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.
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
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
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
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.