Lecture 14 - insecticides and herbicides Flashcards
what lead to recent decrease in pesticide usage
DTT accumulation and subsequent harm to birds of prey
where Bt found first
silk worm
what is the Bt toxin
the spores have crystal like protein structure called Cry
which has the insecticidal Bt toxin
where is Bt toxin activated
only in mid gut of insect
gets cleaved to activate the prototoxin
what 2 domains in Bt toxin
pore-forming domain =makes gut permeable
recpetor binding domain = bind o receptor in gut
why does Bt need to be put in another bact - p.flourescens
toxins are unstable and break down rly fast
only lasts a few days
but in new bact - stays stable
how to express the Bt toxin in plants
but the bacterial gene in front of 35S promoter (strong promoter)
advantages of Bt corn
More effective pest control
Lower rates of disease
Higher yields
what are some porblems with conventional herbicides
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
what is the herbicide u need to know bout
glyphosate
what pathway does glyphosate target
shikimate pathway
produces aromatic amino acids and other important metabolites in plants
what exactly does glyphosate act on
inhibits EPSP synthase
advantages of glyphosate
- kills everything
- rare resistance
- doesnt persist - environmentally more better
- vry specific to plants only
what bacteria used to find initial resistance gene
salmonella
what mutation came from salmonella thats used to give resistance to glyphosate and how
AroA
alters EPSP synthase gene
how is AroA put into plants
put gene in from o f strong promoter
so whole plant is resistance cuz every cell expresses gene
why was AroA not good enough
had low affinity
idek what to
what gene was found that works better than AroA
CP4 from agrobacterium
has high affinity (low Km)
why was GOX gene isolated and used in plants with CP4
CP4 is good but glyphosate accumulates in the plants
so GOX allow it to be metabolsied into glycine
what crop is good example of use of all the glyphosate stuff
transgenic soyabean
disadvanatgaes of transgenic soyabean
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
advantages of transgenic soyabean
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
