Lecture 14 - insecticides and herbicides

Question 1

what lead to recent decrease in pesticide usage

Answer 1

DTT accumulation and subsequent harm to birds of prey

Question 2

where Bt found first

Answer 2

silk worm

Question 3

what is the Bt toxin

Answer 3

the spores have crystal like protein structure called Cry
which has the insecticidal Bt toxin

Question 4

where is Bt toxin activated

Answer 4

only in mid gut of insect
gets cleaved to activate the prototoxin

Question 5

what 2 domains in Bt toxin

Answer 5

pore-forming domain =makes gut permeable
recpetor binding domain = bind o receptor in gut

Question 6

why does Bt need to be put in another bact - p.flourescens

Answer 6

toxins are unstable and break down rly fast
only lasts a few days

but in new bact - stays stable

Question 7

how to express the Bt toxin in plants

Answer 7

but the bacterial gene in front of 35S promoter (strong promoter)

Question 8

advantages of Bt corn

Answer 8

More effective pest control
Lower rates of disease
Higher yields

Question 9

what are some porblems with conventional herbicides

Answer 9

Hard to distinguish very similar species
Require more than one type of herbicide
Poor environmental properties e.g. persistence, or kills other things
Used as pre-emergence sprays (wasteful if weeds werent gonna grow anyway)
Broad based resistance

Question 10

what is the herbicide u need to know bout

Answer 10

glyphosate

Question 11

what pathway does glyphosate target

Answer 11

shikimate pathway
produces aromatic amino acids and other important metabolites in plants

Question 12

what exactly does glyphosate act on

Answer 12

inhibits EPSP synthase

Question 13

advantages of glyphosate

Answer 13

• kills everything
• rare resistance
• doesnt persist - environmentally more better
• vry specific to plants only

Question 14

what bacteria used to find initial resistance gene

Answer 14

salmonella

Question 15

what mutation came from salmonella thats used to give resistance to glyphosate and how

Answer 15

AroA
alters EPSP synthase gene

Question 16

how is AroA put into plants

Answer 16

put gene in from o f strong promoter
so whole plant is resistance cuz every cell expresses gene

Question 17

why was AroA not good enough

Answer 17

had low affinity
idek what to

Question 18

what gene was found that works better than AroA

Answer 18

CP4 from agrobacterium
has high affinity (low Km)

Question 19

why was GOX gene isolated and used in plants with CP4

Answer 19

CP4 is good but glyphosate accumulates in the plants
so GOX allow it to be metabolsied into glycine

Question 20

what crop is good example of use of all the glyphosate stuff

Answer 20

transgenic soyabean

Question 21

disadvanatgaes of transgenic soyabean

Answer 21

No increase in yield
May still have some toxicity
Reliance on one herbicide lead to spread of glyphosate-resistance
Supply in small number of large companies

Question 22

advantages of transgenic soyabean

Answer 22

Used pre- or post- emergence
Only need to be sprayed when required
Decreased tillage, less erosion

Other herbicides at least 3X as toxic and persist in the environment twice as long

also less expensive, more money