The major goals of this project are to determine how gravity and light responses influence each other in plants and to better understand the cellular signaling mechanisms involved in plant tropisms. This proposed project builds on our previous spaceflight experiments on the ISS (TROPI-1, 2006; TROPI-2, 2010) with the EMCS using the model plant Arabidopsis. In this new proposed project, we plan to confirm and extend our discovery during the recent TROPI-2 ISS experiment of a novel red-light-based positive phototropic response in plant shoots.
Thus, the specific objectives of this proposed research are: (1) To confirm and characterize the novel red light-dependent phototropic response in flowering plants. (2) To investigate the relationship between light and gravity by measuring thresholds in fractional gravity. (3) To determine whether the red light effect on blue-light-based phototropism is a direct or indirect effect.
The Seedling Growth series of experiments (1, 2, 3 and possibly 4) is supported collaboratively by NASA and the European Space Agency (ESA). The experiment will be conducted in the European Modular Cultivation System (EMCS) on the International Space Station (ISS). The EMCS is operated by ESA and is located in the Columbus Module of the ISS.
These experiments can be accomplished with telemetric science and therefore fit with the extremely limited down mass capabilities of current spaceflight opportunities. The EMCS is an automated facility and can be operated largely with telemetry. Experimental containers will be launched via Space-X, and during an experimental run, images of seedling growth responses can be downlinked to Earth. Seedlings will be returned to Earth in the GLACIER freezer.
Project 1: Phototropic curvature
Utilizing the European Modular Cultivation System (EMCS) on board the International Space Station (ISS), we investigated the interaction between phototropic and gravitropic responses in three Arabidopsis thaliana genotypes, Landsberg wild type, as well as mutants of phytochrome A and phytochrome B. Onboard centrifuges were used to create a fractional gravity gradient ranging from reduced gravity up to 1 g. A novel positive blue-light phototropic response of roots was observed during conditions of microgravity, and this response was attenuated at 0.1 g. In addition, a red-light pretreatment of plants enhanced the magnitude of positive phototropic curvature of roots in response to blue illumination. Additionally, a positive phototropic response of roots was observed when exposed to red light, and a decrease in response was gradual and correlated with the increase in gravity. The positive red-light phototropic curvature of hypocotyls when exposed to red light was also confirmed. Both red-light and blue-light phototropic responses were also shown to be a product of directional light intensity. To our knowledge, this is the first characterization of a positive blue-light phototropic response in Arabidopsis roots, as well as the description of the relationship between these phototropic responses in fractional or reduced gravity.
Additional results will be available at the conclusion of the study.
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