Herbicides

Question 1

Tilling negatives and positives?

Answer 1

Gets rid of weeds, fairly low labour

Can degrade soil quality in surface nutrients and produce more run off

Question 2

What is the loss of profit due to weeds growing in Australia?

Answer 2

3.3 Billion dollars $ in expenditure and loss

Question 3

Main types of pesticides and herbicides used?

Answer 3

Glyphosate (round up), atrazine, Acetochlor (all herbicides US)

Question 4

Side effect of Sinox (earliest developed herbicide?) and method for this?

Answer 4

Respiratory uncoupler binds to H atoms in intermembrane space and passes straight through membrane. This means the gradient of electrons cannot build during respiration and no ATP can form

Question 5

Issues faced with herbicides?

Answer 5

Minimise- resistance
mammalian toxicity
persistance in environment

Question 6

How does atrazine function?

Answer 6

Binds with D1 protein and hence competes with plastoquinone which is a shuttle for electrons in photosystem 2. It normally is reduced by D1 then passes on electron but when this cannot occur, starvation and oxidative damage TO PLANTS ONLY

Question 7

How come atrazine doesnt affect crops?

Answer 7

Only specifically affects broadleaf leaves

Question 8

How is maize resistant to atrazine?

Answer 8

Contains soluble enzyme glutathione transferase that can detoxify the molecule of atrazine by binding to glutathione. no longer can affect photosystem 2.

Question 9

What is another effect of atrazine?

Answer 9

Mimicks eostregon (endocrine disruptor) can have low birthrate effects and affect sex of animals. Long half life (up to 261 days) means it can have lasting effects.

Question 10

How are weeds now resistant?

Answer 10

Mutation in psbA gene from SER->GLY changes D1 protein now meaning the affinity to atrazine is lowered.

Question 11

How does glyphosate function?

Answer 11

Intefers with shikimate pathway that results in three major amino acids (tryp, tyr, phenol). Stops EPSP synthase adding EPSP to 3-phosphate-shikimate.

Question 12

Why is this not dangerous for humans?

Answer 12

Since this pathway is not present in humans, it is not dangerous for us.

Question 13

Where did scientists isolate the gene for glyphosate resistance from?

Answer 13

From bacteria (agrobacterium) in 1983. It has a different shaped EPSP enzyme that does not get inhibited by glyphosate.

Question 14

Construct for soybean resistance to glyphosate

Answer 14

35s promotor Nos terminator cp4 EPSP gene Plastid targetting sequence to get into chloroplast (requires n terminal targetting sequence to guide to port to chloroplast)

Question 15

What was the error spotted 6 years after release of round up resistance?

Answer 15

Cheeky inversion as a result of tDNA process.

Question 16

What is the danger of glyphosate?

Answer 16

Not yet proven to be cancer causing but lawsuits exist against monsanto

Question 17

IAA stands for?

Answer 17

Indol acetic acid (auxin) growth hormone

Question 18

How is it used as a herbicide?

Answer 18

Doesn’t affect humans. Can spray and tell plants to grow uncontrollably.

Question 19

What had to be adjusted in IAA to make it a good herbicide?

Answer 19

Make it more stable.

Question 20

What was agent Orange and what was its purpose?

Answer 20

2,4 D Auxin analogue - to kill all trees in the Vietnam war. It had side effects resulting in dioxins that affected birth defects.

Question 21

What is put into crops to make it resistant to 2,4 D?

Answer 21

Enzyme AAD - discovered in soil bacteria - detoxifys 24D

Question 22

Describe construct for 2,4D resistance

Answer 22

Ubi10 (constant) promoter, aad gene from soil bacteria, selectable marker (pat).

Question 23

How can roundup and 2,4D be used together?

Answer 23

Make plants with double resistance that you can then alternate between herbicides and stop other crops.