Re: What happens to a plant in a vacuum?

You are correct that without oxygen and carbon dioxide, plants could not 
survive in space. However, to grow plants in a space station you have to grow 
the plants in an enclosed area so the oxygen and carbon dioxide could be 
retained and recycled. The more serious problem seems to be lack of gravity. 
Plants depend on gravity (termed gravitropism) to orient themselves so shoots 
grow "up" and roots grow "down." Rapid distribution of gases outside the plant, 
drainage of water from soil, and plant hormone movement within the plant also 
depend on gravity. Deficiency of rootzone oxygen often occurs  in plants 
growing in the space station because of lack of gravity to cause water to drain 
from the soil.The solution to that problem may be to grow plants without soil 
in hydroponics or solution culture.

There have been many experiments where plants have been grown on the space 
station. In a 1997 experiment wheat grew and flowered but produced no seed. The 
reason for lack of seed was not immediately known but later work showed that 
lack of gravity to promote buoyancy-driven convective air movement  limited the 
supply of carbon dioxide  to leaves. 

Plant seeds have survived in the vacuum of space with little or no harmful 
effects. In April, 1984, NASA sent 12.5 million tomato seeds into space and 
retrieved them in January, 1990. Many of the seeds were sent to school children 
so they could germinate them. A slightly higher percentage of seeds from space 
germinated than earthbound control seeds, and almost all produced normal 
plants. 

An internet report says China has a major program of exposing seeds to space 
environments and finding improved varieties due to exposure to space radiation. 
This report seems questionable given the minimal success of radiation breeding 
studies on Earth. 

The American Society for Gravitational and Space Biology website has lots of 
info on plants in space.


References


Spaceflight Plant Growth


Seeds in Space


Space wheat yields no seeds


China Expands Space Breeding Program Using Recoverable Satellites


Brassica Seeds Fly on Mir


American Society for Gravitational and Space Biology