Advanced Plant EXperiments 03-1 (APEX-03-1) - 11.25.14
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Advanced Plant EXperiments 03-1 (APEX-03-1) continues a highly successful investigation into the effects of microgravity on the development of roots and cells on plant seedlings. The experiment uses the model plant Arabidopsis thaliana, or thale cress, which is grown in Petri plates for a specified duration. After the growth period, the plants are photographed, harvested, and preserved for return to Earth and detailed analysis.
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Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Human Exploration and Operations Mission Directorate (HEOMD)
ISS Expedition Duration
September 2014 - March 2015
Previous ISS Missions
APEX-03-1 builds upon the previously flown Biological Research in Canisters (BRIC)-16 experiment which flew on STS-131.
- Despite decades of research, many of the molecular mechanisms by which gravity regulates plant development remain poorly understood. It is likely that in addition to gravitropism, a number of fundamental plant developmental processes that are influenced by gravity have yet to be discovered.
- The goal of the APEX-03-1 research is to utilize the unique microgravity environment provided by the ISS and the model plant Arabidopsis thaliana to uncover novel pathways that orchestrate the complex cellular processes by which gravity shapes plant development.
- The hope is that knowledge gained from this research will also translate into a deeper mechanistic understanding of molecular pathways that govern root growth and cell wall development, which in turn will benefit agricultural practices and bioenergy research on Earth.
The overall goal of APEX-03-1 is to uncover the underlying molecular mechanisms by which microgravity impacts cell wall architecture in the model plant Arabidopsis thaliana, using the VEGGIE facility housed on the ISS. This research builds on a robust dataset from BRIC-16, which flew on STS-131. Through experiments with the BRIC hardware, the science team discovered that spaceflight had a profound influence on the expression of genes involved in regulating cell wall architecture. This led to a hypothesis that plants respond to microgravity through the transcriptional reprogramming of genes that control cell wall remodeling. Because of the prominent root developmental phenotypes (i.e. primary root skewing and inhibition of root hair growth) that were observed in the BRIC-16 experiment, it appears that microgravity-dependent changes in cell wall-related transcripts are predominantly manifested in roots. Furthermore, because primary root and root cell wall ultrastructural defects were most pronounced in a mutant to a vegetative actin isoform (act2), it is hypothesized that microgravity predominantly affects genes that lie within signaling networks linking the actin cytoskeleton with the plant extracellular matrix. Given the successful experiments with BRIC-16, the science team is in an excellent position to effectively utilize the unique capabilities of the VEGGIE Facility on the ISS to test the aforementioned hypotheses.
A new algorithm was developed from the BRIC-16 experiments and is utilized here. The algorithm allows the science team to more rigorously quantify root growth behavior of wild-type, and a higher order vegetative actin mutant (act2 act8 double mutant). This clarifies the extent of actin involvement in specifying root orientation and cell wall remodeling in space. Through the use of monoclonal antibodies and immunocytochemistry, the science team also determines how the distribution and abundance of specific cell wall components change in microgravity, and correlate such changes with root developmental responses and modifications in gene expression.
Finally, more sensitive deep sequencing technologies (e.g. RNA-Seq) is employed to discover novel microgravity-induced transcriptional changes in plants. Knowledge from these spaceflight studies is then translated into corresponding gene functional studies (e.g. mutant analysis and overexpression), which the science team expects may lead to the discovery of new players that modulate root development on earth and in microgravity.
The role of gravity in regulating plant development, especially seedlings, remains poorly understood, and scientists expect that molecular pathways related to gravity remain undiscovered. Experiments on the STS-131 space shuttle mission showed that microgravity has a profound influence on genes that regulate cell wall development. Understanding these pathways will help guide genetic engineering of plants to support long-term space missions and planetary exploration.
Understanding the molecular and genetic mechanisms that control plant development will help provide fundamental tools for improving agricultural and bioenergy research on Earth. It will help in designing crops that use resources more efficiently.
- Time between launch and installation into VEGGIE: 7-12 days
Experiment run duration: 11 days
- Harvest of five plates after 6 days
- Time between harvest and MELFI insertion: ≥ 24 hours
- Harvest photos required; request live video of harvest operations when possible
Only the KFTs return
- KFTs return at +4°C and -20°C in Cold Bag
VEGGIE is prepared for the APEX-03-1 experiment by installing petri plate holders. Six petri plates are removed from Cold Stowage and transferred to VEGGIE. After an experiment duration of 7 days, the first set of petri plates is removed from VEGGIE and transferred to the Maintenance Work Area for the harvest activity. The harvest activity requires the crew member to use forceps to pull the plants from the agar surface on the petri plate. The plants are placed into KFTs and actuated to deliver the Paraformaldehyde Glutaraldehyde, or RNALater chemical preservative to the plants. The KFTs are then transferred to cold stowage. After an experiment duration of 11 days, the second set of petri plates are removed from VEGGIE and transferred to the Maintenance Work Area for the final harvest activity. In total, four Paraformaldehyde Glutaraldehyde KFTs and four RNALater KFTs are used to harvest the APEX-03-1 petri plates. The Paraformaldehyde Glutaraldehyde KFTs are transferred to cold stowage at +4°C, and the RNALater KFTs are transferred to cold stowage at -80°C in MELFI. The KFTs return to earth at +4°C (Paraformaldehyde Glutaraldehyde) and -20°C (RNALater).
Ground Based Results Publications
Hou G, Kramer VL, Wang Y, Chen R, Perbal G, Gilroy S, Blancaflor E. The promotion of gravitropism in Arabidopsis roots upon actin disruption is coupled with the extended alkalinisation of the columella cytoplasm and a persistent lateral auxin gradient. Plant Journal. 2004 Jul; 39(1): 113-125.
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