Corn Fungus Is Nature's Master Blaster

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Source: Duke University

Date: 2005-07-26

http://www.sciencedaily.com/releases/2005/07/050726074532.htm

Corn Fungus Is Nature's Master Blaster

DURHAM, N.C. -- Biologists have discovered that a common corn fungus

is by far nature's most powerful known cannoneer, blasting its

spores out with a force of 870,000 times the force of gravity.

Farmers need not worry about being nailed by a fungal supergun,

however. The infinitesimal spore travels only two-tenths of an inch

(5 millimeters) before plummeting.

The analysis of the fungal shooting ability led the biologists to

determine that the osmotic pressure from potassium, and not the

mannitol, likely generated the force necessary for the powerful

blast. (Credit: Frances Trail)

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Related section: Plants & Animals

Nevertheless, said the biologists, the fungus Gibberella zeae

outguns the previous record holder, the fungus Pilobolus, by almost

a hundred-fold. It also outperforms a rifle, which launches its

bullet with less than one-tenth that acceleration.

The researchers -- Frances Trail and Iffa Gaffoor of Michigan State

University, and Vogel of Duke University -- published their

findings in the June 2005 issue of Fungal Genetics and Biology. The

study was supported by the U.S. Department of Agriculture and the

Michigan Agricultural Experiment Station.

According to Vogel, the " bioballistics " of the fungus offers a

dramatic lesson in the physics of scaling. At the infinitesimal

scale of the fungus' spore, atmospheric drag plays an enormous role -

- hence the need for an extremely high ejection speed to achieve

even the most modest dispersal of its spore.

" To get a literal feel for a world in which drag makes more impact

than does gravity, just inflate a six-inch balloon and throw it as

hard as you can, " said Vogel.

The purpose of the study that revealed the fungus's extraordinary

launch capabilities was to better understand the biological

mechanism behind the fungal supergun. Basically, the gun is powered

by the buildup of pressure inside the spore-containing fungal

fruiting body, called the perithecium, due to the ability of sap to

create an osmotic pressure. Such pressure is due to water flowing

across a membrane into the perithecium as it tries to equalize the

concentration of a salt solution inside the chamber. In the case of

the fungus, at question was whether the sugar mannitol or potassium

ions were responsible for the osmotic pressure that generated the

propulsive force.

In their experiments, Trail and Gaffoor created a fungal " shooting

gallery " consisting of a small glass chamber, in which they mounted

a block of gel-like agar containing mature perithecia. They arranged

the agar so that the perithecia would launch their spores onto a

removable glass cover slip. The researchers measured the length of

the fungal blasts and calculated the mass of the spore. That mass

turned out to be very low for a fungal spore, explaining why the

fungus could achieve such extraordinary launch speeds, said Vogel.

He fed data from the laboratory experiments and spore mass

calculations into a computer program he had developed to determine

the ballistics of such projectiles. One result was the record

acceleration of 870,000 times gravity for the spores and a launch

speed of nearly 80 miles an hour.

The analysis of the fungal shooting ability led the biologists to

determine that the osmotic pressure from potassium, and not the

mannitol, likely generated the force necessary for the powerful

blast.

Vogel said he originally created the bioballistics program to

demonstrate to his undergraduate classes how drag and other factors

affect the trajectories of natural projectiles -- from kangaroo rats

to locusts to fleas to fungal spores.

" The big animals aren't so interesting in terms of drag, " said

Vogel. " But when you get down to a flea, it loses about eighty

percent of potential range to drag. And the optimum launch angle

gets lower. In physics class, people are taught that the best angle

is forty-five degrees, but when drag is bad, the angle needs to be

lower -- you want to achieve some distance while you still have

decent speed. Altitude no longer gives much advantage. Thus, in the

fungus the launch angle is barely above horizontal, " he said.

" An obvious question is why the fungus even bothers. Given the short

range of its spores, why bother accelerating to eighty miles per

hour to go a mere five millimeters?, " said Vogel. " Since there is

almost no air movement at the surface where the spore grows, the

real object of the launch is to get the spore even a little ways

from the parent, so that it can get into air currents, which will

really give the spore some range. "

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This story has been adapted from a news release issued by Duke

University.