Spaceflight Exposure Effects on Transcription, Activity, and Localization of Alcohol Dehydrogenase in the Roots of Arabidopsis thaliana

Abstract

Although considerable research and speculation have been directed toward understanding a plant's perception of gravity and the resulting gravitropic responses, little is known about the role of gravity-dependent physical processes in normal physiological function. These studies were conducted to determine whether the roots of plants exposed to spaceflight conditions may be experiencing hypoxia. Arabidopsis fhaliana (1.) Heynh. plants were grown in agar medium during 6 The increase in ADH activity associated with the spaceflight roots was realized by a 28% decrease in oxygen availability in a groundbased study; however, no reduction in redox potential was observed in measurements of the spaceflight bulk agar. Spaceflight exposure appears to effect a hypoxic response in the roots of agar-grown plants that may be caused by changes in gravity-mediated fluid and/or gas behavior.

Transgene Expression Patterns Indicate That Spaceflight Affects Stress Signal Perception and Transduction in Arabidopsis

“…One stressful feature of spaceflight that may reflect this type of synergism is the apparent hypoxia-like effects that have been observed in orbital plant experiments. Plants demonstrate increased aerenchyma formation and an increase in ADH mRNA and enzyme activity, all symptoms consistent with root zone hypoxia (Musgrave et al, 1997;Porterfield et al, 1997b). In these cases, the plants were grown such that the roots were encased within an agar growth medium and the ground controls exhibited elevated levels of Adh mRNA and enzyme activity, as well.…”

“…It is generally agreed that a spaceflight environment influences plant physiology (Tripathy et al, 1996;Hampp et al, 1997;Merkys and Darginaviciene, 1997;Perbal et al, 1997;Porterfield et al, 1997b;Kiss et al, 1999;Driss-Ecole et al, 2000). However, the causes of these influences are not easily understood, and it is difficult to dissect the intrinsic biological effects of microgravity or spaceflight away from the secondary and synergistic effects generated by the systems designed for life support.…”

“…ADH is a crucial enzyme for plant fermentative metabolism, which functions in the regeneration of the NADϩ needed to sustain glycolysis and maintain basal production of ATP when the cytochrome chain is arrested under oxygen-limiting conditions (Crawford, 1982;Jackson and Drew, 1984;Daugherty et al, 1994;Vartapetian and Jackson, 1997). Initial analyses of plants grown in spaceflight revealed elevated levels of ADH activity and Adh mRNA compared with ground-control plants (Porterfield et al, 1997a(Porterfield et al, , 1997b. These observations suggest that hypoxic stress, perhaps caused by the lack of convective gas exchange in microgravity, may play a major role in the effects of spaceflight on plant growth and development.…”

“…At the cellular level, spaceflight has been associated with disruptions of microtubular self-organization (Papaseit et al, 2000), changes in amyloplast distribution (Perbal et al, 1997;Kiss et al, 1999;DrissEcole et al, 2000) and energy metabolism (Hampp et al, 1997), and alterations in the distribution and partitioning of calcium ions (Merkys and Darginaviciene, 1997). At the organismal level, plants have responded to spaceflight with variations in basic physiological processes such as electron transport rates in photosynthetic processes (Tripathy et al, 1996) and stress metabolism responses related to hypoxia (Porterfield et al, 1997b).…”

Oxidative Stress and Antioxidant Capacity in Barley Grown under Space Environment

“…1,[3][4][5][6][7][8][9][10][11] However, many of these studies were conducted on plants germinated on the ground and transported into orbit for short periods, subjecting them to transient responses that may not have been due to the space environment. In this study, we planted and harvested barley in space and transported it to the ground in a frozen condition in order to eliminate hypergravity stress in space.…”