Drought Resistant GM Rice Toxic?

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24 Sep 2004 18:06:03 -0000

 

Drought Resistant GM Rice Toxic?

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ISIS Press Release 24/09/04

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Drought Resistant GM Rice Toxic?

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Prof. Joe Cummins explains why one method to genetically

engineer drought resistant rice could be perilous for human

and animal health

 

References for this article are posted on ISIS members'

website. membership details www.i-sis.org.uk/membership.php

 

Commercial genetic engineering has been based on inserting a

single transgene along with control elements into a crop

plant. Traits such as herbicide tolerance, insect resistance

and virus resistance have been commercialized without much

understanding of the metabolic consequences of the

alterations.

 

To deal with more complex and agriculturally significant

traits, a technique called metabolic engineering has been

developed [1] to retune endogenous metabolic pathways.

 

Recently, transgenic rice modulated in the polyamine

biosynthetic pathway has been found to be drought tolerant

[2, 3]. Polyamines are carbon chains containing two or more

amine (NH 2 ) groups. Polyamines are essential compounds

found in all living cells. They increase as bacteria putrefy

animal flesh, producing a strong rotting odor. Polyamines

are given names such as putrescine and cadaverine or

spermine and spermidine. Even though the polyamines are

essential for cell growth, they may also cause disease in

animals.

 

In animals and fungi, putrescine is the precursor of

spermidine and spermine ; it is synthesized from the amino

acid ornithine. Plants have an alternative pathway that

converts the amino acid arginine to putrescine, using the

enzyme arginine decarboxylase (ADC) , the product of the adc

gene. This is followed by additional reactions to form

spermidine and spermine using S-adenosylmethionine and the

action of the enzyme S-adenosylmethionine carboxylase

(SAMDC), the product of the Samdc gene.

 

Rice plants were transformed with the ADC gene from Datura

(Jimson weed, a traditional and commercial source of drugs),

driven by the maize ubiquitin promoter and the first intron;

and transcription was terminated with the Agrobacterium nos

transcription terminator. The transgenic rice plants had

elevated basal levels of putrescine, that were further

elevated during drought stress, leading to enhanced

production of spermidine and spermine by increased SAMDC

enzyme.

 

The exact mechanism by which increased putrescine increases

drought resistance is not fully understood but it is clear

that elevated putrescine levels activate spermidine and

spermine synthesis that, in turn, regulate putrescine

production and sets in motion the resistance to stress [2,

3]. The transgenic rice is designed to provide sustainable

rice production under stress conditions.

 

Stress resistant rice has been reported without reference to

the potential impact of the metabolic alteration – such as

increase in polyamines - on mammals consuming the transgenic

rice. Polyamines are known to be elevated in the cells and

body fluids of cancer patients. Drugs inhibiting the

synthesis of polyamines can prevent cancer and have been

used in cancer treatment [4].

 

Moreover, polyamines can give rise to toxic products.

Spermidine and spermine can be metabolized to hydrogen

peroxide, ammonium and acrolein, which are toxic to cells .

Polyamines can contribute to the suppression of immunologic

reactions in the lung [5]. Polyamines are implicated as

uremic toxins leading to renal failure [6]. Chicken feed

containing elevated amines, such as putrescine, performed

poorly and caused a condition called " necrotic cellular

debris " [7]. Wines may contain elevated polyamines from

grape must and fermentation. It is believed that spermidine

and spermine may be beneficial in wine while putrescine and

cadaverine are linked to symptoms such as nausea, sweating

and difficult breathing [8].

 

The good-news message that transgenic rice may be grown

under drought conditions should be tempered by the bad-news

that eating the transgenic rice may make one quite ill. The

promotion of this transgenic crop along with others in the

scientific journals seems invariably to neglect the

potential adverse effects of the crop on humans and wild

life. Open field trials should not be undertaken in the

absence of proper risk assessment and toxicity tests.

 

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