Editor’s note: Prof. Dayanandan is a Botanist by profession and has been a student, teacher and researcher at the Madras Christian College and the University of Michigan. He has inspired students for more than 40 years. Prof. Dayanandan is passionate about communicating Science to school students and general public and believes that even the most sophisticated concepts in Science can and should be shared with non-specialists. Recently, he was an invited speaker at Chennai Freethinkers’ Thinkfest 2011, where he delivered a lecture ‘Chimpanzee is our cousin. So is the Neem Tree.’ His other research interests include Evolutionary Biology, Art History and Tamil literature.
‘Space travel’ holds much fascination. If sending human beings to Mars has to come true what would we need in terms of catering to the nutritional requirements of the astronauts? What kinds of experiments are conducted at the International Space Station that keeps orbiting the earth? Does Space research have a tangible benefit for people on earth? Space Biology is an interesting topic and this FAQ seeks to whet your appetite on some of these issues.
This FAQ is summarized from a Mini Review that appeared in the December 2011 issue of Journal of Biosciences, a quarterly journal published by the Indian Academy of Sciences, Bangalore.
1) What is Gravitational and Space Biology?
Life evolved during the past four billion years under the influence of the Earth’s massive field of gravity. Several features of life were shaped by gravity as organisms adapted to living in water, air, land and on trees. Gravitational Biology explores how organisms perceive and respond to gravity and how gravity influences the structure, development, function, evolution and behavior of organisms (Morey-Holton 2003). Space Biology is often used as an all-encompassing term to describe the functioning of life processes in normal and altered gravity conditions on Earth and in space.
2) How does gravity influence life?
Of the four fundamental forces only electromagnetism is directly involved in biological processes. No direct role is known either for the strong or weak nuclear forces or gravity in any biochemical process. Gravity influences living organisms indirectly. Gravitational force is infinite-range acting, and positively acts on all particles with mass/energy. Any object with a mass at the surface of the Earth accelerates towards Earth’s center at approximately 9.81 m/s2. This acceleration due to gravity at the Earth’s surface is generally treated as 1 g (one Earth Gravity). The dilemma of growing in 1 g environment and responding to it can be seen in nearly 400 million-year-old fossil vascular plants and their descendants.
4) What is Microgravity?
Microgravity refers to considerably less than 1 g force, usually in the range of 10-4 to 10-6 g. Microgravity in this range can be provided for short duration by generating free fall conditions close to the Earth’s surface with sounding rockets and airplanes in parabolic flight and drop facilities (Clement and Slenzka 2006). Space vehicles are unique biological laboratories. Space Biology experiments are generally carried out in Low Earth Orbits (LEO), at altitudes less than 1% of the distance from the Earth to Moon. Space vehicles moving in circular LEO experience actual microgravity environment because of free fall around the Earth. The centripetal force towards the Earth is counterbalanced by the centrifugal acceleration resulting in free fall.
5) What are the observations regarding the effect of microgravity on plant growth?
Microgravity affects normal plant growth by interfering with the supply of water, minerals and oxygen and removal of carbon dioxide from the root zone. These problems are now overcome by development of appropriate delivery systems (Wolverton and Kiss 2009). Ethylene gas functions as a natural plant hormone at low concentrations. Ethylene build-up inside the space vehicle was found to be the major cause of reproductive failure in microgravity. When ethylene concentration is controlled, wheat, peas and Arabidopsis plants could be successfully cultivated to produce viable seeds in space. Potato leaf and stem cuttings were cultured in Astroculture facility and mini-tubers were harvested. The tuber size, morphology and starch granules were all similar to ground controls.
It appears that microgravity does not adversely affect genetically determined developmental processes and that as long as the environment of the cabin is controlled, growth and development of plants might proceed normally without affecting important processes such as gas exchange, photosynthesis and reproduction. The growth of four consecutive generations of peas in space has given the confidence that food plants can indeed be grown for space travel and colonization. Unusual and unexpected responses too were observed. A miniature rose that bloomed in microgravity in the Astroculture growth chamber on a shuttle produced unique essential oils and rose-fragrance that was subsequently commercialized.
6) Does gravity have an effect on animals too?
In the animal kingdom response to gravity has been studied in all major groups. Organs such as the Johnston’s organ in insects and the vestibular apparatus of higher animals detect gravity for proper orientation. The musculo-skeletal system evolved to support the body mass and provide structural and postural stability to land animals as they moved about in search of food. The sensory-motor system evolved so that organisms can recognize the gravity vector and orient themselves and move about. A vestibular system evolved in the fish for efficient swimming. The versatile design of this system, with minor modification in nerve-motor connections, was retained by amphibians, reptiles, birds and mammals for navigation in water, air, trees and land. Human beings have inherited many of these evolutionary adaptations (Highstein et al 2004). The vestibular system is the key to human senses of balance, motion, and body position. The otolith organs allow humans to sense the direction and speed of linear acceleration and the position (tilt) of the head. The semicircular canals help sense the direction and speed of angular acceleration (Coulter and Vogt 2004).
