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).
