Oxygen

The analysis of plant growth in space indicated that microgravity exposure induces a metabolic response in the roots of Arabidopsis that was consistent with the hypoxia (Porterfield 2002). In two separate experiments, measurements of root Alcohol Dehydrogenase (Adh) showed that this enzyme had higher activity in microgravity-grown plants, and that the ADH gene was more expressed.

The transgenic Arabidopsis harboring the Adh linked to the [>-Glucuronidase (GUS) reporter gene has been constructed to address whether hypoxia-induced responses occur in space (Paul et al. 2001). The Adh/GUS reporter was expressed only in roots during flight. However, on the ground when Arabidopsis roots were subjected to hypoxia, the reporter gene was always expressed in shoots even if these organs did not experience hypoxia. According to Paul and Ferl (2002), in space the normal hypoxia response signaling from the root to the shoot could be impaired or Adh/GUS activity is induced for unknown reasons. A 1-g centrifuge in space should be necessary to determine whether a gravity vector could restore the apparent disruption of signaling from the root to the shoot.

Fertilization

Embiy ┬ęgenesis

Fertilization

Embiy ┬ęgenesis

Figure 6-22. Development of Arabidopsis thaliana. This plant model presents a rosette of leaves and a reduced stem. In the culture conditions provided, the vegetative phase ends after 13 days and an inflorescence harboring the flowers grows in the following days. Fertilization occurs after 18 days and is followed by embryogenesis, which lasts about 20 days. Seeds are formed in siliques. A seed-to-seed cycle takes about 6 weeks. Adapted from Musgrave et al. (1998).

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