The regulatory portion of the Adh gene is exquisitely sensitive to exogenous hypoxic stress, and the important cis-acting elements and transcription factors responsible for Adh regulation are known (Ferl and Laughner, 1989; Ferl, 1990; McKendree et al., 1990; Paul and Ferl, 1991, 1997; McKendree and Ferl, 1992; Dolferus et al., 1994; Lu et al., 1996; Hoeren et al., 1998; Dennis et al., 2000). roots during the flight. However, the patterns of expression were not identical to terrestrial control inductions. Moreover, although terrestrial hypoxia induces Adh/GUS expression in the shoot apex, no apex staining was observed in the spaceflight plants. This indicates that either the normal hypoxia response signaling is impaired in spaceflight or that spaceflight inappropriately induces Adh/GUS activity for reasons other than hypoxia. Plants grown in the low-Earth orbital environments experienced during shuttle flight or space-station experiments often display an altered physiology compared with plants in ground-based controls. 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; Driss-Ecole et al., 2000) and energy metabolism (Hampp et al., 1997), and alterations in the Ace 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). A variety of factors in addition to microgravity have been implicated in the differential metabolisms associated with spaceflight. Elevated levels of ethylene or CO2, reduced levels of available oxygen, and fungal pathogens all contribute to metabolic stress in plants, and all are common in closed environments such as those experienced in current orbital vehicles Vitamin D4 (Tripathy et al., 1996; Bishop et al., 1997; Viktorov et al., 1998; Guisinger and Kiss, 1999; Salisbury, 1999). Hypoxia is of particular concern in space-grown plants as many of the features in plants returning from Vitamin D4 space flight environments resemble those of hypoxically stressed plants, even though the plants were ostensibly grown with adequate levels of oxygen. There are several physiological and metabolic indicators of hypoxia in plants; central among them is an increase in the expression of alcohol dehydrogenase (ADH). ADH is a crucial enzyme for plant fermentative metabolism, which functions in the regeneration of the NAD+ needed to sustain glycolysis and maintain basal production of ATP when the cytochrome chain is arrested under oxygen-limiting conditions (Crawford, 1982; Jackson and Vitamin D4 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, 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. To develop a robust biological sensor for detecting hypoxia-related plant responses in spaceflight environments, Arabidopsis plants were engineered with the GUS reporter gene driven by the Arabidopsis Adh promoter (Chung and Ferl, 1999). The regulatory portion of the Adh gene is exquisitely sensitive to exogenous hypoxic stress, and the important cis-acting elements and transcription factors responsible for Adh regulation are known (Ferl and Laughner, 1989; Ferl, 1990; McKendree et al., 1990; Paul and Ferl, 1991, 1997; McKendree and Ferl, 1992; Dolferus et al., 1994; Lu et al., 1996; Hoeren et al., 1998; Dennis et al., 2000). Further, the Adh promoter responds to stresses other than hypoxia with well-characterized responses to cold, salt, Glc, and abcissic acid (Dolferus et al., 1994; de Bruxelles et al., 1996; Ishitani et al., 1998; Conley et al., 1999; Ellis et al., 1999; Koch et al., 2000). In transformed Arabidopsis plants, the chimeric Adh/GUS reporter transgene responds to exogenous stress in transgenic plants with a similar profile as the native Adh gene (Dolferus et al., 1990, 1994; Chung and Ferl, 1999; Ellis et al., 1999). Arabidopsis bearing the Adh/GUS transgene were flown as part of the PGIM-01 (Plant Growth Investigations in Microgravity) experiment, conducted on the STS-93 mission aboard the orbiter gene. Plant Physiol. 1994;105:1075C1087. [PMC free Vitamin D4 article] [PubMed] [Google Scholar]Dolferus R, Van den Bossche D, Jacobs M. Sequence analysis of two null-mutant alleles of the single locus. Mol Gen Genet. 1990;224:297C302. [PubMed] [Google Scholar]Drew MC, He I, Morgan PW. Programmed cell death and.