Photosynthesis Experiment and System Testing and Operation (PESTO) - 07.15.14
ISS Science for Everyone
Science Objectives for Everyone Studied the photosynthetic response of plant tissues grown in microgravity. Results can lead to the development of regenerative life support systems on future missions to the Moon or Mars.
Science Results for Everyone
Add “farmer” to job functions of future space travelers, who will likely produce oxygen and purify water using plants. With that in mind, the PESTO investigation finds that microgravity alters leaf development, plant cells, and chloroplasts (cell structures that conduct photosynthesis), but is not harmful to the plants. Dwarf wheat plants on the ISS grew 10 percent taller than those on Earth, although leaf growth rate was very similar in both.
Dynamac Corporation, Cape Canaveral, FL, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
December 2001 - June 2002
Previous ISS Missions
ISS Expedition 4 was the first mission for the BPS hardware.
- PESTO studied the effects of microgravity on wheat (renewable source of food and oxygen) photosynthesis and metabolism.
- Plants were sent to ISS in the Biomass Production System (BPS) and grown for several generations. Plants grown on ISS were compared to plants that remained on Earth in a BPS.
- The ability to grow food while in space will greatly increase the success of future long duration missions to the Moon and Mars.
The PESTO investigation, conducted in concert with technology verification for the BPS hardware, measured the canopy photosynthesis (the production of oxygen and carbohydrates from carbon dioxide and water in the environment) of Triticum aestivum (super dwarf wheat). The wheat was grown under high light and controlled carbon dioxide conditions in microgravity. The investigation also measured the metabolic effects on the photosynthetic apparatus to quantify the effects on metabolism and to model the impact of microgravity on biological approaches to atmospheric regeneration.
To test the hypothesis that the carbon exchange rates would be the same in microgravity as on Earth, investigators measured and characterized the carbon dioxide and light response curves for a wheat photosynthetic canopy grown in microgravity. Data came from various sources: gas samples taken from the closed atmosphere inside the chambers; liquid samples taken through ports in the chambers; plant tissue samples extracted by the crew during different points in the growth cycle; and, finally, plant tissue extracted from the live plants returned to Earth inside the BPS. The investigators analyzed the plant tissue postflight for primary photosynthesis parameters, such as electron transport, carbohydrate partitioning, and photosystem (the biochemical pathway for photosynthesis). Measurements were taken over a range of relative humidity conditions to discover whether atmospheric vapor pressure deficits affect gas exchange in microgravity.
The amount of food necessary to sustain a crew during a long-duration mission to Mars would prohibitively increase the mass of spacecraft and the overall cost of the mission. A possibility to alleviate this problem could be the use of plant systems as food sources or for regenerative life support systems. The biomass production systems may also be used as a filtration system for water and atmospheric gases.
As less fertile land becomes available to grow food, alternative agricultural systems that efficiently produce greater quantities of high-quality crops will be increasingly important. Data from the operation of the BPS will advance greenhouse and controlled-environment agricultural systems and will help farmers produce better, healthier crops in a small space using the optimum amount of nutrients.
BPS consisted of four plant growth chambers. PESTO operations grew Triticum aestivum in three of the four BPS chambers. Each chamber has 264 cm square growth area, while the roots of the plant were placed 3 cm below the growth area. A total of 32 plants were grown for 73 days on ISS. The plants were exposed to 20 hours of light and 4 hours of dark daily at 24 degrees C and 78 percent relative humidity. A control group of plants on Earth, were treated exactly as the experimental group on ISS. Although BPS is fully automated, the crew conducted periodic system checks and some support tasks for PESTO.
Following the transfer of the BPS to EXPRESS Rack 4, the crew refilled the water reservoirs as needed and periodically changed carbon dioxide canisters. Gas and liquid samples using ports in the growth chambers were taken weekly. Plant samples were taken for harvesting and fixation 21 days following BPS activation on ISS. The fixed samples were stowed in ARCTIC. The crew used the harvested plants to hand-pollinate blooms on other plants and harvested seeds. BPS was returned to Earth on Shuttle flight 8A while the plants continued to grow.
Data and near realtime video from inside the growth chambers were transmitted from BPS to the investigators via the Telescience Resource Kit (TReK) system. Student and teacher participants in the ISS Challenge: Farming in Space program were able to view the realtime video from BPS. The participants conducted their own in-class plant-growth experiments and were encouraged to share questions and data with other participants and members of the ISS Challenge support team.
During ISS Expedition 4, PESTO grew 32 plants for 73 days inside the plant growth chambers of the Biomass Production System (BPS). Following return to Earth, these plants were compared to ground controls that were grown in BPS plant growth chambers on Earth.
The PESTO investigation had three dimensions that resulted in a more complete picture of microgravity influences on photosynthesis: gas exchange, partitioning and metabolism. Carbon dioxide and light response curves allowed researchers to establish whether canopy photosynthetic responses were affected by space conditions. This is noteworthy since plants can be used to regenerate the atmosphere in space conditions though removal of carbon dioxide and production of oxygen. In addition, the tests that evaluated movement of water via transpiration are important since they are indicative of the stomatal responses that regulate photosynthesis. Further, the impact of microgravity on transpiration was significant since plants can be used to purify water under space flight conditions. These studies involving gas exchange at elevated carbon dioxide concentrations increased our understanding of the biological impacts of increasing levels of atmospheric carbon dioxide on Earth-based ecosystems. Furthermore, an understanding of plant responses under a range of carbon dioxide and light conditions has potential benefits to commercial, controlled environment, agriculture industries.