As a bipedal erect animal the genus Homo had to adapt to gravity for at least 2.4 million years. Their ancestral bipedal hominins faced this dilemma nearly 7 million years ago. The cardiovascular system helped maintain adequate pressure and supply of blood to various parts of the body, especially the head.
7) How have animals fared in space? What is the effect of microgravity on animals?
The Space Age dawned in 1957 when Sputnik I was launched into successful orbit around the Earth. This was followed by space flights of Gagarin and Shepherd in 1961 and Glenn in 1962. The history of animals in space, however, is more than 229-years-old! In 1783 a French team sent a rooster, duck and sheep on a hot air balloon and successfully recovered them. Tipton (2003) described the history of animals in space under three eras – the balloon, rocket-missile and biosatellite. Now, we are in the era of Space Station and Nanosatellites which continue experiments with animals as well as with plants, bacteria, yeasts and organic chemicals.
About 40 different animal species have so far been flown in space. Invertebrates such as jellyfish, sea urchins and pond snails have been used to study fertilization and development of graviperceptors. C. elegans can reproduce and progress through several generations in microgravity without major structural changes. Recent studies on C. elegans offer hope for treatment and control of muscle degradation (Etheridge et al 2011).
Currently fish, birds, amphibians and small mammals are the favorite organisms for developmental studies in microgravity. Medaka (Oryzias latipes) and swordtail fish (Xiphophorus helleri) were studied onboard the Spacelab for embryogenesis and otolith development. In microgravity fish exhibit a peculiar looping behavior. Successful mating of Medaka in microgravity was first observed in 1994. Viable embryos resulted and the fry had no abnormalities. Normally, the fertilized eggs of frogs rotate before further development. In reduced gravity frogs were found to ovulate but the fertilized eggs did not rotate. Yet the tadpoles emerged and appeared normal, and when returned to Earth metamorphosed and developed normally (Morey-Holton 2003).
The Japanese quail (Coturnix coturnix) is another favorite space animal and a potential source of food for future space colonies. On Mir fertilized quail eggs developed normally but the hatchlings had trouble orienting. A chick would spin and tumble unless held in hands by an astronaut. In young rats bone loss, accompanying muscle loss and delay in bone fracture repair are serious adverse effects of microgravity. Such studies have helped develop countermeasures for long term human occupation of space vehicles (Morey-Holton et al 2007).
8 ) What is the effect of hypergravity and microgravity on human beings?
Human beings can tolerate only 4 to 5 g for up to 10 min. During launch and reentry humans normally experience 3 g conditions. Hypergravity above 50 g even for a few seconds causes serious injury or death. In an orbiting space vehicle microgravity field is typically in the range of 10-4 to 10-6 g. This has a deconditioning effect leading to abnormal physiological changes (Clement 2003; Davis et al 2008). Calcium depletion can lead to up to 1-2% loss in bone density per month. Muscle fiber loss can lead to up to 40% reduction in muscle function. In addition space radiation, sensory deprivation and absence of circadian clues and the artificial environment all have adverse effects on human beings. While most conditions disappear on return to Earth some such as bone calcium loss take a long time to or never recover. That humans can indeed stay for extended periods in microgravity is shown by the fact that Mir was home for 125 astronauts from more than a dozen countries while 196 astronauts from 8 different countries have visited the ISS from 2000 to 2010. Cosmonaut Valeri Polyakov has stayed in Mir for 437 days.
NASA currently addresses human health and safety issues through its Human Research Program. Prospects of return to lunar surface and long-term space missions require that in addition to safety and countermeasures advanced technologies, diagnostic devices and remote-controlled protocols should be developed for astronauts themselves to solve problems, respond to emergencies and self-administer medical care.
9) What are the key findings with regard to microbes and cells?
A recent study has established that the small size of microbes help them withstand extreme hypergravity conditions (Deguchi et al 2011). Young plants can tolerate only about 10 min exposure to 40 g while 20 g can be lethal for rats. Four species of bacteria and the yeast Saccharomyces cerevisiae could proliferate even at 20,000 g. Paracoccus denitrificans and E. coli survived and even proliferated at 400,000 g. A major conclusion from recent experiments with cell culture on bioreactors such as CBOSS on ISS is that many cell types – human blood, kidney, liver, tonsil, immune system tissue, and colon cancer cells – can be cultivated in microgravity and that such cells have normal form and function as cells and tissues in ground controls.
10) What is Astrobiology?
Astrobiology is the study of life in the universe. Astrobiology deals with such questions as origin and evolution of life on Earth, possible existence of life elsewhere in Universe, future of life, and living on celestial bodies other than the Earth. Many questions can be raised: Are the low levels of gravity force on the Moon (1/6 g) and Mars (3/8 g) sufficient for providing threshold levels for normal functioning of plants, animals and humans? Can life continue to evolve in such low gravity fields and return to Earth and successfully adapt to Earth’s 1 g environment? Mars poses many challenges for humans: a hostile and lethal atmosphere, ionizing radiation, low gravity and light and prolonged isolation from familiar community, lifestyle and biodiversity. The most challenging of all problems of colonizing any extraterrestrial body is providing a permanent life support system. An ambitious theoretical proposal is to terraform a planet by converting the surface and climate to make them suitable for life (Davies et al 2003; Fogg 1995).
