Don't look for any forests or gardens to sprout in space, but scientists are interested in the effect of growing plants and trees in a gravity-free environment. Such information could prove invaluable to any future plans to grow food on a manned space station.
On Earth, it might lead to more nutritious agricultural products or aid industrial processes such as the production of paper.
The two-week delay in the launch, and the lower-than-planned orbit of Challenger due to an engine failure, have adversely affected a few of the experiments aboard. But at this writing, the shuttle crew was still scheduled to stay aloft for the planned seven days. As part of the mission, the astronauts are studying the growth of mung beans, oats, and pine seedlings in space. Preliminary results are that the plants are growing fine.
In particular, the crew is testing the effect of zero gravity on the formation of lignin, a natural polymer in plants that binds cells together and gives them the mechanical support to grow upward.
Lignin is something of a hero in the plant world. Not only is it responsible for the woody structure of trees, but it also provides resistance to decay, repels water, and acts as an antibiotic.
Yet the compound does have a few irksome traits. It can't be digested by humans, so it reduces the use of certain plants as food. It also burns up considerable energy derived from photosynthesis during its formation in plants.
Thus, if a way could be found to control the formation of lignin, such as under ``microgravity'' conditions, theoretically, more energy would be available for the production of edible compounds in plants. This could lead to better food products.
Lignin is also a nuisance for paper companies. They have to get rid of the substance when extracting cellulose to make paper. Reducing the proportion of lignin in trees from its current level of about 25 percent could make their jobs easier.
On the shuttle flight, scientists aren't thinking about these down-to-earth applications; they are just trying to better understand lignin's chemistry, and learn more about how plants perform in space.
``We just have very little information about how plants grow and behave in space,'' says Dr. Joe Cowles, a scientist at the University of Houston who devised the experiment.
The plant growth tests are among 13 experiments, most of them in astronomy, scheduled to take place during this third flight of Spacelab, a set of scientific hardware built by the European Space Agency that is cradled in the cargo bay of the shuttle.
In the plant experiments, astronauts are tending 96 pine seedlings, some about one inch high and the others four inches high. Their growth and lignin formation will be compared with seedlings grown on the ground. Scientists will also probe the effects of zero gravity on mung bean and oat seeds.
Tests on an earlier shuttle flight showed a substantial reduction in the lignin content of mung beans but relatively little in pine seedlings. Hence the reason for further tests.
Scientists will also be interested in any other insights they might glean about the arcane world of space-based botany. To date, few plants have gone into space. Researchers are curious, for instance, about how roots grow in the absence of gravity. On earlier flights, some roots have grown upward, which would affect how future space-station gardeners tended them.
Not much is known, either, about how plants germinate in orbit. The Soviets are ahead of the United States here: They have sent up a plant that went through an entire life cycle.
But as planning for a manned US space station picks up, the interest in how plants perform in such an environment, both for its terrestrial and space applications, is expected to grow.
``We are just at the beginning of what should be an exciting time in this area,'' says biologist Allan Brown of the University of Pennsylvania.