The growth and development of the dwarf wheat plants on the ISS was similar to the growth and development of plants on Earth. Analysis of the plants indicated that the microgravity-grown plants were 10% taller than plants grown on Earth, although the growth rate of dwarf wheat leaves was very similar to the plants grown on Earth. The near-real-time video data provided by BPS allowed for validation of the growth data in microgravity when compared to the controls. Design applications can be made to the BPS to allow for successful plant production on the ISS and future long-duration missions to the Moon and Mars (Stutte et al. 2003).
To effectively farm in space, multiple redundant plant growth chambers will be needed to acquire the maximum yield of food, oxygen, and water. PESTO evaluated the transpiration (water) and photosynthesis (oxygen) processes of the dwarf wheat plant in microgravity and found that microgravity did not affect either the transpiration or the photosynthesis processes of the plants (Monje et al. 2005).
When environmental controls such as temperature, relative humidity, carbon dioxide, and water are effectively maintained, microgravity does not affect canopy growth of dwarf wheat plants. Slight differences in photosystem I (photosynthesis in which light of up to 700 nm is absorbed and reduced to create energy) and photosystem II (photosynthesis in which light of up to 680 nm is absorbed and its energy is used to split water molecules, giving rise to oxygen) were noted and are being evaluated further (Stutte et al. 2005).
When conducting biological studies, it is important to maintain the integrity of the samples. The standard method to preserve samples is quick freezing at low temperatures (-80 degrees C (-112 degrees F) and below), but strict temperature control of samples on station is not always uniform or possible. Therefore, a preservative is needed that will maintain the integrity of biological samples before cooling. RNAlaterTM was used to preserve some of the PESTO samples on station. The viability of the samples preserved with RNAlaterTM was greater than that of the samples preserved using formalin. To carry out long-term studies aboard ISS, a fixative such as RNAlaterTM is needed to maintain the integrity of samples at the varying temperatures that are experienced on ISS (Paul et al. 2005).
The objective of PESTO was to determine what effects microgravity have on chloroplast development, carbohydrate metabolism, and gene expression in the leaves of the plants grown on the ISS. PESTO data indicated that microgravity alters leaf development, cell structure and chloroplast morphology, but does not compromise the overall physical function of the plant (Stutte et al. 2006).
Stutte GW, Monje O, Hatfield RD, Paul A, Ferl RJ, Simone CG. Microgravity effects on leaf morphology, cell structure, carbon metabolism and mRNA expression of dwarf wheat. Planta. 2006; 224(5): 1038-1049.
Monje O, Stutte GW, Chapman DK. Microgravity does not alter plant stand gas exchange of wheat at moderate light levels and saturating CO2 concentration. Planta. 2005; 222(2): 336-345. DOI: 10.1007/s00425-005-1529-1.
Stutte GW, Monje O, Anderson S. Wheat (Triticum Aesativum L. cv. USU Apogee) Growth Onboard the International Space Station (ISS): Germination and Early Development. Plant Growth Regulation Society of America, Miami Beach, FL; 2003 64-69.
Frazier CM, Simpson JB, Roberts MS, Stutte GW, Fields ND, Melendez-Andrade J, Morrow RC. Bacterial and fungal communities in BPS chambers and root modules. SAE Technical Paper. 2003; 2003-01-2528. DOI: 10.4271/2003-01-2528.
Stutte GW, Monje O, Goins GD, Tripathy BC. Microgravity effects on thylakoid, single leaf, and whole canopy photosynthesis on dwarf wheat. Planta. 2005: 1-11. DOI: 10.1007/s00425-005-0066-2.
Stutte GW, Monje O, Porterfield DM, Goins GD, Bingham GE. Farming in Space: Environmental and Biochemical Concerns. Advances in Space Research. 2003; 31: 151-167.
Ground Based Results Publications
Liao J, Liu G, Monje O, Stutte GW, Porterfield DM. Induction of hypoxic root metabolism results from physical limitations in O2 bioavailability in microgravity. Advances in Space Research. 2004; 34: 1579-1584.
Stutte GW, Monje O, Goins GD, Chapman DK. Measurement of Gas Exchnage Characteristics of Developing Wheat in the Biomass Production System. SAE Technical Paper. 2000; 2000-01-2292. DOI: 10.4271/2000-01-2292.
Morrow RC, Stadler JJ. Analysis of Crew Interaction with Long-Duration Plant Growth Experiment. SAE Technical Paper. 2003; 2003-01-2482. DOI: 4271/2003-01-2482.
Stutte GW, Monje O, Goins GD, Ruffe LM. Evapotranspiration and Photosynthesis Characteristics of Two Wheat Cultivars Measured in the Biomass Production System. SAE Technical Paper. 2001; 2001-012180. DOI: 10.4271/2001-01-2180.
Farming in Space
NASA Image: ISS004E10128 - Close-up view of Apogee Wheat Plants grown as part of the PESTO investigation during ISS Expedition 4.
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Video screen shot of Triticum aestivum 20 days after planting inside the BPS, on ISS during Expedition 4. Image courtesy of Space Daily.
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NASA Image: ISS004E10138 - Close-up view of Apogee Wheat Plants with a scale as backdrop to exhibit the growth of the plants grown as part of the PESTO on ISS Expedition 4.
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