Herbicides Flashcards
Tilling negatives and positives?
Gets rid of weeds, fairly low labour
Can degrade soil quality in surface nutrients and produce more run off
What is the loss of profit due to weeds growing in Australia?
3.3 Billion dollars $ in expenditure and loss
Main types of pesticides and herbicides used?
Glyphosate (round up), atrazine, Acetochlor (all herbicides US)
Side effect of Sinox (earliest developed herbicide?) and method for this?
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
Issues faced with herbicides?
Minimise- resistance
mammalian toxicity
persistance in environment
How does atrazine function?
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
How come atrazine doesnt affect crops?
Only specifically affects broadleaf leaves
How is maize resistant to atrazine?
Contains soluble enzyme glutathione transferase that can detoxify the molecule of atrazine by binding to glutathione. no longer can affect photosystem 2.
What is another effect of atrazine?
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.
How are weeds now resistant?
Mutation in psbA gene from SER->GLY changes D1 protein now meaning the affinity to atrazine is lowered.
How does glyphosate function?
Intefers with shikimate pathway that results in three major amino acids (tryp, tyr, phenol). Stops EPSP synthase adding EPSP to 3-phosphate-shikimate.
Why is this not dangerous for humans?
Since this pathway is not present in humans, it is not dangerous for us.
Where did scientists isolate the gene for glyphosate resistance from?
From bacteria (agrobacterium) in 1983. It has a different shaped EPSP enzyme that does not get inhibited by glyphosate.
Construct for soybean resistance to glyphosate
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)
What was the error spotted 6 years after release of round up resistance?
Cheeky inversion as a result of tDNA process.
What is the danger of glyphosate?
Not yet proven to be cancer causing but lawsuits exist against monsanto
IAA stands for?
Indol acetic acid (auxin) growth hormone
How is it used as a herbicide?
Doesn’t affect humans. Can spray and tell plants to grow uncontrollably.
What had to be adjusted in IAA to make it a good herbicide?
Make it more stable.
What was agent Orange and what was its purpose?
2,4 D Auxin analogue - to kill all trees in the Vietnam war. It had side effects resulting in dioxins that affected birth defects.
What is put into crops to make it resistant to 2,4 D?
Enzyme AAD - discovered in soil bacteria - detoxifys 24D
Describe construct for 2,4D resistance
Ubi10 (constant) promoter, aad gene from soil bacteria, selectable marker (pat).
How can roundup and 2,4D be used together?
Make plants with double resistance that you can then alternate between herbicides and stop other crops.
