WHY GROW PLANTS IN SPACE ?
by Bonnie McClain and Tom Scott
There is abundant evidence that microgravity affects virtually every aspect of plant growth. Space flight provides the only known environment in which fundamental biological processes and mechanisms can be studied in the absence of the sometimes overriding effects of gravity. Removing gravity for long periods of time allows new perspectives in the study of plants.
Answers to important questions about the basics of plant growth and development lie in understanding the role gravity has on plant processes and responses of plants to their environment. For example, gravitropism is the bending response of plants to the force of gravity with the roots growing downward and the shoots growing upward. Charles Darwin began experiments on plant gravitropism during the last century. Yet, the mechanisms of this process are still not clear. The more knowledge we generate about these basic processes of how plants function, the more likely it is that we can adapt that information into practical, useful new applications and products enhancing our daily life on Earth.
NASA's research with plants in space is dedicated to systematic studies that explore the role gravity plays at all stages in the life of higher plants. Research includes scientific questions focused on determining effects of interactions of gravity and other environmental factors on plant systems, and on using hypergravity, simulated hypogravity, and microgravity as tools to advance fundamental knowledge of plant biology. Plant research results contribute to NASA's goals of furthering human exploration of space and improving the quality of life on Earth through applications in medicine, agriculture, biotechnology, and environmental management.
Plant science research questions focus on five objectives: 1) to explain basic mechanisms whereby plants perceive, transduce, and respond to gravitational force (examples: comparisons of seedling vs. older plant responses to gravity); 2) to understand the role of gravity and microgravity in developmental and reproductive processes in plants (examples: flower development and wood formation); 3) to learn how metabolic and transport processes are affected by gravity and microgravity (examples: photosynthesis and long and short distance sugar transport); 4) to analyze interactions of microgravity with other important parameters of space (examples: cosmic radiation and electromagnetism); and 5) to study the role of plants within recycling life support systems for space exploration (examples: carbon dioxide production and oxygen revitalization).
Knowledge of physiology, cell biology, biochemistry, and molecular biology of plants coupled with biotechnology advances contribute to our fundamental knowledge of plants and provide impetus for a new era of plant investigations. The opportunity to experiment at a micro level of gravity 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 it 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, and the interaction with other signals assumes such significance for plant science. These investigations could allow us to unravel the precise control mechanisms involved in dictating plant form, structure, and function. 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 reaction 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 would be the ability to control plant form, and forestry would benefit with faster methods of regeneration of lost forest areas.
Before the first lunar outpost, the proposed Mars base, and other future missions from planet Earth can become realities, numerous scientific and technological problems remain to be solved. None of these problems is more important than that of supporting human life in space. Long-duration human exploration missions will require life support capabilities beyond those now available. A solution is to develop technologies that integrate physical and chemical processes into a dynamic, recycling life support system. Plants and humans will provide the interdependent biological processes of a life support system. Studying plants in space will acquire the scientific information necessary for development of such a system. Plants will be a primary component of atmospheric regeneration; carbon dioxide exhaled by humans will be taken up by plants and used in photosynthesis, returning oxygen and food to the crew. Plants are also important to water regeneration. The productivity of plants relative to the input of energy (light) can be increased by using such techniques as carbon dioxide enrichment and hydroponics. To achieve a controlled life support system, ground-based research in growth chamber facilities will be conducted as well as plant investigations in the microgravity environment of space flight.
Why study plants in space? The discoveries made, lessons learned, and technologies developed from these investigations will benefit those of us on planet Earth as we unlock and utilize gravity's mysteries to enhance our journey beyond Earth's boundaries.