'Gene gun' blazes away in biotech fight on famine

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'Gene gun' blazes away in biotech fight on famine JoAnn Guest

Aug 10, 2002 16:56 PDT

5) 'Gene gun' blazes away in biotech fight on famine

 

By Jeremy Smith

 

LONDON (Reuters) - 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 defenseless 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 breeding.

 

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 soy, 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 proliferates.

 

" 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

popularized 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.

 

08:27 11-14-01

 

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