins

A

Plant resistant proteins
Can be primary (membrane bound) or secondary (cytosol)

Combined to signalling domain
Protein kinase
Coiled coil
Nucleotide binding

55
Q

What happens when hypersensitive response is triggered (before cells die)

A

Produce antimicrobal compounds

Phytolexins
Antifungal enzymes
Hydrogen peroxide

56
Q

What is a successful pathogen ?

A

AVR-R interaction is incompatible
Successful infection
Can also secrete effectors you suppress the resistance further

57
Q

What are the complex R-AVR interactions

A

AVR genes are recognised by multiple R gene

One AVR Is suppressed by another AVR gene by interaction with one R gene

2 co-operating R genes both necessary to recognise 2 AVR

58
Q

What are the classes of R genes

A

Cell surface LRR containing R genes
Anchored to PM

Nucleotide binding and leucine rich repeat receptors
Multiple domain which allows for simultaneous recognition

59
Q

How can the microbial system apply to viral infections ??

A

Similar response

Use endogenous resistant protein (Rx)
Contain leucine rich repeat
Conformational change in the protein results in a signal transduction pathway involving w Ran GTPase

Leads to virus inactivation

60
Q

What fungus caused potato blight

A

Phytophthora infestans

61
Q

What genes were identified to be resistant to potato blight which one was the most resistant

A

RGA 1,2,3,4

RGA 2

Genetics (6 decks)

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