Humanity may be a long way from harvesting tomatoes in outer space, but researchers now have a better idea of how plants might grow in such zero gravity conditions.

Researchers from the University of Florida in Gainesville grew seedlings of Arabidopsis thaliana (also called thale cress) on the International Space Station (ISS) to see how the weightless conditions of outer space would affect root growth. Scientists cultivated the plants in specialized growth units and photographed them every six hours; their root patterns were compared with similar plants grown on the ground at NASA's Kennedy Space Center in Florida.

The researchers expected that the roots would grow away from a light source (as they do in soil on the ground), and the ISS experiment confirmed that light acts as a primary determinant in root-growth patterns. But the scientists also measured the diagonal paths or "skewing" of the roots, as well as their "waving," the undulating wiggles and curves that growing roots normally exhibit as a means of avoiding obstacles like rocks. 

Roots apparently don't need gravity to orient their directional skewing. They'll grow away from a light source regardless of gravitational forces. Waving, however, is significantly different in outer space, and the ISS roots curved and waved through their growth medium in a subtler pattern than they would have on Earth.

Though plants on Earth do use gravity to help determine their direction of growth, "it is clear that gravity is neither essential for root orientation, nor is it the only factor influencing the patterns of root growth," wrote lead authors Anna-Lisa Paul and Robert Ferl in the Dec. 2012 issue of the journal BMC Plant Biology.

"It seems that other features of the environment are also required to ensure that a root grows away from the seed, thereby enhancing its chances of finding sufficient water and nutrients to ensure its survival."