11) What are Bioregenerative Systems?
Space travel and space colonization require a life support system that mimics the environmental conditions, including the supply of food that humans and other living things are used to. A complete life support system is variously known as Bioregenerative System (BRS), Advanced Life Support System (ALSS) etc. A BRS is based on the fundamental principles of biospherics, namely, imitating the ecological and environmental elements that make life self-sustaining in the Earth’s biosphere (Eckart 2010). The three major components of a bioregenerative life support system are: plants, people and microbes. Plants produce biomass including edible food, release oxygen during photosynthesis and transpire water that can be condensed and collected. People consume food and use oxygen but release carbon dioxide and water and solid waste as urine and feces. People also use water for washing and bathing and this is termed as ‘gray water.’ The human waste, inedible biomass from plant and the gray water can all be used in a microbial bioreactor for recycling into nutrients and carbon dioxide.
Current research is also focused on how plants respond to hypobaria, or low pressure. Atmospheric pressure on Lunar and Martian surface is less than one per cent of what it is on Earth. Plants interpret low pressure as conditions of aridity and activate drought sensing genes even if water is plentiful and humidity is high. This may lead to closure of stomata, poor photosynthesis and leaf shedding. The thin atmosphere, space radiation and particle bombardment will seriously affect human and plant health on Mars. It has been suggested that first human and agricultural settlements could be underground or in natural Martian caves such as those around Arsia Mons. Light may be piped down from solar collectors, and plants grown initially hydroponically (Salisbury et al 2002). Carbon dioxide is not a constraint since the Martian atmosphere consists of 95% of this gas. Recently Chandrayaan-1 spacecraft detected a large cave on the Moon which has been suggested as a potential place for a future lunar outpost.
12) What is Space farming?
Growing plants in space in BRS is popularly described as Space Farming. ‘Space Crop Plants’ should be: nutritious, highly efficient in utilizing low light, compact in growth habit, resistant to microbial diseases and have high harvest index (NASA Science 2001). Such plants, already cultivated in space vehicles include: rice, wheat, and salad leafy greens and vegetables such as lettuce, spinach, peppers, mustards, tomatoes, onions, Swiss chard, broccoli, radishes, potatoes, sweet potatoes, peanuts, soybean, cowpea and strawberries. Super-dwarf cultivars of wheat (Apogee and Perigee) and rice have been developed, and Apogee wheat has already been grown from seed to seed in microgravity. Ornamental plants such as tulips are considered to be ideal for aesthetic and positive psychological ambience.
When India takes up space biological studies it will find that common greens such as species of Amaranthus and Alternanthera sessilis and Mentha spicata qualify as ideal space plants. It is estimated that a five-year mission to Mars would require about 3,125 kg foods per astronaut. This could be met if food is produced in space in BRS and the astronauts themselves process and cook some of their meals. Plants such as lettuce, cabbage, spinach, carrots, tomatoes, spring onions, radishes, peppers, strawberries and some herbs could be cultivated in space. Some harvested food can also be processed and sent in advance in unmanned spacecrafts to Mars.
13) What are the applications of Space Biology?
Space biology has potential applications in medicine, biotechnology, molecular synthesis, crop improvement, alternate agricultural systems, nutrition and food preservation and improving environmental quality and sustainability of life. Technological development can lead to space product development and technology transfer benefiting society (Hertzfeld 2002). Research in space biology may provide solutions to common problems such as shrinking productive land, low crop yield, pollution and vector-borne diseases. Gravitational and space biology is a multidisciplinary field drawing expertise and inspiration from such diverse fields as astronomy, physics, biology, medicine, material sciences, nanotechnology, agri-horticulture, and information technology. It has the potential to ignite young minds, even school students, thus promoting interest in science and scientific temper.
14) What is the scope for the study of Space Biology in India?
India has a presence in Space Science and Technology but not in Space Life Sciences. Gravitational biology and Space Life Sciences are not taught in any Indian university. ISRO’s Space biological studies are limited to a balloon based experiment carried out in 2001 and repeated in 2005, and the forthcoming Space Capsule Recovery Experiment (SRE-II). The balloon experiment collected samples from the stratosphere between 20-41 km. Twelve bacterial and six fungal colonies were recovered which included three new species of bacteria. The SRE-II will carry out three different biological experiments in microgravity. ISRO’s ‘Space Vision India 2025’ statement includes Planetary Exploration and Human Space Flight Programme. An ISRO Orbital Vehicle might carry a 2-3 member crew to a LEO before 2020.
With clear mandate and adequate funding, research can be initiated in universities and especially in ISRO and its units such as Space Application Centre, Indian Institute of Space Science and Technology, the proposed astronaut training centre and through Vikram Sarabhai Space Centre’s RESPOND program. Government agencies should encourage and fund research and popularize Space Life Sciences. Students’ initiatives in Space Sciences are now encouraged in academic institutions such as the SRM University and Vellore Institute of Technology in Tamilnadu. These and other institutions should be encouraged and supported to pursue research in Space Biology.