Characterizing Arabidopsis Root Attractions-2 (Petri Plants-2) - 09.05.18

Overview | Description | Applications | Operations | Results | Publications | Imagery

ISS Science for Everyone

Science Objectives for Everyone
Plants cultivated in microgravity look mostly normal, but space-grown plants have a number of distinct features compared to plants grown in comparable habitats on Earth, most notably in the way their roots grow. The Characterizing Arabidopsis Root Attractions-2 (CARA-2) investigation studies the molecular signals that can cause these changes, including the genetic underpinnings of how a plant senses the direction of gravity. Results can improve efforts to grow plants in microgravity on future space missions, enabling crews to use plants for food and oxygen.
Science Results for Everyone
Information Pending

The following content was provided by Anna-Lisa Paul, Ph.D., Robert J. Ferl, Ph.D., and is maintained in a database by the ISS Program Science Office.
Experiment Details

OpNom: Petri Plants-X

Principal Investigator(s)
Anna-Lisa Paul, Ph.D., University of Florida, Gainesville, FL, United States
Robert J. Ferl, Ph.D., University of Florida, Gainesville, FL, United States

Information Pending

Center for the Advancement of Science in Space (CASIS), Melbourne, FL, United States

Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)

Sponsoring Organization
National Laboratory (NL)

Research Benefits
Space Exploration, Earth Benefits, Scientific Discovery

ISS Expedition Duration
April 2017 - October 2018

Expeditions Assigned

Previous Missions
STS-93, STS-131, Increments 19-24, 35/36, 42/43.

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Experiment Description

Research Overview

  • Plants experiencing spaceflight are quite normal in appearance, but can exhibit growth habits distinctly different from plants on Earth. The Characterizing Arabidopsis Root Attractions-2 (CARA-2) investigation explores the molecular biology guiding the altered growth of plants, specifically roots, in spaceflight.
  • CARA-2 specifically addresses the signaling mechanisms that influence root growth in Arabidopsis plants grown without gravity, and when those changes happen during the root's growth period. By using molecular and genetic tools, fundamental questions regarding the signals that affect how a root knows to grow toward gravity and/or in the opposite direction of the shoot may be answered.
  • This investigation advances the fundamental understanding of the molecular biological responses to extraterrestrial environments. This understanding can further define the impacts of spaceflight on biological systems to better enable future space exploration goals.


The spaceflight environment addresses key gravity-related biological issues using a simple, robust operational approach that has been successfully demonstrated with previous Space Shuttle and International Space Station (ISS) flights. Plants experiencing spaceflight mount an adaptive response that can be measured in terms of patterns of gene expression, and morphological changes in growth and development. During previous spaceflight experiments, it was observed that a remarkable number of gene expression changes occurred during spaceflight that are associated with cell wall restructuring and altered root growth. It was also observed that there were differences in the way two distinct ecotypes of Arabidopsis responded to the spaceflight environment, particularly with respect to inherent root-growth patterns. The Caracterizing Arabidopsis Root Attractions-2 (CARA-2) investigation is designed to tie these observations together.
Previous spaceflight results indicate that removing the effects of gravity can reveal novel root responses that are not observed on earth. In the absence of gravity, but in the presence of directional light, Arabidopsis roots are strongly negatively phototrophic, and grow in the opposite direction of shoot growth; however, ecotype Wassilewskija (WS) and Columbia (Col-0) display two distinct, marked differences in their growth patterns. Root growth in WS slant, or “skew”, strongly to the right on the surface of agar plates on orbit, while Col-0 grows with little deviation away from the light source. In the absence of light, the roots of Arabidopsis ecotype Landsberg also demonstrate an inherent skew to the right, while Col-0 appears to grow randomly on orbit. Until now, skewing and waving were thought to be gravity-dependent phenomena, but the APEX-TAGES experiments demonstrated that these characteristic patterns of growth are both independent of gravity and influenced by light.
Among the genes that differ between WS and Col-0, one major gene of interest is phytochrome D (phyD) which encodes a protein involved in light-mediated signaling, especially shade avoidance. The phyD gene in WS contains a deletion which results in the translation of a faulty protein. However, although WS lacks phyD, it does contain normal levels of phyA, phyB, and phyC. There is considerable overlap in the roles of the members of the phytochrome family, and it is difficult to single out the specific role of each. However, a mutation in phyD in a Col-0 background mimics some of the phenotypic features of the WS ecotype. Phytochromes are also of interest, as they have a demonstrated role in phototropism in roots. These effects can be difficult to evaluate in a unit gravity environment, but microgravity experiments have indeed demonstrated that at least two members of the family, phyA and phyB, play a role in positive phototropism in roots.
The hypothesis to be tested is that the differences between the WS and Col-0 can reveal key genes involved in the morphology of root growth on orbit. Further, it is hypothesized that phyD contributes to the light-mediated signal transduction that influences the tropic direction of root growth on orbit, and that Col-0 plant deficient in this gene mimics the negatively phototrophic patterns of WS roots on orbit. The fundamental scientific relevance of this experiment is that it can provide insight into the signal transduction pathways that control tropism and adaptive physiology in plants. The experiment also showcases how the unique research environment of the ISS can provide insight into fundamental and widely applicable biological questions that cannot be answered on Earth, where gravity would mask many of the underlying phenomena.

