Herbicides GMOs

Commercial reasons Ht crops were adopted so rapidly:

- Seed/biotech companies could sell more of their herbicide by also selling seeds that required the use of the herbicide - Seed/biotech companies acquired more and more of the germplasm that had been available to small breeding companies and included Ht in this germplasm - These herbicides were more efficacious and safer than older herbicides

Scientific reasons herbicide-tolerant crops were adopted so rapidly

- The mode of action of these herbicides was well understood - Bacteria resistant to these herbicides had been identified - Plants resistant to these herbicides had been identified in the laboratory and/or field - This was a single gene trait for resistance - These genes were non-plant in origin - The herbicides used in biotech crops were much more efficacious and safer than older herbicides

There are 3 strategies for engineering herbicide resistance in plants. (with Glyphosate)

1-Over expression of the target protein (gene) 2-Mutation of the target protein 3-Detoxification of the herbicide in the crop species

What is a good target for a herbicide?

Any biochemical pathway in a plant that is not in humans. This makes the biochemical pathways in chloroplasts especially attractive

the most widely used herbicides in the world

Atrazine

Why must farmers plan next years crops before using Atrazine?

Atrazine has carryover to the next year

What the side effect of Atrazine?

Atrazine takes months to break down once it is applied. It also can make it to the water table under the right soil conditions.

Glufosinate • Also called phosphinothricin (PPT) • Sold under the name Basta, Rely,

Broad-spectrum herbicide • Most effective against broadleaf weeds (dicots) whereas glyphosate is more effective against grasses and perennials but both are still non-selective herbicides

Soil bacteria do not have chloroplasts so the bacterial EPSP synthase gene did not contain the?

DNA sequence that coded for the plant transit peptide.

What is Glufosinate derived from?

Derived from a natural product, Bialaphos, a tripeptide

Glufosinate Inhibits

Glutamine synthase (GS) which is important in N assimilation. Glufosinate treated plants die due to a buildup of ammonia and a cessation of photosynthesis.

Detoxification.

Glyphosate, like many herbicides, can be degraded by soil microorganisms. An oxidoreductase cleaves a C-N bond forming two compounds that are or can be converted to normal plant metabolites.

How does Atrazine work?

It binds to plastoquinone-binding protein in photosystem II, which animals lack.

Why is 2,4-d still used today?

It is a low cost herbicide and continues to be used today.

Is 2,4-d selective or non-selective?

It is a selective herbicide in that it controls broadleaf weeds. It is absorbed through the leaves and is translocated to the meristems resulting in uncontrolled growth, leading to stem curlover, leaf withering, and eventual plant death

How does overexpression work ?

The increased level of protein was due to amplification of the gene in the cultures (20 copies)

Detoxification of the herbicide in the crop species.

This strategy requires the identification and overexpression of a protein that will inactivate the herbicide - Cytochromes P450 are a good example of detoxification enzymes

Mutation of the target protein.

This strategy requires that a protein (gene) is identified with which the herbicide can no longer bind

Overexpression of the target protein (gene).

This strategy titrates out the herbicide such that there remains some protein to carry out normal metabolic processes

How does Expression of a mutant form of EPSPS?

This version of EPSP synthase has a slightly altered amino acid sequence from that found in plants. The alteration prevents glyphosate from binding, while still allowing the resistant EPSPS to catalyze amino acid synthesis reactions.

What accounts for 1/3 of loss in potential yeild ?

Weeds , unwanted plants, along with pests and diseases

2,4-D

a synthetic plant hormone used on corn and other cereal crops to kill broad-leaf weeds.

Chloroplasts: synthesize

all of an animals' essential amino acids. phenylalanine, tryptophan and tyrosine

The shikimate metabolic pathway is used by?

bacteria, fungi, algae, parasites and plants for the biosynthesis of aromatic amino acids (phenylalanine, tyrosine, and tryptophan). pathway not found in humans

Non-selective herbicides kill all plant material and are used to

clear waste ground, industrial sites, railways and railway embankments. Also used when the agricultural plant is resistant to the herbicide

Before 1960 weeds were generally controlled by ?

cultural practices.

What is the good thing about Dicamba?

dicamba breaks down to very simple substances like carbon dioxide and water

Why is Atrazine use controvesial?

due to widespread contamination of drinking water and associations with birth defects and menstrual problems when consumed by humans at concentrations below government standards - banned in the European Union

The CP4 EPSPS gene was engineered for plant expression by

fusing the 5' end of the gene to a chloroplast transit peptide derived from the petunia EPSPS

The plasmid used to move the gene into soybeans contained the mutant EPSPS gene from Agrobacterium and a

gene encoding beta-glucuronidase (GUS) from Escherichia coli as a marker.

Dicamba acts by

increasing plant growth rate. At sufficient concentrations, the plant outgrows its nutrient supplies, and dies

Glyphosate's mode of action is to

inhibit an enzyme (EPSPS) involved in the synthesis of the aromatic amino acids: tyrosine, tryptophan and phenylalanine. Glyphosate binds more tightly (2300x) to EPSPS than PEP

Herbicides, or weed killers, are substance used to

kill unwanted plants.

For corn, Monsanto uses a

mutated corn gene isolated from corn tissue culture that was selected for glyphosate tolerance.

Dicamba is

non-selective

Is Atrazine selective or non selective?

non-selective

Is Glufosinate on selective or non-selective

non-selective herbicide

Is Glyphosate (round up) selective or non- selective?

non-selective weed control • broad-spectrum systemic herbicide used to kill weeds, especially perennials; kills 76 of the world's worst 78 weeds

How is herbecide resistance identified?

of a protein that no longer binds the herbicide. The activity of many herbicides has been found to result from inhibition of a single protein (gene).

The DNA was injected into the soybeans using the

particle bombardment method. The expression of the GUS gene was used as the initial evidence of transformation.

The best herbicides are

plant-specific. In the U.S., herbicides account for about 70% of all agricultural pesticide use

Glutamine synthase is located in?

plastids in green tissues and cytosol in roots

What is a good thing about Glufosinate?

readily biodegradable with a half-life in soil of 3-20 days

15+ weed species have been confirmed as

resistant to glyphosate.

Why is it useful to combine Detoxification and and the mutatnt gene?

so that glyphosate does not accumulate in the plant

Selective herbicides kill

specific targets while leaving the desired crop relatively unharmed

The construct used in Monsanto's dicotyledonous biotech crops - soybean, oilseed rape and cotton - still contains

the Agrobacterium mutant EPSPS, chloroplast transit peptide, CaMV 35S promoter and 3' nos

The transit peptide is required for

the enzyme to be transported to the chloroplast, the location of the shikimic acid pathway.

What are good things about Round up?

• decomposes very rapidly and only kills plants in which it makes contact; sometimes need to use Atrazine in combination • most widely used herbicide in the US

Glyphosate is known as?

• sold under the brand name Roundup by Monsanto