Plants harness energy from the Sun through the process of photosynthesis, which converts light energy into chemical energy. Plants then store this chemical energy within their molecular bonds as sugar. To fuel photosynthesis, plants need light, water, and carbon dioxide. Sunlight isn’t the only light that can fuel photosynthesis. Scientists have been experimenting with how to grow plants under “artificial” conditions in space using light-emitting diodes (LEDs) instead.
The chlorophyll within plants absorbs red and blue light. (Chlorophyll can’t absorb green light; that’s why green light passes through to our eyes when we look at plants.) Scientists have discovered that some plants need only red light for photosynthesis, so NASA is experimenting with using red LEDs to grow plants in a lab.
“Tropisms” are growth movements living organisms have toward certain external stimuli. Plants on Earth have three tropisms: phototropism, geotropism, and hydrotropism. These refer to plants’ responses to light, gravity, and water. In a space-based lab, each of these tropisms presents a challenge. The need for light can be solved with color-specific LEDs, but since gravity conditions in space are very different that they are on Earth, scientists are experimenting to figure out how to grow plants that can orient themselves in space. Blue light, though not crucial for photosynthesis, does seem to provoke plants to grow in specific directions and with specific morphology. Watering plants in space presents an engineering challenge that scientists are still solving. Here on Earth, water flows “down” so it’s easy for plants to “capture” water in the dips and crevices of their leaves. In fact, many plant adaptations evolved to help plants gather and hold water as it drops, flows, or falls. In the microgravity of space, though, water must be delivered to the plants so it gets continuously absorbed, or else it would just float away.
In their explorations of growing plants in space, scientists are paying special attention to plants with high antioxidant levels. Antioxidants are chemical substances that protect human cells against free radicals, which are potentially damaging molecules formed during the breakdown of certain foods in the digestion process, during exposure to radiation, and during other physical processes. Scientists believe free radicals play a role in cancer, heart disease, and other illnesses, so allowing astronauts to grow an especially healthy “space garden” could be beneficial during a long trip into space.