Observatory: Pushy, Pushy, Pushy

January 6, 2004
By HENRY FOUNTAIN

Parasites are pushy creatures, invading their hosts in one way or another. The golden nematode, a parasite that invades tomato and potato plants, takes pushiness to an extreme, penetrating a host plant at a rapid rate (about two minutes per cell layer).

Now, scientists in the Netherlands and Scotland may have discovered the secret to its speed. The nematode is pushy in a novel way: it produces proteins that make plant cell walls loosen up as it moves in.

The proteins, a type called expansins, had previously been identified only in plants. They induce the cell walls to extend and relax and are thought to play a role in both plant growth and the disassembly of cell walls. Although the precise details of their function is not known, they weaken bonds between a wall's cellulose fibrils and compounds called glucans that hold the fibrils together.

The researchers identified a nematode gene responsible for the proteins and showed that they were produced in a juvenile stage of the parasite, by esophageal glands. Their research was reported in the journal Nature.

Many organisms that get their food from plants use enzymes called glycanases to break down cell walls completely. The researchers found that golden nematodes produce glycanases, too, at the same time that they produce the expansins.

The researchers suggest that by loosening up the walls, the expansins make the wall's component parts more accessible to the glycanases. So the plant tissue is broken down faster and the parasite can enter sooner.

Hydrogen's Hurdles

All the talk of a future economy based on hydrogen fuel is well and good, but there are many technological hurdles to overcome, not the least of which is figuring out how to store all that explosive gas efficiently and safely.

Liquefying hydrogen for storage is energy intensive because it must be cooled to about minus 425 degrees Fahrenheit. And since there is no practical way to keep a storage container that cold, boil-off is a problem.

It can be kept at room temperature as a compressed gas, but much less hydrogen can be stored in a given volume this way.

A new solution has been proposed by scientists at the University of Chicago and the Carnegie Institution of Washington. They suggest storing hydrogen molecules in tiny ice cages.

Specifically, they write in The Proceedings of the National Academy of Sciences, hydrogen could be stored in a network of frozen water molecules that has a crystalline structure, known as a clathrate. Gas molecules are trapped in cavities within the crystal and help stabilize it.

Clathrates, also known as gas hydrates, occur in nature, under the seafloor and in Arctic permafrost, for instance, where they trap immense amounts of methane. But the researchers synthesized their own, using hydrogen as the trapped gas.

The researchers found that their clathrate could exist at about minus 320 degrees under normal pressure. Then, when the clathrate was warmed to about minus 200, the hydrogen would be released.

Minus 320 degrees might not seem like much of an improvement over minus 425, but in fact a clathrate at the higher temperature could be kept cold through the use of liquid nitrogen. The researchers say that much more work remains - for one thing, other clathrates may be more effective - but that the approach is promising.

Next Stop, Mercury

All eyes may be on Mars these days, but NASA engineers also have their sights set on Mercury, the innermost planet. The agency's first mission to orbit it is scheduled to lift off in May, and the spacecraft, known as Messenger, has been undergoing reliability tests.

Messenger will take images of Mercury's surface and conduct other studies when it reaches the planet in 2009.