Life and Gravity

Abstract

All organisms on earth have evolved at unit gravity and thus are probably adapted to function optimally at 1 g. However, with the advent of space exploration, it has been shown that organisms are capable of surviving at much less than 1 g, as well as at greater than 1 g. Organisms subjected to increased g levels exhibit alterations in physiological processes that compensate for novel environmental stresses, such as increased weight and density-driven sedimentation. Weight drives many chemical, biological, and ecological processes on earth. Altering weight changes these processes. The most important physiological changes caused by microgravity include bone demineralization, skeletal muscle atrophy, vestibular problems causing space motion sickness, cardiovascular deconditioning, etc. Manned missions into space and significant concerns in developmental and evolutionary biology in zero and low gravity conditions demand a concentrated research effort in space-medicine, physiology and on a larger scale -gravitational biophysics. Space exploration is a new frontier with long-term missions to the moon and Mars not far away. Research in these areas would also provide us with fascinating insights into how gravity has shaped our evolution on this planet and how it still governs some of the basic life processes. Understanding the physiological changes caused by long-duration microgravity remains a daunting challenge. The present concise review deals with the effects of altered gravity on the biological processes at the cellular, organic and systemic level which will be helpful for the researchers aspiring to venture in this area. The effects observed in plants and animals are presented under the classifications such as cells, plants, invertebrates, vertebrates and humans. . Downloaded from www.worldscientific.com by UNIVERSITY OF AUCKLAND LIBRARY -SERIALS UNIT on 03/15/15. For personal use only.300 S. Bhaskaran, S. S. Jagtap & P. B. Vidyasagaralso adapted to utilize it for their benefit. For instance, large marine creatures like whales use their capacious lungs as buoyancy tanks and use their fins and tails to remain afloat or to be mobile. Without these adaptations, they would have quickly sunk to the seabed. Protozoa seem to utilize gravity depending on the preferred living conditions. 1 Paramecium which feeds on aerobic bacteria, shows a negative gravitaxis, i.e. the cell population swims mainly upwards, against the gravity vector, thus reaching oxygen saturated layers. Some species such as aquatic insects detect gravity using air bubbles trapped in certain passageways viz., tracheal tubes. 2 However, most organisms use statocysts consisting of a fluid-filled chamber lined with a hairy, touch-sensitive epithelium containing statolith which is a solid granule of higher density. 2 Interestingly, biological systems have been able to exploit their designs and molecular mechanisms to increase the sensitivity of their thresholds of detection. The vibrations detected by the Corti organ in a mammalian inner ear can be of the sam...

Effects of Short-term Hypergravity Exposure on Germination, Growth and Photosynthesis of Triticum aestivum L.

“…Among them, centrifuge systems have been widely used to analyze the effect of hypergravity perception and response in plants. Exposures to hypergravity values have been shown to affect growth, development and cell wall properties in various plants (Waldron and Brett 1990;Hoson et al 1996;Soga et al 1999a, b;Tamaoki et al 2006;Nakabayashi et al 2006;Bhaskaran et al 2009). In most of the earlier reports, three to five days old seedlings were exposed to higher g values up to 300 g for longer durations and effects were studied.…”

Gravitaxis in Euglena

“…Besides a pure vectorial addition or subtraction some species can even actively accelerate during upward swimming and decelerate during downward swimming, thereby at least partially compensate passive sedimentation (Häder et al 2005a), a phenomenon which is called gravikinesis (Machemer et al 1991;Machemer and Machemer-Röhnisch 1996;Gebauer et al 1999;Bhaskaran et al 2009) and is found in many ciliates such as Paramecium, Loxodes, Didinium and Stylonychia (Krause et al 2010) and is controversially discussed in Euglena (Machemer-Röhnisch et al 1999;Häder et al 2005a). …”

Aspectos reprodutivos de orquídeas em ambientes de Vereda do Cerrado

“…Thus, life forms are not only shaped by this important physical force but adapted to use it for their own benefit (Morey-Holton, 2003;Bhaskaran et al 2009). Plants respond to gravity in different levels that range since intracellular mechanisms until growth and development, in a way that arranges their spatial orientation and survival (Bhaskaran et al 2009). In this study, we show that gravity influences flower resupination in two different but complementary ways: gravitropism and gravitation.…”

“…The direction and intensity of gravity have been constant throughout the evolutionary history of life on Earth, acting on all organisms. Thus, life forms are not only shaped by this important physical force but adapted to use it for their own benefit (Morey-Holton, 2003;Bhaskaran et al 2009). Plants respond to gravity in different levels that range since intracellular mechanisms until growth and development, in a way that arranges their spatial orientation and survival (Bhaskaran et al 2009).…”