[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[SANET-MG] poisonous seeds



August 18, 2004

Prof. Joe Cummins

“Making rice drought resistant by enhancing polyamines: poisonous seeds?”

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). Endogenous metabolic pathways have begun to be tuned to
achieve significant and far reaching agricultural modifications.
Recently transgenic rice modulated in the polyamine biosynthetic pathway
have been found to be drought tolerant.(2,3). Polyamines are carbon
chains containing two or more amine (NH2) groups, Polyamines are
essential compounds found in all living cells. The polyamines increase
as bacteria putrefy animal flesh producing the 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, as will be discussed below.

In animals and fungi, putrescine is the precursor of spermidine and
spermine , it is synthesized from the aminoacid 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, followed by additional reactions to form spermidine and
spermine using S-adenosylmethionine and the action of enzyme
S-adenosylmethionine carboxylase (SAMDC) the product of the Samdc gene.
Rice plants were transformed with the Datura ADC gene (Dadc) driven by
the maize ubiquitin promoter and first intron and transcription was
terminated using the Agrobacterium nos transcription terminator . The
transgenic rice plants had elevated basal levels of putrescine and that
level was elevated during drought stress leading to enhanced production
of spermidine and spermine by the SAMDC enzyme which was elevated by
activation of the samdc gene.. 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 sythesis that regulate putrescine production and sets in motion
the resistance to stress (2,3). The transgenic rice are 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, including elevated levels
of polyamine, on mammals consuming the transgenic rice. Polyamines are
elevated in the cells and body fluids of cancer patients. Drugs which
inhibit synthesis of polyamines can prevent cancer and can be used in
cancer treatment (4). Polyamines possess an important intrinsic
toxicity. Spermidine and spermine can be metabolized to hydrogen
peroxide, ammonium and acrolein which can cause cellular toxicity.
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 consuming feed containing elevated amines ,
such as putrescine, performed poorly and had 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 very ill. The promotion of this transgenic crop along
with others using scientific journals seems negligent in neglecting the
potential adverse effects of the crop. Field test releases of drought
resistant rice should be done with great care to avoid spreading the
hazardous genes to crop and weedy rice.

References

  1. Capell,T. and Christou,P. Progress in plant metabolic engineering
     2004 Current Opinion in Plant Biotechnology 15,148-54
  2. Capell,T.,Bassie,L. and Christou,P. Modulation of the polyamine
     biosynthetic pathway in transgenic rice confers tolerance to
     drought stress 2004 Proc. Natntl. Acad. Sci. USA 101,9909-14

3. Capell,T. Enhanced drought tolerance in transgenic rice August 2004
http://www.isb.vt.edu/news/2004/news04.aug.html#aug0402

4. Bachrach,U. Polyamines and cancer:Minireview article 2004 Amino Acids 26,

307-9

5. Hoet,P. and Nemery,B. Polyamines in the lung: polyamine uptake and
polyamine linked pathological or toxicological conditions 2000 Am. J.
Physiol.Lung Cell Mol. Biol. 278,L417-33

6. Sakat,K,Kashiwagi,K,Sharmin,S,Ueda,S,Irie,Y, Murotani,N. and
Igarashia,K. Increase in putrescine, amine oxidase, and acrolein in
plasma of renal failure patients 2003 Biochemical and Biophysical
Research Communications 305,143-9

7. Tamim,N,Bennett,L,Shellem,T. And Doer,J. High-Performance Liquid
Chromatographic Determination of Biogenic Amines in Poultry Carcasses
2002 J.Agric. Food Chem. 50,5012-15

8. Herberger,K,Csomos,E. and Simon-Sarkadi,L. Principal Component and
Linear Discriminant Analyses of Free Amino Acids and Biogenic Amines in
Hungarian Wines 2003 J.Agric. Food Chem 51,8055-60

********************************************************
To unsubscribe from SANET-MG:
1- Visit http://lists.sare.org/archives/sanet-mg.html to unsubscribe or;
2- Send a message to <listserv@sare.org> from the address subscribed to the list. Type "unsubscribe sanet-mg" in the body of the message.

Visit the SANET-MG archives at: http://lists.sare.org/archives/sanet-mg.html
For more information on grants and other resources available through the SARE program, please visit http://www.sare.org.