Analysis of a Novel Sensory Mechanism in Root Phototropism (Tropi) studies Arabidopsis thaliana plants sprouting from seeds to gain insights into sustainable agriculture for future long-duration space missions.Principal Investigator(s)
NASA Ames Research Center, Moffett Field, CA, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)Research Benefits
Information PendingISS Expedition Duration:
October 2009 - September 2011Expeditions Assigned
21/22,23/24,27/28Previous ISS Missions
While Tropi is a new experiment, other studies of plant growth and development have been conducted on ISS.
Analysis of a Novel Sensory Mechanism in Root Phototropism (Tropi) consists of dry Arabidopsis thaliana (thale cress) seeds stored in small seed cassettes. A. thaliana is a rapidly growing, flowering plant in the mustard family. The seed cassettes are contained inside the European Modular Cultivation System (EMCS). The seeds are installed into the EMCS dry and at ambient temperature until hydrated by an automated system of the EMCS. At specified times during the experiment; the plants are stimulated by different light spectrums and by different gravity gradients. The only operations required by the crew are to replace video tapes and harvest the plants following growth. Once the plants are harvested, they are stored in the Minus Eighty Degree Laboratory Freezer for ISS (MELFI) until they are returned to Earth (STS-116 and STS-117). Investigators gather data from video-taped images of the plants, observing their roots as they undergo development in the EMCS, as well as conducting biochemical analyses of the returned plants.
During long-term space exploration, it will be necessary to provide crewmembers with regenerative sources of food, as well as supplemental methods to recycle carbon dioxide into breathable oxygen. As new information about how plants grow in microgravity emerges, sustainable plant-based life support systems may be developed.Earth Applications
Further understanding of how plants grow and develop at a molecular level can lead to significant advancements in agricultural production on Earth.
During its ascent, Tropi requires no resources. The dry seeds are contained in five seed cassettes located in the EMCS. Once in orbit, the seeds are hydrated automatically. Video is taken throughout the experiment, allowing the ground team to evaluate and study the development of the plants. Ninety percent of the science return is based upon video analysis. The crew harvests the plants and stores the specimens in MELFI. They are also required to change out the video tapes.Operational Protocols
Seed cassettes containing dried Arabidopsis thaliana seeds are initiated in the EMCS automatically. The EMCS introduces water to the seeds to activate growth. Video cameras record the growth and development of the plants. Once the plants are grown, the crewmembers harvest the plants and place them in the cold storage in MELFI. The plants are returned to the ground team for further study.
Tropi was a multi-part experiment aimed to gain a better understanding of how microgravity affects phototropism, directed growth of a plant in response to a light stimulus, and gravitropism, directed growth in response to gravity, in Arabidopsis thaliana. An in space experiment was necessary because the microgravity conditions of space provide the opportunity to study phototropism in the absence of gravity (Correll et al 2005).
Tropi was initially performed during Increment 14 on the ISS. These experiments were returned to Earth on three space shuttle missions. Several important lessons were gained from this initial run. The first issue arose while using analog video tapes. Although quality images were taken, there was an inefficient use of resources in the time it took for image processing and analysis procedures to be performed. Another issue arose during the seedling hydration procedure. The initial command did not take place and without video downlinks, the entire experiment would not have been completed. An additional issue arose in seed germination. The seeds were stored from six to eight months prior to hydration and resulted in only 58% germination in the first run with progressive deterioration in the following two runs. The last major issue to arise was found in the transfer of the frozen materials from the shuttle to NASA cooler bags. Because the samples were allowed time to "warm up" during transfer, the RNA from the STS-116 samples degraded. This issue was mediated by implementing a "3 minute rule" in the following runs (Kiss et al 2009).
Although several issues did arise during the first part of Tropi, invaluable information was gained from this experiment. A novel positive phototrophic response to red light was observed in hypocotyls of seedlings that developed in microgravity. It is hypothesized that A. thaliana exhibits red-light phototropism in microgravity, while on Earth it is suppressed by normal gravity. A greater phototrophic response was also observed in blue-light-based trials. A more prominent curvature was detected when shoots were briefly exposed to red light followed by blue light (Millar et al 2010).
Investigators had the opportunity to confirm and extend the results of Tropi in a follow-up experiment during Increment 22 on the ISS. Major modifications between part 1 and part 2 of Tropi took place to ensure optimal experimental conditions. Instead of using analog videos to capture images, part 2 used direct downlinks from the ISS. This allowed for much quicker processing of experiment images and results. Due to modifications in the storage time of the seedlings, the second part of Tropi demonstrated better seed germination (approx. 90% ) and improved seedling growth compared to part 1. The last major modification in part 2 of Tropi involved a switch to use powered GLACIER freezers for the transfer of the frozen samples from the ISS to the Space Shuttle then to Earth. These freezers helped to maintain the low temperatures required to keep RNA intact (Kiss et al 2011).
