2-Plants: War on plants necessary to feed the hungy?
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-------------------------------- GENET-news --------------------------------
TITLE: 'Gene gun' blazes away in biotech fight on famine
SOURCE: Reuters, by Jeremy Smith
DATE: November 14, 2001
------------------ archive: http://www.gene.ch/genet.html ------------------
FEATURE - 'Gene gun' blazes away in biotech fight on famine
LONDON - A designer "gene gun" blasting slivers of metal into an innocent
soybean plant may sound like a futuristic and far-fetched way to ward off
famine by improving the food supply of the world's poorest countries. So
does subjecting stalks of defenceless corn to doses of high-voltage
electricity, or bombarding them with sound waves. But these are just some
of the techniques used by scientists striving for more versatility in
altering plant cell structures in the controversial research area known as
biotechnology, which tries to improve on the precision of natural plant
Their efforts, they hope, will eventually help the world's poor guard
against starvation by beating crop disease and beefing up yields of staple
foods such as soya, wheat and maize. While the bulk of current research
aims to improve food plants, the rest of the work is concerned with non-
food crops such as cotton, tobacco, ornamental plants and pharmaceuticals.
Even though the term biotechnology refers to a wide range of technologies
making use of living organisms, it has now become largely synonymous with
genetic engineering - the controlled alteration of genetic material, or
DNA, by artificial means. Genetic modification (GM) involves exchanging or
splicing genes of unrelated species that cannot naturally swap with each
other and scientists say the applications are almost limitless.
The species can be vastly different, for example, inserting scorpion toxin
or spider venom genes into maize and other food crops as a 'natural
pesticide' to deter insects and birds from feeding on them, or fish
antifreeze genes into tomatoes. Gene-splicing has also been used to
overcome the sensitivity of fruits such as bananas and melons to lower
temperatures so that they can be grown in colder parts of the world. And
scientists believe that plants can be genetically altered to grow cheap
vaccines inside them, leading to the use of fruit for painless and
plentiful protection against disease.
But how does genetic engineering of plants actually work?
SCIENTISTS USE VARIETY OF GENE-SPLICING TECHNIQUES
Scientists now have a number of techniques at their disposal to move genes
artificially into host organisms although only a small proportion of the
target cells in the selected plant ever properly incorporate the desired
DNA. One of the most successful ways is to use 'agrobacterium', a soil-
dwelling bacterium, as a go-between to introduce genetic information into
more than 100 plant species, mainly into wide-leafed plants such as tomato,
apple and pear. A wide variety of plant and tree varieties have been
altered by this method, and the technique was used to modify the first
genetic plants ever produced - tobacco, petunia and cotton. When the
bacterial DNA is integrated into a plant chromosome, it effectively hijacks
the plant's cellular machinery to ensure that the bacterial population
"GENE GUN" BLASTS PLANT WITH SLIVERS OF METAL
But the most important cereal crops are not affected by agrobacterium and
so other methods had to be found. Scientists say their relative success
rates are still difficult to judge. These include ballistic impregnation,
also known as "bioballistics" or "biolistics", an unlikely-sounding
projectile science developed and popularised during the 1980s and used for
narrow-leafed plants such as grasses and grains.
A specially-designed "gene gun" fires dozens of metal slivers like bullets
at target cells. The tiny pellets, usually of tungsten or gold, are much
smaller than the diameter of the target cell, and coated with genetic
material. While the shell cartridge is stopped in its tracks by a
perforated metal plate, the metallic micro-missiles are able to penetrate
into living cells where the genetic material is then carried to the nucleus
to be integrated among the host genes. Gene guns have helped to transform
monocot species such as corn and rice. Monocots, meaning monocotyledonae or
plants with one cotyledon or seed leaf, comprise a quarter of all flowering
plant types. Barley and wheat also derive from monocots.
"Biolistics became quite popular, while the other ways of directly
introducing DNA were there all the time but didn't take off quite so much,"
said Professor Peter Caligari at the Department of Agricultural Botany at
Reading University, in southern England. "The monocots, for example the
grasses and cereals, were much more difficult to transform using the
popular agrobacterium system of transferring DNA than the dicots. But
biolistics was a way of getting at the monocots," he told Reuters.
Biolistics was still used moderately widely though probably still less than
the agrobacterium approach, now developed to be more readily used with at
least some of the monocots, he said.
"Agrobacterium at first was fairly limited to dicotyledons although they
had also got it to work for monocotyledon plants like corn. But it
(biolistics) is just easier," said Jane Rissler, senior scientist at the
Union of Concerned Scientists, a prominent U.S. environmental group.
PLANTS BLASTED WITH HIGH VOLTAGE, SOUND WAVES
Other transfer methods include creating pores or holes in the cell membrane
to allow entry of the new genes. This can be achieved chemically, with
sound waves or by using electric currents - a technique known as
electroporation. With strong electric pulses transmitted on a microsecond
basis, minute pores are caused in the plant cells which allows the desired
DNA to enter from a surrounding solution. Sometimes, a genetic scientist
will wish to 'silence' a particular gene of an organism to prevent it from
being expressed. Gene silencing was first used to create tomatoes with a
higher solid content and longer shelf life by halting the natural evolution
of an enzyme involved in the ripening process.
Viruses can also be a useful DNA vehicle as they are infectious particles
to which a new gene can be added, carrying this gene into a recipient cell
while infecting that cell. And where the host cell is large enough, a fine-
tipped glass needle may be enough to inject genetic material containing the
new gene, although fewer cells can be treated in this way and the method is
much more time-consuming than using a gene gun.
"There's always the thought that maybe a more efficient or more widely
applicable single system is out there somewhere," said Reading University's
Caligari. "And the more knowledge we get about things, the more possible
that perhaps becomes," he added.
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