Biocompatibility studies in preparation for a spaceflight experiment on plant tropisms (TROPI)

The interaction among tropisms is important in determining the growth form of a plant. Thus, we have developed a project to study the interaction between two key tropistic responses (i.e., gravitropism and phototropism) to be performed in microgravity on the International Space Station (ISS). Specifically, we are interested in the role of red-light-absorbing phytochrome pigments in modulating tropisms in seedlings of Arabidopsis thaliana. This project, termed TROPI for tropisms, is to be performed on the European Modular Cultivation System (EMCS), which provides an incubator with atmospheric control, lighting, and high-resolution video. The EMCS has two rotating centrifuge platforms so that our experiments can be performed at microgravity, 1g (control), and fractional g-levels. In order to optimize these spaceflight experiments, we have continued ground-based technical tests as well as basic science experiments. Since the seeds will have to be stored for several months in hardware prior to use on the ISS, we tested the effects of long-term storage of seeds in the TROPI EUE (experimental unique equipment) on germination rates and plant growth. The EUE consists of five seedling cassettes with LED lighting and a water delivery system in an Experimental Container (EC). Preliminary studies showed that there were reduced seed germination and plant growth after several months of storage in the EUE. We determined that the likely source of this biocompatibility problem was the conformal coating of electrical components of the EUE, which was required by NASA for safety reasons. In order to alleviate this problem, carbon filters were added to both the seedling cassettes and to the base of the EC. We expect that these improvements to the hardware will result in healthy plants capable of robust tropistic responses in our spaceflight experiments.