Previous experiments have dealt with the effects normal gravity and microgravity on plant biology, however Tropi tested the effects fractional gravity has on plant development. More specifically, the effect fractional gravity has on hypocotyl and root development. Tropi part 2 confirmed red-light-based positive phototropism found in hypocotyls under microgravity. When gravity levels began to elevate, a decreased response was noted. Under microgravity conditions, roots displayed a positive phototropic response to red light. This response was only observed under microgravity because when 0.1g was induced, the red-light response was attenuated. Tropi was also utilized to determine the relationship between red-light pretreatments prior to blue-light exposure in hypocotyls and roots. Hypocotyls displayed a decreased response in phototropism while roots exhibited an increase response in phototropism when exposed to a red-light pretreatment. In response to these findings, investigators wanted to determine if there was a direct or indirect relationship between the red-light pretreatments in the hypocotyls and roots. In regards to the hypocotyls, these space studies support the concept that red-light is indirectly involved in blue-light-based phototropism through the attenuation of gravitropism. These results support the hypothesis that red-light enhancement of blue-light root phototropism is direct. Taking Tropi as a whole, these observations show that the microgravity conditions found in laboratories aboard the ISS can provide a unique research tool to gain insights into fundamental mechanisms in plant biology (Kiss et al 2012).
Kiss JZ, Millar KD, Edelmann RE. Phototropism of Arabidopsis thaliana in microgravity and fractional gravity on the International Space Station. Planta. 2012; 236(2): 635-645. DOI: 10.1007/s00425-012-1633-y. PMID: 22481136.
Millar KD, Kumar P, Correll MJ, Mullen JL, Hangarter RP, Edelmann RE, Kiss JZ. A novel phototropic response to red light is revealed in microgravity. New Phytologist. 2010; 186(3): 648-656. DOI: 10.1111/j.1469-8137.2010.03211.x.
Kiss JZ, Kumar P, Millar KD, Edelmann RE, Correll MJ. Operations of a spaceflight experiment to investigate plant tropisms. Advances in Space Research. 2009; 44(8): 879-886. DOI: 10.1016/l.asr.2009.06.007.
Kiss JZ, Millar KD, Kumar P, Edelmann RE, Correll MJ. Improvements in the re-flight of spaceflight experiments on plant tropisms. Advances in Space Research. 2011; 47(3): 545-552. DOI: 10.1016/j.asr.2010.09.024.
Correll MJ, Edelmann RE, Hangarter RP, Mullen JL, Kiss JZ. Ground-based studies of tropisms in hardware developed for the European Modular Cultivation System (EMCS). Advances in Space Research. 2005; 36: 1203-1210. DOI: 10.1016/j.asr.2004.11.003.
Wyatt SE, Kiss JZ. Plant Tropisms: From Darwin to the International Space Station. American Journal of Botany. 2013; 100(1): 1-3. DOI: 10.3732/ajb.1200591. PMID: 23281390.
Matia I, Gonzalez-Camacho F, Herranz R, Kiss JZ, van Loon JJ, Marco R, Medina F, Gasset G. Plant Cell Proliferation and Growth Are Altered by Microgravity Conditions in Spaceflight. Journal of Plant Physiology. 2010; 167(3): 184-193. DOI: 10.1016/j.jplph.2009.08.012. PMID: 19864040.
Molas ML, Kiss JZ, Correll MJ. Gene profiling of the red light signalling pathways in roots. Journal of Experimental Botany. 2006; 57(12): 3217-3229.
Mullen JL, Wolverton C, Hangarter RP. Apical control, gravitropic signaling, and the growth of lateral roots in Arabidopsis. Advances in Space Research. 2005; 36: 1211-1217.
Correll MJ, Kiss JZ. The roles of phytochromes in elongation and gravitropism of roots. Plant and Cell Physiology. 2005; 46: 317-323.
Kumar P, Montgomery CE, Kiss JZ. The role of pytochrome C in gravitropism and phototropism in Arabidopsis thaliana.. Functional Plant Biology. 2008; 35: 298-305.
Kiss JZ, Kumar P, Bowman RN, Steele MK, Eodice MT, Correll MJ, Edelmann RE. Biocompatibility studies in preparation for a spaceflight experiment on plant tropisms (TROPI). Advances in Space Research. 2007; 39(7): 1154-1160. DOI: 10.1016/k.asr.2006.12.017.