Plant Bio 4; Maintaining World Food Production Flashcards
What is a herbicide?
Used to kill unwanted plants/specific weeds in a crop/plantation
Nonselectively clear waste ground, industrial sites, railways and rail embankments
How do herbicides affect key processes for plant growth?
Growth regulation
Cell division
Photosynthesis
What is amino acid biosynthesis in the case of glyphosate?
When you spray roundup on a weed and it’s absorbed throughout the plant, where it prevents the plant from making its own food
Can dead weeds regrow after roundup?
No, roundup breaks down over time into natural materials and won’t move
What 4 things can herbicides interfere with?
General growth regulation
Cell division
Photosynthesis
Amino acid synthesis
What is general growth regulation?
Plant hormone 2, 4 D (ocuxin)
Crops (in grasses)- not affected
Weeds destroyed (broadleaf)
What is cell division that herbicides interfere with?
Oryzalin block microtubules formation
Affects plants only
What is photosynthesis that herbicides can interfere with?
Altrazin= blocks the electron transport chain
- photosynthesis is shut down
- pollution of ground water
What is amino acid synthesis that herbicides can interfere with?
Glyphosate (round up)
Interferes with aromatic amino acid synthesis (trp, tyr, phe)
Round up ready plants
What is a non-selective herbicide?
Glyphosate
What can glyphosphate do?
Kill all plants - but there’s a development of crops resistant to glyphosate for agricultural use
What does roundup inhibit?
EPSPS, an enzyme in the chorismate pathway (which competes with PEP)
What is the aromatic amino acid synthesis pathway?
Shikimate 3-phosphate + PEP
Via EPSPS
5-enopyruvylshikimate-3-phosphate
To aromatic amino acids
What is the idea of a plant resistant to glyphosate?
EPSPS-resistant to glyphosate, still binding to PEP (ie mutagenesis)
How do you get an EPSPS not binding glyphosate?
EPSPS present in bacteria
Bacteria are sensitive to glyphosate
Mutagenesis on bacteria
Looking for bacteria growing on glyphosate
Clone the gene encoding for a resistant version of EPSPS= EPSPSR gene
Idea of engineering a crop resistant to glyphosate?
Discovery of an enzyme resistant to glyphosate
Plant transformation using T-DNA
What is a promoter in the T-DNA for a roundup ready plant?
35S promoter; constitutive or specific to growing tip
No need for a selectable marker gene
What do round up ready crops use?
An EPSPS gene from agrobacterium, highly expressed in growing tips
Examples of roundup ready plants?
Soybean Corn Cotton Potatoes Canola Alfalfa
Advantages of round up ready genes?
Safer herbicide than alternatives (atrazine)
Single application post-emergence- reduced use
Promotes “no till agriculture”, reduced soil losses
Possible disadvantages of roundup ready genes?
Higher circulating herbicide concentrations in plants
What is bacillus thuringiensis?
Many different bacterial isolates
Multiple specificities against different insect groups (esp Lepidoptera, coleptera)
Biological role in bacterial life cycle unclear
What is bacillus thuringiensis proposed as?
A mode of action of cry toxins
How would a BT toxin work?
- Crystal is ingested by the larvae and is solubilised in the midgut of the larvae at pH 12 (alkaline pH) to release protoxin
- Proteolytic cleavage of the protoxin into an activated toxin
- Binding to a receptor in membrane of epithelial cells in the midgut of the larvae;
- leads to the opening of channels
- larvae will die
What is the promoter in BT?
Leaf specific
Second part of LB segment for BT?
CRY
RB segment of BT gene?
Promoter ; 35S
Second part; HyR, KanR
EPSPSR
What is the crop with highest pest incidence/spray usage?
Cotton
What is BT corn targeted against?
Corn borer
Corn root worm
Advantages of BT insect resistance?
Reduced pesticide usage
Safer pesticide
Resistance to BT
non target organisms a reported to be higher in crops
