15270_herbicide res

8/7/2019 15270_herbicide res

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WEED Vs PLANT

Weed compete with crop plants for :

Nutrients

Moisture Light

Weeds cause decline in yield and quality ofplants.


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Classes of herbicides

Several classes of herbicides:

Glyphosate (Roundup ready)

Phosphinothricin

Chlorsulfuron, Imazapur,

Bromoxynil,

Atrazine

These are quite effective for broad spectrum

weed control.


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Herbicide resistance strategy

Three approaches have been followed to obtain herbicideresistant transgenic plants:

(1) modification of the plant enzyme or other sensitive

biochemical target of herbicidal action to render itinsensitive to the herbicide.

(2) overproduction of the unmodified target proteinpermitting normal metabolism to occur even in the

presence of the herbicide(3) introduction of an enzyme or enzyme system to

degrade and/or detoxify the herbicide prior to itsaction.


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The RoundUp Ready Story

Glyphosate is a broad-spectrum herbicide

Active ingredient in RoundUp herbicide

Kills all plants it come in contact with

Inhibits a key enzyme (EPSP synthase) in an amino acid pathway

Plants die because they lack the key amino acids

A resistant EPSP synthase gene allows cropsto survive spraying.


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Action of Glyphosate

Glyphosate (Roundup ready) is absorbed

through foliage.

translocated to growing point (meristem part).So it affect mostly growing plants.

It inhibit Shikimate pathway-synthesis of

chorismate.

Chorismate are utilized in further cycle to

synthesize aromatic amino acid. (Trp,Tyr,Pha)


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+ Glyphosate

X

RoundUp Sensitive Plants

X

X

Shikimic acid + Phosphoenol pyruvate

5-Enolpyruvyl shikimic acid 3-phosphate

(EPSP)

Plant

EPSP synthase

Aromatic

amino acids

Without amino acids,

plant dies

X


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Bacterial

EPSP synthase

Shikimic acid + Phosphoenol pyruvate

3-enolpyruvyl shikimic acid-5-phosphate

(EPSP)

Aromatic

amino acids

RoundUp Resistant Plants

+ Glyphosate

With amino acids, plant

lives

RoundUp has no effect;

enzyme is resistant to herbicide


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Final TestConsumer Acceptance

RoundUp ReadyCorn

Before After


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Isolation of gene

Eventually, naturally occurring glyphosate-tolerant microbes were identified, including

Agrobacterium sp. strain CP4,Achromobactersp.

strain LBAA, and Pseudomonas sp. strain PG2982The enzymes isolated from these bacteria EPSPsynthases.

Other EPSP synthases isolated from Gram-

positive bacteria, including pathogenic speciessuch as Streptococcus pneumonia andStaphylococcus aureus.


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35S promoter

(CMV)EPSPS(Agrobacterium)

Transform cotton cells in culture, plasmidinserts in genome

Grow cells in presence of antibiotic

Regenerate plant from transformed cells

Test protein levels and glyphosate resistance

Ti PlasmidTi PlasmidAmpr

(ampicillin

resistance)

Ampr

(ampicillin

resistance)

ReplicationoriginReplicationorigin

Multiple

cloning

site

Multiple

cloning

site

Ti PlasmidAmpr

(ampicillin

resistance)

Replicationorigin

Multiple

cloning

site

Roundup-ready cotton, soybeans - Monsanto

See ECB 10-40


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Transgenic crops

Wheat

Cotton

Tobacco

Tomato

Soybeans

Corn


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Phosphinothricin (PPT or 'Basta') is anotherbroad spectrum herbicide

which acts by inhibiting the synthesis ofglutamine synthase (GS) enzyme involved inassimilation of ammonia produced by nitratereduction.

Amino acid catabolism and photorespiration.In the absence of this enzyme, ammoniatoxicity damages the plants.

Phosphinothricin resistant


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Introduction of alfalfa GS gene regulated by 35Spromoter was effective in producing PPT toleranttobacco plants.

These plants regenerated at 20 times the lethalconcentration of PPT but showed severe damagewhen sprayed at four times the normal fieldapplication of the herbicide.

The tissue from the transgenic plants showedoverproduction of GS enzyme and 7-fold lowerlevel of free NH3 relative to the control tissue butgrew and reproduced normally.

15270_herbicide res

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