Plant Bio 4; Maintaining World Food Production

Question 1

What is a herbicide?

Answer 1

Used to kill unwanted plants/specific weeds in a crop/plantation
Nonselectively clear waste ground, industrial sites, railways and rail embankments

Question 2

How do herbicides affect key processes for plant growth?

Answer 2

Growth regulation
Cell division
Photosynthesis

Question 3

What is amino acid biosynthesis in the case of glyphosate?

Answer 3

When you spray roundup on a weed and it’s absorbed throughout the plant, where it prevents the plant from making its own food

Question 4

Can dead weeds regrow after roundup?

Answer 4

No, roundup breaks down over time into natural materials and won’t move

Question 5

What 4 things can herbicides interfere with?

Answer 5

General growth regulation
Cell division
Photosynthesis
Amino acid synthesis

Question 6

What is general growth regulation?

Answer 6

Plant hormone 2, 4 D (ocuxin)
Crops (in grasses)- not affected
Weeds destroyed (broadleaf)

Question 7

What is cell division that herbicides interfere with?

Answer 7

Oryzalin block microtubules formation

Affects plants only

Question 8

What is photosynthesis that herbicides can interfere with?

Answer 8

Altrazin= blocks the electron transport chain

• photosynthesis is shut down
• pollution of ground water

Question 9

What is amino acid synthesis that herbicides can interfere with?

Answer 9

Glyphosate (round up)
Interferes with aromatic amino acid synthesis (trp, tyr, phe)
Round up ready plants

Question 10

What is a non-selective herbicide?

Answer 10

Glyphosate

Question 11

What can glyphosphate do?

Answer 11

Kill all plants - but there’s a development of crops resistant to glyphosate for agricultural use

Question 12

What does roundup inhibit?

Answer 12

EPSPS, an enzyme in the chorismate pathway (which competes with PEP)

Question 13

What is the aromatic amino acid synthesis pathway?

Answer 13

Shikimate 3-phosphate + PEP

Via EPSPS

5-enopyruvylshikimate-3-phosphate

To aromatic amino acids

Question 14

What is the idea of a plant resistant to glyphosate?

Answer 14

EPSPS-resistant to glyphosate, still binding to PEP (ie mutagenesis)

Question 15

How do you get an EPSPS not binding glyphosate?

Answer 15

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

Question 16

Idea of engineering a crop resistant to glyphosate?

Answer 16

Discovery of an enzyme resistant to glyphosate

Plant transformation using T-DNA

Question 17

What is a promoter in the T-DNA for a roundup ready plant?

Answer 17

35S promoter; constitutive or specific to growing tip

No need for a selectable marker gene

Question 18

What do round up ready crops use?

Answer 18

An EPSPS gene from agrobacterium, highly expressed in growing tips

Question 19

Examples of roundup ready plants?

Answer 19

Soybean 
Corn 
Cotton 
Potatoes 
Canola 
Alfalfa

Question 20

Advantages of round up ready genes?

Answer 20

Safer herbicide than alternatives (atrazine)
Single application post-emergence- reduced use
Promotes “no till agriculture”, reduced soil losses

Question 21

Possible disadvantages of roundup ready genes?

Answer 21

Higher circulating herbicide concentrations in plants

Question 22

What is bacillus thuringiensis?

Answer 22

Many different bacterial isolates
Multiple specificities against different insect groups (esp Lepidoptera, coleptera)
Biological role in bacterial life cycle unclear

Question 23

What is bacillus thuringiensis proposed as?

Answer 23

A mode of action of cry toxins

Question 24

How would a BT toxin work?

Answer 24

1. Crystal is ingested by the larvae and is solubilised in the midgut of the larvae at pH 12 (alkaline pH) to release protoxin
2. Proteolytic cleavage of the protoxin into an activated toxin
3. Binding to a receptor in membrane of epithelial cells in the midgut of the larvae;
   - leads to the opening of channels
   - larvae will die

Question 25

What is the promoter in BT?

Answer 25

Leaf specific

Question 26

Second part of LB segment for BT?

Answer 26

CRY

Question 27

RB segment of BT gene?

Answer 27

Promoter ; 35S
Second part; HyR, KanR
EPSPSR

Question 28

What is the crop with highest pest incidence/spray usage?

Answer 28

Cotton

Question 29

What is BT corn targeted against?

Answer 29

Corn borer

Corn root worm

Question 30

Advantages of BT insect resistance?

Answer 30

Reduced pesticide usage
Safer pesticide
Resistance to BT
non target organisms a reported to be higher in crops