Research Questions

Can plants survive and thrive in space? Can they grow, develop, reproduce, and orient themselves normally in the virtual absence of gravity. Will the space environment affect their metabolism and photosynthesis, which are so dependent on the 12-hour cycling of day and night? How will space affect seed viability and seed germination? A number of factors such as pollen viability, aspects of fertilization, and floral development influence reproduction. These are important aspects for space horticulture (Table 1-06).

Knowledge of physiology, cell biology, biochemistry and molecular biology of plants coupled with biotechnology advances contributes to our fundamental knowledge of plants and provides impetus for a new era of plant investigations. The opportunity to experiment in microgravity provides a new dimension that enables interdisciplinary plant research to answer important questions about the plant's reception of the gravity signal, the plant's biochemical interpretation of that signal, and how that interpretation causes a developmental reaction. It appears that this reaction system, in general, interacts with receptor systems that detect both internal and external signals. It is for this reason that understanding the role of mechanical signals, such as gravity, assumes such significance for plant science: these investigations could begin to reveal the precise control mechanisms involved in dictating plant form, structure, and function.

Figure 1-20. A close-up view of water droplets on leaves on a Russian plant growth experiment on board the International Space Station. Photo courtesy of NASA.

Figure 1-20. A close-up view of water droplets on leaves on a Russian plant growth experiment on board the International Space Station. Photo courtesy of NASA.

Understanding how basic processes can be manipulated and put into use in new ways that develop new products and increase productivity is the basis for biotechnological applications in agriculture, horticulture, and forestry. For example, understanding the interaction between gravity and light could be the basis for genetic engineering of plants resulting in increased crop productivity while minimizing the required growing space. Application to horticulture could include the ability to control plant form, and forestry could benefit from faster methods of regeneration of lost forest areas (McClain and Scott 1997).

Years of research in space have demonstrated that plants, as well as humans and animals, are affected by spaceflight. Researchers have found that changes detected by plant gravity sensors result in alterations of growth patterns, biomass production, and development in plants during spaceflight. Cell division is decreased in space-grown plants and chromosomal abnormalities such as breakage and fusion are reported to occur more frequently in plants grown in space than in those grown on Earth.

Understanding these changes is critical because the Closed Ecological Life Support Systems (CELSS) needed to support humans during future long-term space travel depend on the ability to grow plants reliably and efficiently in space. Regular resupply of air and food constitutes a major cost of operating a space station. So, in plant research, applied questions result from the need to maximize food production while minimizing the required onboard spatial volume or from the need to raise plants in an entirely closed environment.

Obviously, the use of plants as food in space requires that the effects of gravity on the morphology of the organism to be known. This requirement must be placed upon all plants considered as food sources for CELSS. It

Current

Gravity perception

Morphology/structure

Development/genetics

Growth

Future

Cell/tissue competence, differentiation

Developmental timing

Organ development

Cellular function

Metabolism/metabolites

Photosynthesis, respiration

Fluid dynamics, transport

Interaction of gravity with light, radiation, other forces

Table 1-06. Current andfuture space research Plant Biology.

Table 1-06. Current andfuture space research Plant Biology.

involves investigation of gravity effects during all of the developmental phases of the plants, from germination to maturation and fruiting. Also, studies are required to assure that culture and harvesting techniques appropriate on Earth will be applicable in space. Finally, experiments should assure that the nutritional composition (and the taste) of the organisms does not differ appreciably from that found on Earth.

The Earth is continuously bathed in high-energy ionizing radiation known as Galactic Cosmic Radiation (GCR), emanating from outside the solar system, and sporadically exposed to bursts of energetic particles from the Sun referred to as Solar Particle Events (SPEs). The main source of GCR is believed to be supernovae (exploding stars), while occasionally a disturbance in the Sun's atmosphere (solar flare or coronal mass ejection) leads to a surge of radiation particles with sufficient energy to penetrate the Earth's magnetic field and enter the atmosphere (Figure 1-21).

Outside the Earth's atmosphere, GCR consists mostly of fast-moving protons (hydrogen nuclei) and alpha particles (helium particles). GCR is 98% atomic nuclei and 2% electrons. Of the energetic nuclei, 87% are protons, 12% are helium ions and 1% is heavier ions. So, GCR, along with other forms of radiation presents a problem for space biology. In terms of biological development, space radiation is a major factor that must be understood in order for humanity to move deeper into space.

Ionizing radiation refers to subatomic particles that, on interacting with an atom, can directly or indirectly cause the atom to lose an electron or

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