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Space Applications

Research in space shows that plants experience a wide range of changes in response to microgravity, including differences in the manner in which their roots grow. Without gravity, plants roots typically grow away from a light source. With neither gravity nor light, plant roots must rely on the guiding signals coded in their genes. In some plants, the result is an almost random pattern, while in others, the code directs rots to grow away from where it sprouted ion a distinct patterns, like a consistent skew in one direction. This investigation uses the Light Microscopy Module hardware to capture images of Arabidopsis thaliana plants growing in petri dishes, and also uses fluorescent reporter genes to see into the root cells as they grow, getting a glimpse into how some of those codes are used during spaceflight. In addition, the plants will be preserved in chemicals that allow scientists to study global changes in the plants’ gene activity – looking at how all the codes work together to adapt plants to the spaceflight environment. Results can provide new information on the key genes and proteins involved in how plants detect light, and avoid shade, when extending their root systems. Such genes could be modified to develop plants that grow more effectively in space or in future colonies on the moon, Mars, or other destinations.

Earth Applications
When faced with a new challenge, plants and other organisms activate genes in different ways, which can enable them to adapt to new conditions. Results from this investigation provide a deeper understanding of how plants respond to a novel environment, benefiting efforts to grow crops in drought, in excess carbon dioxide, and in other extreme conditions humans could face on Earth in the future. In addition, this investigation also benefits efforts to understand how plant roots seek nutrients and water, benefiting agricultural research.

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Operational Requirements and Protocols

  • Petri Plates launch in cold stowage hardware at +4°C.
  • Petri Plates are transferred to ISS cold stowage at +2°C until ready for use.
  • Petri Plates are removed from cold stowage and the Duvetyne covers are removed
  • Petri Plates are attached to a Fabric Mount in a brightly lit ISS location.
  • Photographs are taken of each Petri Plate at various time points throughout the experiment.
  • Two Petri Plates are imaged using the Light Microscopy Module.
  • Following a 15-day experiment run, Petri Plates are trashed.
Two sets of three Petri Plates are unwrapped by the crew, and one Petri Plate from each set is installed into the Light Microscopy Module (LMM). The LMM is operated from the ground, with the investigators working closely with the LMM team to obtain ideal images. Once a plate is finished with LMM imaging, it is discarded. The other Petri Plates are photographed at different time points throughout the experiment, and discarded upon completion of the experiment.

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Decadal Survey Recommendations

Information Pending

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Results/More Information

Information Pending

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Related Websites
Dr. Anna-Lisa Paul, University of Florida
Dr. Robert Ferl, University of Florida
Space Plants Lab, University of Florida
Universe Today

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