Healthy soil and sustainable growing

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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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